Switching Matrix Test Bed

Many of the antennas I've described on this blog include a simple or an elaborate switching systems. These are useful for direction switching in low band multi-element antennas, selection of receive antennas and for stacked yagis (e.g. up, bottom, both). The more elaborate switching systems consist of many relays whose operation must be orchestrated so that every array element is correctly configured and the antenna behaviour can be switched with low-voltage cable from the operating position that may be 100 meters or more distance from the antenna.

Switching matrices for antennas are straight-forward and use common components in a repetitive pattern. Even so it is worthwhile to pay attention to details. With the low-band directional receive and transmit antennas I aspire to build in my next station this is a topic that will become a priority. Some experimentation with these devices is time well spent.

The transmission line cannot be easily used for this purpose since there may be many configuration states and there is only one DC path (assumes a bias-T to allow coax to carry both RF and DC). Instead we use a multi-conductor cable with one common wire and other wires assigned to each configuration state. For example, in the 3-element vertical yagi for 80 meters I earlier described the cable would require 7 wires: 1 common; 4 for each antenna direction (unpowered it is in omni-directional mode); 1 to select CW or SSB band segments; and 1 to select 160 meters.

Since a picture is reputed to be worth 1,000 words I'll reproduce the schematic of a switching matrix taken from ON4UN's Low-band DXing book. I chose this one for its clarity and no other reason. Also, I was reminded of the book when I had a short QSO with John on 20 CW while writing this article.

In this matrix the common line is negative; it can be the positive line if you prefer and you do not share a common return path with the coax outer conductor. One of the horizontal wires is energized by the operator activating a switch. Each relay coil has a vertical conductor to complete the matrix. A switching diode is placed at the junction of each horizontal and vertical line where for that operator selection the relay is to be energized. Depending on the application the relays and what they switch can be quite different, however the circuit topology remains the same.

I think any ham looking at this schematic would quickly understand it despite its size. The topology is straight-forward and the circuit elements are basic. Perhaps there's nothing to learn here, just a standardized approach for those planning switching arrays for receiving antennas or even wire yagis. There are other topologies possible, such as those requiring fewer wires but requiring binary coders and decoders. Since a long run of small gauge wire is inexpensive it is rarely worth the added complexity.

Despite the simplicity of the approach there are benefits to having a test bed for evaluating components and circuitry before diving into building switching matrices and their attendant interfaces and supporting hardware (and software). To this end I dropped by a local electronic parts retailer and filled a bag with some odds and ends to build a combination test bed/prototyping tool. It was very inexpensive. Here it is:

As you can see it doesn't need to be pretty! The components of the test bed include a punch-down prototyping board and a bundle of switching diodes. This board is large enough to prototype a switching system with 5 or 6 relays rated for 10 A. The 3 A PCB-mount relay looks tiny compared to the board. It was purchased only for the purpose of testing the test bed.

Wires, power supply and multi-meter were already in my workshop. I grabbed wires from my junk box that were already suitable for the task rather than make new ones. That contributes to making it look messy. Colour-coded wires cut to size are recommended when building a prototype.

The multi-meter in the photo is measuring DC voltage across the relay coil. At other times it was in resistance mode to monitor contact open and closure.

Now that the test bed is built let's review the ways in which it can be used.

Component testing

There was a time when semiconductors, relays and other components that were available retail had a DOA rate of several percent. Even though this has improved there is some comfort to be had by testing relays and diodes before soldering them to the PCB. Some use sockets for relays, but that can be expensive and introduces another source of future trouble: contact corrosion.

Not all relays have their terminals labelled. The one I purchased doesn't. The test bed can be used to identify the terminals. You can see that I drew a diagram to record what I found. Make sure that all the relay contacts -- NO for normally open and NC for normally closed -- show the expected zero or infinite resistance in each state.

It can even be useful to test diodes since the cathode marking may be unclear unless you are familiar with the component and its package style. I mounted two diodes in opposite directions to confirm the markings are as expected.

Circuit topology

The prototyping board has a similar layout to off-the-shelf pre-drilled PCBs. There are just fewer bus lines, thus requiring more jumpers. After the full prototype is built take a picture of it and transfer the components to the PCB, retaining the same positions. Solder and test in stages and you're done.

Keep in mind that the orientation of the diodes (direction the cathode faces) depends on whether the circuit uses the negative or positive DC bus as the common point for all the relay coils.

Component ratings

Relays and diodes are simple components yet they do have ratings you should be aware of. These can be tested.

First, you should check two voltages of relay operation: turn-on and turn-off. The first is the minimum voltage to positive relay closure. The other is the voltage below which an energized relay full opens. These can be read from the spec sheet if it is available (typical values are 70% and 20%, respectively). But that may be impossible for old stock or parts pulled out of a junk box. The more forgiving the relay operating voltages the more flexibility you have in choosing long runs of small gauge wire. By turning off the power supply and watching the voltage drop I estimated at most 3 volts when the relay opened (< 25%). I didn't measure the turn on voltage.

Second, you need to account for the diodes. Notice in the picture the voltage reading is 13.05 VDC even though the power supply is 13.8 VDC. A silicon junction has a forward voltage drop of 0.7 volts (±0.2 depending on current and temperature). The multi-meter probe is connected to the relay side of the switching diode so that the voltage drop can be seen.

When multiple relays are energized by one diode the diode current and power ratings can become important. The 1N4148 diodes I am using have a current rating of 200 to 300 mA. The coil of the test relay has a DC resistance of  700 Ω (measured as 680 Ω). For a supply voltage of 12 VDC (e.g. 13.8 minus wire loss), leaving 11.3 VDC across the coil, the current through the circuit is 18 mA, with the diode dissipating 13 mW due to its 0.7 volt drop.

This isn't much. However this is a small relay. For a typical 10 A rated SPDT relay for this RF application (e.g. Omron G2RL: 12 VDC, coil resistance 360 Ω) switching systems the current is 31 mA and the diode dissipates 22 mW. Multiply these amounts by the number of relays simultaneously energized by one diode in the matrix.

Go beyond a diode load of 6 relays and you might run into trouble, or even with fewer relays on a hot day when the temperature soars inside the enclosure. A higher capacity switching diode may be desirable in those cases. The 3-element vertical yagi for 80 meters comes close because the switching matrix powers up to 2 relays (float and reflector/director) at each of the 4 parasitic elements.

Summertime notes

I now enter the summer season. Expect the pace of articles on the blog to slow during the next 2 or 3 months. It's not just summer but also that some changes are afoot, about which I expect to say more later as my plans firm up.

I also have a trip back home to VE4 coming up very soon. I may come back with a few pictures related to amateur radio, something I neglected to do on my previous trip west.

For those operating in ARRL Field Day this weekend, have fun out there. From past experiences I've decided to avoid operating out of doors since it doesn't agree with me. I have many stories of past FD misadventures that only seemed funny to recount well after the fact. I enjoy outdoor adventures and amateur radio, just not at the same time!

Informal Station Comparison on 6 Meters

With sporadic-E (Es) season underway I decided to be active even though, unlike last year, I chose to not bother with a 6 meter antenna. In fact I've made no changes to my station this year, which is a subject for another time. For the present I am selecting the antenna that seems to work best on 6 meters, on the basis of receiving signal level, which is my Hy-gain Explorer 14 tri-band yagi up 15 meters.

The antenna works surprisingly well once the mismatch has been tamed by the transceiver's internal tuner. In the past several days I added 7 DXCC countries (now 18 on this band) and made close to 100 QSOs in the ARRL June VHF contest while operating part time.

But how to tell how well it works? Perhaps the best way is to compare performance with another station while quantifying as far as possible the differences. The opportunity arose when I recently added 6 meters to a friend's K4KIO Hex Beam, a kit he omitted when the antenna was bought a few years ago.

I only had the idea when I found that we were calling the same DX stations. Although we are some distance apart we can hear each other on ground wave. We are enjoying the friendly competition. Since we are both experienced DXers our techniques are comparable. This matters since a timid, overly aggressive or inexperienced operator will often lose out when the opening is marginal and the competition fierce.

I'll step through the elements of the station comparison then discuss how we fared against each other.

Height and terrain

While I was on his tower I noted that his antenna is at the very same height as mine -- 15 meters -- with a similar flat topography in the direction of Europe. There are more houses around me while he has more trees in his semi-rural location. A more exact comparison would be extremely difficult. Let's call this one a draw.

Antenna gain

The hex beam is a two-element yagi on all bands from 20 through 6 meters, with separate wire elements for each band. The elements, and especially the driven element, have numerous bends. The bends reduce gain a small amount below the 7 dbi that theoretically possible for a 2-element yagi. I would estimate the gain on 6 meters to be 6 dbi. The Moxon-style coupling between elements affects F/B and match but not gain.

Much to my surprise the Explorer 14 has a F/B on 6 meters. I expected it to behave more like a long dipole. While it does exhibit the additional lobes (6 total) of a long dipole there is about a 2 S-unit different in ground wave received signal strength between the forward and backward (broadside) directions. I measured this with the VE3WCC beacon on 50.009 MHz in FN15. I receive the beacon at S5 strength when pointing its direction.

With no way to measure the actual gain I can only go on what I can measure and theory. For theory I followed the principle of subtractive arrays that when signal is removed in one direction it appears as gain in another direction. However it takes a lot of F/B to add noticable gain with the yagi elements loosely coupled on 6 meters due to element separation. My guess is 3 dbi gain, or about 1 db better than a simple dipole.

Transmission line loss

My transmission line length is about half his: 30 meters vs. ~60 meters. Mine is a single length of RG-213 in very good condition; his is approximately half "well-aged" RG-213 and almost new LMR400. Loss can be accurately measured though not easily or conveniently enough for this casual comparison. Instead I plugged some numbers into TLW to estimate the transmission line loss.

I assumed that the RG-213 in my station has a loss comparable to new cable. In his I mentally balanced the higher loss of his weathered RG-213 and the better quality LMR400 and judged it to be comparable to a single run of new RG-213. The input side SWR at his station is 1.5 and 2.7 at mine.

TLW does the rest once I find a combination of resistance and reactance to give the measured SWR. It is sufficient to set the reactance to zero and only adjust the resistance in this exercise since both components rotate around the Smith chart many times along the coax which is long compared to wavelength. I could have measured these values at my station easily enough but there was no point.

Tuner loss

I use a tuner; he doesn't. Compact tuners for such a wide frequency range -- 1.8 to 54 MHz -- can be quite lossy at the extremes of the range. Loss further increases with the ratio of the impedance mismatch. I'll be optimistic and guess -1 db of tuner loss for the input side SWR of 2.7, which equates to 4.8 at the load due to transmission line loss.

It is possible to achieve greater accuracy by comparing power output to my Bird dummy load. I have done so in a casual fashion, enough to tell that the loss is probably not as great as I estimated. I am being conservative in my estimate to compensate for my avoidance of rigourous testing.

Adding it all up

With all the numbers in hand I proceeded to plug them into a spreadsheet and do the sums.

The difference is ~3 db. Although not large it is significant. Who wouldn't want 3 db of performance, on any band? Now we come to the on-the-air comparison. Does his 3 db beat me out?

To my surprise the answer is a firm "no". A few DX stations would respond with "VE3?" when we called simultaneously, yet it is a toss-up for who got through first. Repeated several times with different DX stations, and the vagaries of different fading patterns at our separated locations, we seem to do equally well. Perhaps equally poorly is more correct.

In a couple of cases neither of us made the QSO, never getting beyond copy of our commonprefix at the other end. Alternating our calls rather than calling atop one another made no appreciable difference.

Conclusion

One has to question whether the comparison is valid or whether 3 db is less of an improvement than we might wish to believe. To that I have no good answer. What it ought to make you wonder is how far you will or should go and how much you will spend to gain a decibel or three. Some will go quite far. Others refuse to go there at all.

There is no magic balance point that represents an optimum of performance or finances. It's a personal choice. Then there are the exogenous factors of terrain and propagation that are quite a lot more difficult to deal with.

A comparison like the one described serves only to demonstrate how elusive performance gains can be in practice.

Adjust a Yagi by Pointing It Up

The bigger the antenna the more difficult it is to tune. When done near the ground you are at risk of seeing its performance be worse when raised to full height due to the change in ground interaction. When done in the air the tuning process is difficult and potentially dangerous. Modelling can help to compensate for the height differential, but it is no panacea since software ground is rarely similar enough to real ground. Also, there are other environmental influences at low heights.

For yagis one technique many hams have had success with is to point the yagi straight up from a low base height. The idea is to get the antenna (reflector element) just high enough off the ground that its performance is comparable to that in free space (and therefore also at its intended height), and laterally offset far enough from the tower to avoid mutual coupling that will skew its behaviour. But close enough that the feed point is within easy reach. I've used this technique several times. It can work very well indeed.

Hy-gain 155BA prepared for tuning at
VE3CRG's station circa 1985

An example of the technique is shown in the adjacent photo, which I scanned from an old 35 mm print. The yagi isn't quite in tuning position for this photo op, with one side of the antenna too close to the tower. The rope attached to the reflector was used to stabilize and orient the yagi for tuning.

A casual internet search however shows an awful lot of unsubstantiated opinion and misinformation mixed with the good advice. When you do it right the technique works, so that's what we'll explore in this article.

Yagis are not dipoles -- even though they are comprised of dipole elements. Yagi behaviour does not go through the wild swings as height is varied, unlike what we see with single element antennas. Yagis are more immune to ground effects, becoming stable at surprisingly low heights (in terms of wavelength). Why that is true is interesting and worth exploration.

What the technique can and cannot do

The only performance parameter that can be conveniently adjust by this technique is the match; that is, optimizing the SWR across the band or band segment of interest. Gain and F/B optimization require other techniques, such as accurate modelling, including stepped diameter correction (SDC), field strength test range or testing with a cooperative ham within ground wave range.

Apart from that, like most hams we will have to trust the manufacturers' published dimensions for each band segment and for gain and F/B performance. If you don't trust the manufacturer (this can be an issue) design your own yagi.

With today's accurate software models and antenna analyzers it is still difficult to test and tune large yagis at the tops of towers, even if only for purposing of achieving a good 50 Ω match. For yagis with other than 3 elements the feed point is often not even within reach from the top of the tower.

Statement of objectives

We want the best possible match to minimize transmission line loss and maximize flexibility in the shack by having antennas that work well with transmitters and amplifiers that require a low SWR. The vertical pointing method is useful for conveniently adjusting the SWR of large yagis.

Or is it? Does it work, and how well does it work? Computer modelling helps us to answer these questions. The less we have to adjust our antennas at height the less chance for an accident. The best tower safety practice is the one that doesn't require a trip up the tower at all.

Test antenna model: 3-element 20 meter yagi

Rather than explain what's going on and then verify with models or measurements I will start with the model to see what it can tell us. For this exercise I will use a 3-element 20 meter yagi on a 0.35λ boom, a model I've used before as a reference for designing and evaluating tri-band yagis. This antenna is similar in scale to a Hy-gain TH6DXX but without the performance impact due to trap loss and element shortening. The model includes a hairpin (beta) match to achieve a 50 Ω match.

The following chart is from the referenced article, reproduced here for convenience. In particular notice the variation in F/B with frequency: its importance will become clear later in this article.

First we need to model the reference antenna in free space as our basis of comparison. Next, the antenna is rotated upward and placed over real ground (EZNEC medium ground). Its height is then varied and its SWR and gain calculated and compared to the reference. For what ought to be obvious reasons the F/B cannot be compared (see the adjacent elevation pattern).

Sample elevation pattern of a vertically pointing yagi;
the pattern can be quite odd in this configuration

When the impedance across the band is comparable to the antenna in free space we can usually trust that the gain and F/B are also in accord with the free space model. So if we can achieve this with the yagi in its vertical test position it should do fine when raised to the top of the tower.

Proper test setup

The yagi must be carefully positioned on the tower for this tuning method to be reliable. First, by height I mean the height of the centre of the reflector (bottom) element. I am ignoring element droop since its effect is only noticable at very low heights and for light duty elements with significant droop. Coupling is greater for the element tips and these will be closer to ground than the rest of the element.

Yagi model pointing up

The model does not include the antenna boom, tower and guys. The boom and element clamps do affect element tuning but are not relevant to our model experiment since we are looking for a change in behaviour not the absolute performance data. I further assume that guy wires are non-conductive or well broken up so as to have near zero mutual impedance with the antenna, and that the tower is "invisible" when the boom is outboard at least 1 meter from the tower and the elements are orthogonal to a line between tower centre and antenna boom.

This can be accomplished with a length of pipe or angle iron projecting outward from the tower with a pulley at its extremity and secured with ropes so that the antenna doesn't rotate in the wind, as shown in the photograph earlier in this article. It does make a difference, as I have discovered in practice when a breeze comes up and the SWR starts climbing.

If the boom is especially long it can be difficult to avoid guy wires when lifting the yagi into position for tuning. If necessary remove those elements, lift the antenna and reattach the elements.

As with all antennas a common mode choke should be used to prevent feed line radiation from disturbing the performance. The coax should be dropped straight down, either off the bottom end of the boom or along the tower vertex nearest to the boom.

Performing the comparison

I start with the antenna at a height of 2 meters (centre of reflector element to ground). The antenna is then raised in increments and its SWR and gain recalculated. The SWR and gain are calculated every 50 kHz from 14.000 to 14.350 MHz. This is sufficient granularity to derive an insight into what is going on, as we'll see; we don't need to know the R and X values of the feed point impedance, although that can be interesting and important in other instances.

At just 1 meter height (0.05λ) the SWR is already barely distinguishable from the antenna's SWR in free space. Going higher changes little. Are you surprised? Let's do it again, this time with the antenna in its normal horizontal orientation, stepping through the same heights.

Now we see that low heights have a large impact. Only when at a height of 5 meters (0.25λ) does the SWR become close to that in free space. At 10 meters height (0.5λ) the SWR is nearly indistinguishable from what it is in free space.

This confirms the technique where many hams with big towers mount their large yagis for tuning on a short tower before placing them at their final height. But now we also know that the "yagi tuning tower" should be no less than 0.5λ, at least for this antenna. Keep this in mind should you find it easier at your station to tune yagis horizontally rather than in the vertical orientation we are focussing on.

Let's move on to the gain comparison with the antenna rotated back to its vertical orientation. The results may be less surprising now that you've seen how the SWR responded. Yet the behaviour of the gain is somewhat unusual.

The yagi's gain has a complex relationship with height; there is a cyclic component due to minor lobe ground interactions. Influences include: mutual impedance with ground; ground reflections; and, directions and magnitudes of rearward nulls and minor lobes. While not shown the patterns develops odd lobes with small changes in height. The gain variation is within about 1 db, which is quite modest. If it were bigger we'd have likely seen greater fanning out of the SWR curves.

What is clear is that frequency has a stronger influence on the gain differential. SWR variation shows a similar though less pronounced trend (weak but visible correlation). This is where we need to step back and review how yagis work. Therein lies the explanation.

Why it works: mutual impedance

A yagi is a subtractive array. Strong mutual coupling among close-spaced elements causes field cancellation in some directions and field reinforcement in other directions. The relationships can be quite complex, which is why yagi optimization was so difficult in the years before software tools such as NEC were available.

Field cancellation reduces the radiation resistance which in turn increases element currents. When those currents are approximately in phase there is gain in that direction, accentuated by the higher current. Recall that the current (and antenna aperture) determine field strength. In contrast, additive arrays -- ones where the elements are far enough apart to have low mutual impedance -- work on superposition alone since the near field effects are relatively small.

Yagi elements also interact with the ground. Ground is in essence a flat, non-resonant medium that is lossy. That loss and ground's dielectric properties in combination with the induced current cause the phase and magnitude of the re-radiated field to vary with angle and polarization. It's messy but (mostly) able to be modelled. NEC4 perhaps does it best. EZNEC does pretty well with NEC2 and its real ground ground models.

Off the back end of a yagi that coupling is reduced since the cancellation of fields leaves less to interact with the ground. As long as the magnitude of minor lobes in the back 180° is small relative to the forward lobe the effects can be quite small. We can say that the strong mutual coupling between the yagi elements dominates the mutual coupling between the yagi and ground.

The gain differential with height for the yagi pointing upward correlates with the F/B. That's why I suggested keeping the plot of F/B in mind for this discussion. Notice that the free space F/B is highest at 14 MHz and falls off as the frequency increases. There is enough rearward field at the top of the band to more strongly interact with ground and thus influence the gain. Happily the effect is modest so SWR tuning is little effected when the reflector is quite close to the ground.

Yagis with poor F/B fare less well. This is especially true of 2-element yagis which have poor F/B (except for the Moxon with its critical coupling). These antennas should be raised higher, whether oriented vertically or horizontally, for the tuning to be reliable. Optimized yagis with 4 or more elements typically have excellent F/B across the band and respond especially well to the vertical tuning technique.

Myth and lore

When I first heard about vertical tuning of HF yagis many many years ago I had no understanding of why it worked. All I knew was that reputable names with super-stations used the technique and recommended it. I tried it and it worked. So I kept using it.

A lot of ham radio is like that: we do things that we have heard about but do not understand. Unfortunately this is also a good way to propagate nonsense, of which there is a lot out there.

By gaining a deeper understanding we learn to separate the wheat from the chaff, rejecting the "myth and lore" and adopting that which is science and evidence based. My hope is that this article contributes to the latter even though it only touches on the subject with a few examples. You can run your own models for the antennas you have or are designing to confirm how best to tune them.

7¼ Radials

Last week a few labourers were working in my yard with shovels. With barely visible radials of my 80 meter tower vertical lurking in the grass and weeds the inevitable happened. I was lucky that only one radial was severed. I watched from some distance away while talking with the supervisor and several others with no opportunity to politely intervene.

I knew it had happened when the young man with the shovel looked down with a puzzled look on his face. Perhaps I should have rolled up the radials after all. No matter, the deed was done and I was left to deal with the consequences.

But were there consequences? In fact I was not particularly bothered by the radial damage even though CQ WPX CW was days away. Neither was I concerned about replacement cost since wire is cheap and the radials are only 8 meters long. I went ahead and used the antenna to make a dozen 80 meter contacts in the contest without a qualm. If its performance changed I couldn't tell.

It is worth taking a few moments to delve a little into what is going on here, and to thus explain my lack of concern. Radials are often misunderstood by many hams. Let's start with the most easily measured data: impedance and SWR.

The model view of the disfigured antenna is at right. Wire 24 was chosen to represent the radial damage since it is parallel to an axis, making it easy to change its length, and orthogonal to the 40 meter inverted vee, just like the damaged radial. Modelled SWR curves show the effects.

 

Resonance drifted upward by about 25 kHz (~0.5%). I see greater variation than this when it is raining or snowing, and the ground is thawed or frozen. That is, the change is negligible. The increased ground loss is similarly small, being well under -0.1 db in the model.

With my antenna analyzer I swept the SWR from 3.5 to 3.8 MHz and confirmed that there is no discernible change. I have no means to measure ground loss, other than noting that performance seemed no worse than before; the antenna performance remains poor though servicable.

Returning to the model I calculated the radial currents. As expected the current in the short radial is so small as to be equivalent to the radial being absent. I could just as well have titled this article 7 Radials. Current in the two adjacent radials was reduced less than 10%. Current in the other 5 radials was equal and of the expected magnitude; that is, they are unaffected by the cut radial.

What can we take away from the radial-cutting incident and my analysis? The points to be made are modest but I believe important in better understanding radial behaviour.

• With 8 short radials adding or subtracting 1 radial has a small but measurable effect on antenna resonance. That is, the radials are still acting in part as resonant counterpoises. The effect diminishes with increasing radial counts. With a large number of radials the radial system is more ground plane than counterpoise.
• The loss of one radial increases ground loss only a small amount. Again, the effect declines with increasing radial count. One aspect I did not attempt to isolate was the degree to which the increased ground loss, which is in series with the radiation resistance, affected the frequency of minimum SWR versus frequency of X = 0 Ω. The two frequencies are typically not the same.
• With 8 radials the loss of symmetry -- equal length and spacing -- due to one deleted radial is small, even with the short 0.1λ radials I am using. A similar loss with 4 radials is more dire.

Adding or subtracting one radial is no big deal for other than the most minimalist radial system, whether on the ground or above ground. It is not surprising that studies of radials and actual antenna construction typically discuss performance changes when the radial count is doubled or halved. Large changes in radial count are what make a measurable difference.

For example, if you want to improve the efficiency of your vertical double the radial count. Don't settle for lesser increments. Doing it this way also happens to be the most convenient since you are laying one radial centred between every two existing ones. Nothing needs to be moved. But you'll want to stock up on low-cost wire since doubling radials requires a lot of wire.

[Note: All the links in this article are to other articles in this blog. The referenced articles contain links to outside sources that you may find of interest.]

Tower and Antenna Work: Getting Orgainized

Antenna and tower season has finally arrived in this northern climate. Spring has been unseasonably cool so it is nice to be able to go outside and actually need sun protection. But before we all put a wrench between our teeth and scamper up the tower it is worthwhile to think about it first so that we do it safely and effectively.

Even when we take the utmost care in ensuring the safety of ourselves and others around us the probability of something bad occurring increases if we keep having to climb up and down the tower several times because we forgot to carry the right tools and hardware, or a rope unexpectedly snags.

Some of my recent inspiration for this topic comes from minor surgery I underwent last fall. The experience taught lessons that can be applied to tower and antenna work. I'll take you through some lessons I took away from the surgical experience and relate them to tower and antenna work. The lessons becomes more acute as the size of towers and antennas increase. There is a great deal to be learned from watching any professional going about his or her job, whether they be doctors or carpenters.

Have a plan

As amateur radio operators we too often have a propensity to improvise every task whether it be tower work or building electronic equipment. It seems that drawing up a plan can make a project feel more like work rather than fun. Yet tower work is dangerous business that is deserving of a business-like attitude. This does not preclude having fun and spending time with friends.

Simple things can make a big difference. For example, picking the wrong side of the tower to haul up a rotator or an antenna. Which way is the wind blowing? Get it wrong and expensive antenna elements can be easily bent or broken when snagged in the tower or guy wires, or labour-intensive wire harnesses can be torn apart. All because of a breeze.

An antenna as uncomplicated as a small tri-bander can be surprisingly difficult to orient, stabilize and secure when you're 20 meters up a tower. VHF/UHF antennas are so light and fragile there are even more opportunities for damage. Larger antennas have a lot of momentum when they move and you have little leverage. A common error is to lift the yagi so that the boom-to-mast clamp is on the wrong side of the boom. It can be difficult or impossible to lift the yagi over the mast to correct the error.

Rotating a poorly oriented yagi can be difficult or dangerous because of guy wires or other antennas. You can end up with trap drain holes pointing up rather than down! If you force the matter prepare for trouble. Don't be afraid to drop it back to the ground and try again. Better to think it through the first time and save time and grief.

I know that it's no fun thinking through all this detail before you get to work. On the other hand you can amaze and delight your friends when, after all your fussing, the antenna is bolted in place only minutes after lifting is begun. They may even feel they're the heros. That's perfectly fine. The brighter ones will learn and start planning their own projects as well.

The total project goes faster and safely -- more time spent planning, less time spent doing, and redoing, and redoing again -- leaving more time for the important stuff: enjoying pizza and beer with your friends.

Routine

Surgery nowadays is slickly choreographed, from the time you walk in until you are discharged a few hours later. The majority of the processes followed are the same for everyone; it is typically only the surgical procedure itself that is tailored to the patient. Making a routine of tower work helps ensure that all goes smoothly and no key steps are missed.

Here is part of my routine:

• Keep all common tools, parts and safety equipment in the same place so you know where to find them. Return them there when you're done. Toolboxes, and even boxes, make this convenient. Do this for both mechanical and electrical tools and parts.
• Inspect the tower and environment. Is everything where it should be? Shake the tower and pull on guys and antenna support ropes. Immediately deal with anything out of the ordinary. I am especially strict about this when working on others' towers.
• If you're working alone are you being watched by someone? You want help to come quickly if something goes wrong. It can be as simple as asking your neighbour to glance out the window from time to time.
• Power down the shack. It is too easy for a child or pet to touch a paddle and send 100 watts (or more) to the antenna you're handling. Worse is when the tower is the antenna.

It all seems like common sense, yet many hams make it up as they go along, every single time; they will not learn. Even a modest amount of organization can mean no more tearing the house, garage and shack apart to find everything you need and redoing every task due to unforeseen difficulties. All for what ought to be a 10 minute job!

Tools

With the boxes of tools and parts in front of you walk through the plan, step by step. For each step that requires a tool or part take it and place it to one side. If you have a complete plan and you know the size of every fastener you are almost done. But there will be problems. For example, you may want to use a socket and ratchet driver for a particular bolt, then find you need a deep socket and you picked an ordinary one. You can probably think of more examples.

I do not inventory every fastener used in my towers and antennas. Therefore I expect to be surprised. To cover all the bases  there is a core set of tools I always carry in my tool belt.

The adjustable wrench should only be used when the proper wrench or socket was overlooked. But you'll appreciate it when you're 30 meters in the air and it's all you've got for that one critical and unexpected fastener.

That second wrench may be unfamiliar. The line wrench is designed for nuts that secure lines (e.g. fuel lines) to machinery. The opening fits around the line and grips the nut almost as well as a box end wrench. It is ideal for long bolt shafts on many clamps that won't take a long socket. It won't easily slip off the nut or bolt head when you need let go to reposition your hands or feet. This one has sizes 1/2" and 9/16" which are common on boom, element, mast and rotator clamps.

Removing and installing weatherproofing of connections is so common that a knife and tape are always handy. A screwdriver blade on the multi-use knife can be used in a pinch for working on hose clamps and screws securing electrical connections. Alternatively carry a socket screwdriver with multiple tips.

Don't skimp on your tools! Buy the best you can afford. I have shattered sockets, bent screwdriver blades and otherwise destroyed many tools and hardware that had no business being in my tool belt. Some were handed to me by other crew and some (I'm ashamed to say) were my own choice. Don't make this mistake. It can cost you more than just time.

Finally, carry spare tools and parts for use in case you drop one (or two or three...). It happens. Which brings us to the next topic.

Safety

Don't bet your life, or
antenna, on this rope!

You can go a long way toward having a safe project by following a few simple steps. You want to keep yourself and others safe above all else. But we are amateurs, not professionals, and we do this for fun rather than profit. If you haven't already discovered this the pursuit of fun in tower and antenna work frequently conflicts with a willingness to pursue safety procedures. When it's your station you have the responsibility to make the call of how much safety you will insist upon.

With that said here are a few items to consider. It is by no means complete.

• Check all ropes and climbing harnesses for wear, fraying and other suspect damage. Should you be tempted to use a worn item one last time, don't! If you have to ask the question you know the answer.
• Clear the work area of pets and children. Even when warned away they have a way of sneaking back, drawn by curiosity. There are endless possibilities for injury and mischief. Stop work immediately when they get close.
• Everyone with work or other hazards overhead should as a minimum wear a hardhat. They are inexpensive and modern ones grip the head so that they stay in place when you (frequently) look upward. Keep a few around and hand them out.
• Wear appropriate clothing, even in the summer heat. Showers are cheap, replacing skin and knitting bones aren't. I admit to occasionally breaking this rule to stay comfortable, and accept the risk.
• Are tools and parts stored about your person and ropes run so that they can't dislodge, fall or interfere with your freedom of movement? If in doubt leave stuff on the ground and haul them up with the help of a person on the ground or, if you're working alone, fill the bucket yourself.

Insurance claims, lawsuits and lost friendships are no substitute for safety.

Roles and responsibilities

As soon as you're not the only person on the team it is recommended that each person's role in the project be discussed in advance. Not every ham will follow direction, so be prepared. You can usually tolerate one such person in the crew but two or more is folly. The miscreant will almost always fall in line when the rest of the crew acts responsibly.

Take some care who you invite, or if you can't exclude some people you may want to assign them non-critical tasks where they're still involved and doing useful work. When no one will listen and each insists on doing whatever pops into their heads bad things will happen. Trust me on this. It comes from personal experience.

Those on the tower call the shots. They are the ones most at risk and also have the best view of the entire operation. The leader of the team (not always the station owner) cedes ultimate control the moment the climber's feet leave the ground.

Communication

To successfully work together as a team, even when everyone understands their job and behaves responsibly, it is necessary to communicate. Most of this is talk and some is hand signals. For example, when hoisting tower sections or yagis the person on the tower can use hand signals to tell the ground crew or equipment operator how to proceed throughout a procedure. Mistakes can easily result in injury (or worse) or damaged equipment.

For tall towers or when mechanical equipment makes talking unreliable use radios. Use simplex VHFor FRS/GRS handie-talkies. Headsets (with VOX) can be helpful provided care is taken that they cannot tangle in hazards. With ham equipment and non-ham personnel messages must be relayed, which is not ideal but can work. I have done this to work through a tower removal, with me on the tower and a professional operating the controls of a crane with a 110' boom.

Listen

There is a saying: when you look around at a group of people and decide that you're the smartest person there, you're wrong. Listening to the ideas and concerns of others can avoid a lot of grief. Many times you'll continue with the original plan but other times you will be handed a better way to proceed.

I recall years ago working on a tower with an older fellow I hadn't previously met to work on another ham's towers. We ran into a dilemma while trying to lift a new long-boom UHF yagi past obstructions. I was in the lead and described my plan to get the job done. He looked down and around and respectfully suggested an alternative based on his experience. I listened and realized his way was better. We got the job done without so much as a nick on those dozens of fragile UHF yagi elements.

Measure twice

While still on the ground you went through the antenna raising procedure in your head, keeping track of where every rope and element would be at each step. All seemed well. Now you're up the tower, the crew is in place and waiting for your signal to begin. Stop. Go through it all again, using the perspective from this vantage point. Look down and all around.

Will those long yagi elements really clear that inverted vee? When the yagi is rotated so that the clamp is facing the boom will the elements clear the yagi at the top of the mast? Do you have the correct fasteners stowed in your tool belt or pockets? Will that tree branch be a problem?

You should by now know the old saw: measure twice and cut once. It applies to antenna and tower work as well as in the workshop. Resist the urge to jump into things out of enthusiasm or a desire to not annoy your friends by your delay. The 30 or 60 seconds it takes is time well spent.

Plan B

It is very difficult to correctly visualize every eventuality in advance. Expect to deviate from your original plan. Or perhaps someone makes a mistake. Getting upset and simply pulling harder on the ropes isn't going to solve any problems, but it sure can make things worse. Much worse. It is times like these that mavericks among the team are most dangerous.

When things go wrong, stop! Antennas and tower sections can happily dangle in mid-air for a few minutes while you think things through and discuss with the rest of the team. Perhaps you need to pull a tree branch out of the way or cut it off. Other times it pays to lower the yagi to reposition tram lines or to temporarily move another antenna out of the way.

Some problems can be foreseen in advance. Whether plan B is conceived before or during the job you want to have it available. Discuss and listen. When you have a reasonable consensus put plan B into effect. Professionals always think ahead to what goes wrong. If they are part of the team you need to talk to them. Regardless of whether or not the hams have a plan B you can be sure that they do.

Clean up

Don't put this off. Immediately following completion of the work put all tools, equipment and parts in their proper container and then put the container in its place. Do this even if you expect to use an item again even as soon as the next day. To do anything less is an invitation to an accident or simply time lost looking for stuff. Leave the work site as you found it. Your friends won't miss you; they'll be working on their first beer.

Trust me, when you are positive you'll find that wrench tomorrow that you set aside today, you won't. Our memories are notoriously undependable. Habit and routine are your friends.

Post mortem

Things go wrong, they always do in any large or complex project. Learn from your mistakes, don't brush them aside or hide them. Review what went right and what went wrong. Keep the good and consider how to avoid the bad in future antenna work. Write it down if that will help you to remember.

Afterwards it can help to consult with more experienced hams (or professionals) to explain what happened and how they would do it better. Even if things did go right you might have just been lucky to avoid problems. Discuss those too. Never avoid an opportunity to learn.

None of us is perfect but we can always strive to do better next time.

Community building

Not only is working alone not recommended for safety reasons it avoids two important pleasures:

• Sharing time with our friends in the hobby through helping others and others helping us.
• Training the next generation of hams in tower and antenna work.

Too often hams keep to themselves. Reach out. There is a lot of pleasure in showing the ropes to others -- perhaps someone new to the hobby -- and passing on our knowledge. One day that person you helped out or educated will help you when you most need it.

Keep the (non-alcoholic) refreshments flowing throughout the work. Offer them a drinks or a meal afterwards, even though many won't stay -- they have their own lives to get back to. Thank every person who helped you out, even close friends and family. These simple gestures will be appreciated.

For us northern-hemisphere denizens there are several months ahead to pursue our goals, help others and spend time with our friends. Get to it.

Beverage Matching Transformer

I hope to experiment with Beverage antennas when/if I have enough land to build these simple and excellent low-band receive antennas. Since it's an easy matter to test some needed components on the bench I decided to order a few parts and get to work. This article is about my very first experiment: a matching transformer for a Beverage antenna.

I'll assume that readers know the characteristics and use of Beverage antennas, or at least how they're constructed, and perhaps even the theory of operation. There is ample material elsewhere, and I have several books and papers on my shelf that I've collected over the years. As always seems to be the case the most useful book for amateur radio use is ON4UN's Low-band DXing.

Matching requirements

The characteristic impedance of a Beverage is nominally 500 Ω. The true value depends on its length, height and ground quality, with a typical range between 450 Ω and 550 Ω. At the far end a (non-inductive) resistor of this value terminates the travelling wave from the reverse direction, ensuring no reflection and thus the maximum F/B. The transmission line connects to the near end.

Since we will be using a coaxial cable with a characteristic impedance of 50 or 75 Ω it is necessary to transform the Beverage impedance, approximately 10:1 or 6.5:1, respectively. This is typically done with a broadband transformer since the Beverage is inherently broadband; within reasonable frequency bounds there is no other tuning required on several bands, but with wavelength-dependent patterns. Transformers of 9:1 and 6:1 are typically used, which are easy to build and close enough to the ideal to be effective under most circumstances.

BN-73-202 specifications

There are a few options to construct the transformer. The antenna is only for reception so it can be small; power dissipation is not a concern. It is sufficient to focus on the transformer efficiency and impedance ratio. Efficiency can be important if a pre-amplifier is not employed to boost the Beverage's weak output (due to negative gain).

Building the transformer

I am no expert on ferrite cores and RF transformers. I rely on the recommendations of the experts. From the ample experimental data presented in ON4UN's book I chose the BN-73-202 binocular ferrite core. It is inexpensive and an excellent choice for the bands from 160 to 40 meters, where it is most likely to be used. Its only negative point from my perspective is its small size.

The core is rectangular and only slightly more than ½" long and wide. The holes are especially small, with a diameter of only 0.15". Small gauge wire is mandatory. This proved a challenge since the best design for my purpose requires a 3:1 turns ratio -- square the ratio to get the 9:1 impedance transformation -- with 2 turns for the 50 Ω winding and 6 turns for the 500 Ω winding.

I stripped the cover off some old telephone quad cable for the 4 insulated 22 AWG conductors it contains. The spec sheet linked to above includes a calculator for the length of wire required, included pigtails. I used 1" pigtails to ease interconnection in my test setup.

The two-turn winding was easy. The final four turns on the second winding were more difficult. When the wires are pulled through the holes they quite naturally arc toward the far wall of the hole midway through the core. These must be pressed down to make room for subsequent passes of the wire. I used a jeweller's screwdriver. Some care is needed to avoid damage to the wire insulation and core (ferrite will only tolerate a moderate amount of abuse before breaking).

Double check the number of windings when done since it's easy to lose count while fighting for space within those narrow holes. I know I did. Remember that there are two passes of the wire through the core in every winding turn. Use different coloured wires for the windings.

Testing the transformer

A selection from an of old stock 470 Ω carbon composition resistors serves as a facsimile of the Beverage impedance. I chose this value since carbon composition resistors tend to increase in value as they age. Measure the resistance before use. I chose one with a resistance of 505 Ω. It terminates the 6-turn winding.

The coax winding is directly connected to an antenna analyzer. That adapter with the wire jacks on one end and a BNC connector on the other is one I ordered from Elecraft at the time I purchased the KX3 at the end of 2012 when I first got back on the air. I no longer use a random wire antenna so it has found new life on my workbench.

As you can see the match is excellent at the high end of 160 meters, as it is elsewhere across the band. The stray reactance (inductive in this instance) is a combination of residual error in the analyzer, core and winding properties, and those pigtails plus resistor leads. How much they each contribute I cannot say.

The transformer is not for only 160 meters. It must also work well on 80 meters, and it would be nice if it worked on 40 meters as well. I adjusted the analyzer to plot R and X over the range 1 to 11 MHz. In the next photo you can see that the transformer is very flat right across all the bands from 160 to 30 meters. X remains so small that it doesn't visibly deviate from the zero line (however the scale is deceiving).

This confirms that I correctly built the transformer. I had little doubt that ON4UN or W8JI would lead me astray!

The impedance does depart from this excellent performance on higher bands. This is almost certainly due to the increasing contribution of the stray reactances in my test setup. These lengths of wire on 160 and 80 meters are tiny relative to wavelength. Not so as the frequency increases. When boxed for deployment the construction technique will be better.

Final

Clearly I need to improve my skill of winding transformers on these small binocular cores. What I did worked but is not recommended. For example, there is a danger of nicking the insulation on the wires when they are pulled hard against the resistance through the filled narrow holes. Ferrite is a ceramic matrix and ceramic is very hard and can easily cut plastic (or the coating on enamelled wire). Second, thin gauge wire will break when pulled too hard.

This experiment gave me confidence that I can construct the chokes and transformers I may need in the future. I have many more of these ferrite cores to experiment with, and I intend to do so. While I didn't time myself it took no more than an hour to acquire the wire, build the transformer, construct the test setup and make the measurements with the analyzer.

Don't be afraid to give this a try yourself. The materials are cheap and the results are very satisfying. Not many of us are in a position to put up Beverage antennas, but transformers of this type can be found in a variety of low-noise receive antennas and in QRP equipment. Similar transformers using much larger ferrite cores are used to handle a kilowatt when stacking yagis.

I learned to do something new and useful this weekend. That's time well spent.

Rolling Up the Radials

May is the end of 80 meter season. At least it is for me now that the weather has warmed and the grass is growing. Growing grass means mowing the lawn, an activity not entirely compatible with on-the-surface radials. According to my plan when I turned my ground-isolated tower into an 80 meter antenna the radials had to be removed in the spring. I'm not the only city dwelling ham following this seasonal ritual.

However I've not actually done that. The radials seem so settled into the turf that I experimented by doing the first mowing of the season with the radials in place. There was no hint of a problem. You can see in the picture how I stapled the radials at the tower base to keep them as low as possible. Wood made this easy. Their ends are secured with long nails, as pictured in the antenna article (link above).

I left the title of this article unchanged since I chose it before deciding not to remove the radials. Perhaps I'll leave the radials where they are for the time being with the hope of working a few stations on 80 during the upcoming CQ WPX CW contest.

Despite aborting the rolling up of the radials let's pretend that I did just that and that my 80 meter season is over. It mostly is finished in any case now that summer QRN has arrived, as have new man-made QRN sources that came with a couple of new neighbours and an LED lighting system included in one neighbour's renovation project. It's now a very attractive kitchen but those lights may explain the new QRN coming from the north. It is not only the low bands that are affected.

Retrospective

This is a good opportunity to look back on the winter low-band season that was. The low bands aren't easy for me with the strong local QRN on 80 and the impossibility of a highly efficient antenna on 80 and 160. Although I didn't have high expectations I did set objectives that seemed realistic at the time. In my judgment these modest objectives were largely met.

The highlights of my season on 80 include:

• 35 countries during CQ WW CW. Those multipliers helped lift me to world #2 SOAB QRP.
• Working VK0EK, Heard Island.

Not all went so well. There were also many disappointments:

• I did not reach DXCC. My count is 88 worked and 68 confirmed on LoTW. Although the antenna does not work all that well I very well could have made it to 100 if not for the QRN. This blight severely limited DX opportunities and QSOs during contests. As the saying goes: you can't work them if you can't hear them. Using a 40 meter inverted vee for receive helped a little, though not nearly enough.
• I expected better on 160 with this antenna. My worked count was below 20, and only 1 station worked in Europe (who answered my CQ!). Those 8 meter long radials are vastly inadequate.

What I do next on 80 will depend on my circumstances. If I keep this QTH I will improve the antenna. If I move I would like to build the parasitic array design from a previous article. A big question mark remains hovering over this dilemma.

Limits of modelling

NEC2, and even NEC4, do not accurately model near-field ground losses of ground-mounted vertical antennas. Many have noted this in both amateur and professional ranks. It's a fundamentally challenging problem. Experiments have often shown higher losses than those predicted.

Knowing this fact means that I can only try to further minimize ground loss by improvements in the radial system. This will not be easy. As a first step I will backtrack from my modelling adventures of last year and instead use fewer but longer radials: 4 x 20 meters. Since the available surface is 14 meters wide it is impossible to lay down a symmetric pattern of radials that long. Instead I'll take the 4 radials, start them out with a 90 separation and then run them along the property lines.

This is not ideal, for several reasons. First, 4 radials is inadequate. What I hope, based on my literature research, is that more of the return currents will be picked up with this arrangement, despite what NEC predicts. At least the longer radials should greatly improve 160 meter efficiency, even more than on 80.

Second, with a small number of radials it is difficult to equalize radial currents. Ground structure varies a lot, even over a short distance, and the ground depth on 80 and 160 is many meters. Unequal currents can reduce radial field effectiveness and make tuning of the vertical less predictable. That latter is easily remedied in the L-network.

Third, asymmetry and bending of the radials may reduce effectiveness. Based on what I've read on the subject this may be the least of my concerns. However it will limit my ability to increase the radial count with either short radials or long, straight ones since current inequality will be unavoidable. The short radials need not even be considered since they'll not carry any significant current in this arrangement.

It comes down to choosing the lesser evil. That's all I can hope to do unless and until I move.

Solar influences

Looking forward, the low bands will become increasingly important. Cycle 24 is forecast to end in 2020, with Cycle 25 beginning perhaps one year earlier. For the next 4 to 5 years the low bands -- 40, 80 and 160 meters -- are the places to be. Efficient, low angle radiators and directive, low noise receiving antennas are mandatory for DX and contest success.

If I don't move the prospects for amateur radio for the next several years are not promising. I don't want to be in that position. In setting priorities for my next station the low bands will loom large. Big antennas for 10 meters can wait a few years.

DXCC and Me

I am a DXer and a contester. Since contests are episodic and only a subset are of interest to me the bulk of my operating is DXing. Certainly I will rag chew, test antennas and more on the air, but it is the pursuit of DX, rare or otherwise, that keeps me walking into the shack every day. This has been true since my first QSO over 40 years ago. Even in contesting it is the DX contests that attract me more than any other.

With that background you may be surprised to learn that I have never applied for DXCC, nor do I have any plans to do so. My reasons are not negative ones; I have no complaint against the award and its many variations, or its pursuit by many hams. It's a fabulous award and is run with the utmost integrity and professionalism by the ARRL. They deserve the gratitude of the amateur radio community for the work they do with this award.

Those who enthusiastically pursue the DX side of our hobby can be roughly divided into several groups:

• Competition
• Magic of radio
• Awards

My DXing motivation is split between the first two, but not the last. I don't need or desire proof or other certification to feel validated or to enjoy my pursuit of DX. Even without the existence of DXCC I would still pursue DX much the same way. For many hams this is not the case; the pursuit of awards is the ultimate objective. Sometimes, it seems, beyond common decency.

As a example of the latter I'll draw your attention to the recent behaviour surrounding an aborted DXpedition to North Korea (P5). My intention is not to dwell on it, so if you want to learn more you can find it on your own. It is even quite easy to find the DXpedition leader's deleted complaint about funding woes.

For many hams around the world the pursuit of DXCC, and its apex the DXCC Honor Roll, are all consuming. It is the same kind of passion you'll find in recreational sports, fishing competitions, and endless other hobbies, not just amateur radio. It's a very human thing. Unfortunately that passion can inspire bad behaviour when it overrides common decency. Here are a few examples (I am sure you can think of a few more):

• Purchasing DXCC credit, even when failing to work the DX or not being logged accurately. On the other side of the transaction there are those selling confirmations, with or without a QSO, if only to attract funds to finance a DXpedition. There are even a very few who turn DXing into a business.
• There are some big amplifiers for sale. Very, very big amplifiers. There is a market for them.
• There are those who feel they are owed QSOs, regardless of their stations, abilities, sunspots or DXpedition objectives. That is, they feel entitled to what they desire. They make sure to let the DXpedition operators and sponsors (and all of us) how they feel when they don't get a QSO for every band-mode slot, confirmation is not forthcoming with minutes or hours, or the DXpedition is currently focussed on working a different part of the world.
• DQRM: For some it comes down to "if I can't work them (or don't want to) neither will you!"

It's very sad, even if it no longer upsets me the way it once did. Time and age bring perspective to all things. When I see these behaviours now I am more likely to shrug my shoulders and move on. There is no reason to let the angst of others infect my mood or joy in DXing.

So, if not awards, what does appeal to me about DXing? Why do I still pursue new countries and DXpeditions? Here are a few things. Some you will identify with, though probably not all.

The unexpected

I like to be surprised. Whether it's the kind of silly story I told earlier about youthful competition or calling CQ on a seemingly dead band to see who answers. I clearly remember the time over 40 years ago with my 807 transmitter and a dipole only 3 meters off the ground (really!) calling CQ on 20 CW one evening after school and being answered by an FO8. Or perhaps it's the magic of working a major DXpedition on 80 meters, unexpected with a small station like mine.

Even now, in a contest, as I rack up the QSOs running European stations I get a thrill when I am occasionally called by a relatively rare station in the Middle East, Africa or Asia. Or perhaps it's calling CQ on 15 in late evening when all is quiet on the band and being answered by a UA9 in their early morning.

The thing is it doesn't have to be particularly rare or unusual. It's the feeling of discovery. You can get it from just scanning the band, looking for DX and not bothering with the global spotting networks. A weak and watery signal emanates from the headphones and you are rivetted to the frequency until you find out where it's coming from. Is it rare or unusual in some way? That's all to the better, but even if mundane it's still fun.

This element of the unexpected is what attracts me to 6 meters. The openings are often so elusive and unpredictable that it can be difficult to step away from the shack. I would get the ominous feeling I might miss something. Years ago when I had a very good setup on 6 meters and I was alone in the house I would leave the receiver on 50.110 MHz hissing quietly in the background in the hope of a European opening. You learn to expect the unexpected.

Doing more with less

Easily working a rare one can be a bit of a let down. You make a couple of calls at the start of the DXpedition and surprise of surprises you get through. Then what? The joy of the pursuit quickly dissipates. What will keep you in front of radio then? Another band slot? Perhaps. You have to set your own objectives according to your interests.

Having a handicap can be add spice to the pursuit. Turn off the amp or even try QRP. Use a short vertical rather than a full size yagi. If none of that works you can always revert to power or a bigger antenna, if you have them. I find the pleasure of getting through is magnified when the odds are against me.

Skill

Efficiently navigating pile-ups and learning propagation patterns are only the start of the skills needed for DXing. There is also learning new modes, designing antennas, organizing station ergonomics, software configuration and much more. These are skills that do not require an interest in DXing but that drive to work DX spurs spending the time and effort to learn and hone our skills.

As we age there is a tendency to become sedentary, both in our minds and our bodies. This is undesirable, not only impacting our health but also sucking the spice out of our lives. Lifelong learning keeps us young. Every morning there is so much learning and doing to look forward to.

Antennas

If it were only for contests my interest in building a bigger station might be insufficient motivation to act. DXing nicely complements contests by making a competitive station useful every day of the year. A station built to be competitive in contests also opens DXing vistas impossible with a tri-bander on a stick.

Whether it is yagis up high, stacked yagis, 4-squares, low-noise receiving antennas, transmission lines or complex switching systems, all contribute to DX success. So, as readers of this blog have seen, my antenna design focus over the past months has shifted from the small to the large. The hard work begins when the antennas are built. That can't happen until I have the land for it. DXing increases my motivation to move forward on this plan.

Volume

It is not only the rareness or uniqueness of DX that appeals to me. Quantity also matters. There is joy in filling a contest log with thousands of DX QSOs. To those who dislike contests or just don't see the point this may seem like mindless drudgery. It's not. Apart from paying dividends in contest scores and ranking, for the DX enthusiast the ability to work so much DX in a short period of time is fun in itself. Rareness is nice but so is lots of non-rare DX.

There is always time outside of contests to pursue longer conversations with DX stations or to work DXpeditions. There is even the thrill of volume outside of contests. It is common to hear those with large stations casually running DX every day. For the DXer this is a fun way to get more value out of the stations they've invested in -- after all, there really aren't all that many major contests throughout the year.

There is even the potentially greater thrill of helping others to fill their logs with DX. Consider that when you work a DX station the perspective is reciprocal: they, too, are working DX. By working many stations you are helping them enjoy their DXing pursuit. Most hams have small stations and appreciate the opportunity to work stations far away. Luck and good propagation is needed for two small station on opposite sides of the planet to hook up, but when one station has a big signal it becomes much easier for everyone.

Maintaining perspective

DXing for me is a little like love: often the pursuit is more rewarding than the catching. This is why I got an unanticipated thrill of working QRP for a couple of years, because it made the pursuit last longer and increased my enjoyment of operating.

If I don't get through to work a DXpedition on some band or even at all there's always next time. That is, I do not get irritated, frustrated or worried when I fail to get through, even for an ATNO (all time new one). There are always more skills to learn and antennas to design and build. One day there will be another DXpedition to the same locale and, hopefully, I'll be better prepared to get through.

I will probably never achieve DXCC Honor Roll, or at least the required confirmed entities (especially if I continue to not apply for DXCC). For difficult paths I may be unwilling to sit on the radio for the length of time needed to get a good shot of making a QSO. Other times I would really rather go outside and enjoy the sunshine during our brief summers. Working the rare ones is great, and I love it when I do, but not to the exclusion of everything else.

My "modern era"

My all time total is over 300 countries, though I do not know the exact number. I reached that milestone by 1992 when I chose to go QRT for 20 years. I had no interest at all in continuing from that count when I renewed my activity in early 2013. There were so many changes in the world and the DXCC list that I did not find it meaningful, or work the effort to tabulate all those cards and adjusted country affiliations. So I started anew, and I did so with QRP. I did well.

Now after 3 years of activity in my "modern era" I have 271 worked (225 with 10 watts or less) and 242 confirmed on LoTW (logbook of the world). I don't count the paper cards I receive since I can't be bothered to do the work. That alone should tell you where I'm coming from: more operating, less paperwork.

The one great thing I like about DXing today is LoTW confirmations, which removes the time and trouble of pursuing paper QSL cards. Also valuable are all the on-line logs which allow me to quickly know that my QSOs are confirmed. There is no more waiting a year (or two or three) for a card to come back to me saying: "sorry, you're not in the log."

My current run of DXing activity is likely to run until the end or until I am too old and feeble to maintain a house and antenna farm. I am confident that this time around I won't lose interest in the hobby. There is always more DX to work, rare or otherwise, on one band or another. Even during the coming solar minimum.

Adding 160 to the 80 Meter Vertical Parasitic Array

My earlier article describing a model for a 3-element, 4-direction vertical yagi for 80 meters includes a provision for an omni-directional 160 meter vertical. I chose not to fully develop that aspect of the antenna at that time since it is deserving of a separate and comprehensive treatment of its own. That time has now come.

You ought to read that article before proceeding since I will not repeat much about the physical layout and construction of that antenna. That background is vital to reading the present article. I will assume that you have read it.

My objectives

I am not one of the great enthusiasts for 160 meters. The DX challenge intrigues me since I have never had an opportunity to build and use a good antenna for this band, nor have I been in a sufficiently low noise environment to even want to try. Perhaps my enthusiasm will grow, or perhaps not. For the present my objectives are modest.

First, I want to enhance my contest scores with QSOs and multipliers on 160. Second, I would like to achieve DXCC on 160. Both are attainable with a modest antenna. High power would also help, however doing so with 100 watts is an attractive option, if only for the challenge. After all, 10 db of amplification can cover for a poor antenna, but I want to make an antenna that is as good as possible without extreme effort.

If you've followed this blog for any length of time you'll know that designing and building antennas is something I like to do. Getting around that with an amplifier doesn't satisfy me. Going to high power is something to do after the antenna works to my satisfaction.

Alternative approaches

There are basically 3 alternatives to extending the 80 meter antenna to 160 meters, to convert what is a λ/8 vertical to an electrical λ/4. The support structure for the 80 meter parasitic elements includes an additional 6 or 7 meters of mast and a wire top hat incorporated into the catenaries. Additional loading may also be required since the mast and top hat will not be adjustable once built.

• Top relay: A high-voltage vacuum relay at the top of the 80 meter vertical switches in the additional mast and top hat for 160 meter operation.
• Trap: Placed at the top of the 80 meter vertical it allows a fully passive approach to adding 160 meters. However there are costs, on both bands, that need to be considered.
• Parallel wire: Run a separate wire parallel to the tower and attached to the extended mast. A switch at the feed point selects the tower (80 meters) or wire (160 meters). This is the one pictured in the article describing the 80 meter array. There are switching and coupling issues to be considered.

The radial field for the 80 meter array will initially serve for 160 meters. Although the diameter of the field is ~55 meter it is dense enough to allow for good, not great, efficiency on 160. The ground impedance will be higher than on 80. On 160 it will be electrically short so the radiation resistance will be reduced, which will also impact efficiency.

With all the alternatives I want an acceptable match to 50 Ω without the need for a matching network, just as for the 80 meter array in omni-directional mode. The switching system required for 80 meters direction and mode, and for band selection is as complex as I want. That is, more switching requirements for an L-network or 160 meter band segment are undesirable.

These constraints versus performance are acceptable to me, at least for the near future. I can revisit 160 after the rest of my next antenna farm has been built. This is in accord with my priorities.

I will now run through the presented options to see how they compare. All can work well with careful design. My overriding concern is to sustain excellent 80 meter performance and operational band width, and make sacrifices on 160 if necessary.

Basic model

Before going further it will help to go over the common aspects of the modelling. The 80 meter vertical is 20 meters tall, just as it was before. My objective is that the vertical in omni-directional mode require no matching network. If not for that a precise vertical height would be unnecessary since this would be compensated for in the L-network without affecting array operation.

The extension mast begin slightly above the 80 meter vertical, just enough to convince NEC2 that it is not connected to the 80 meter mast. As previously described the 80 meter vertical is a tower of 250 mm effective diameter and about 19 meters tall, with an adjustable mast to tune it to resonance. The two masts are mechanically coupled with a structural dielectric rod such as fibreglass.

A short adjustable spire projecting above 27 meters is included in the model, but may not be required. Once built the spire is too far out of reach for tuning.

The extension for 160 meters is as shown in the physical layout of the earlier article. What I've now done is make the extension mast and top hat explicit in the model. The mast extends to 27 meters height and the four top hat wires are 5 meters long. These wires should be copper-clad steel (available from many suppliers) rather than copper (hard or soft drawn) since they are under enough tension to stretch over time, and possibly break when the mast is subjected to high winds and icing. Alternatively the catenaries can be entirely rope, with copper wire running along the rope. The ends of the wires should still be looped around an egg insulator to avoid excess corona effect which could alter antenna resonance when the rope is wet.

Per this design the full vertical is resonant at ~2.150 MHz. A coil of 20 μH at the base of the mast extension (height of 21 meters) brings resonance down to 1.85 MHz. The coil value is convenient since I have one of just about that value in my junk box, reclaimed from the half sloper I removed last year.

A smaller coil is easily possible with a taller spire or longer wires in the top hat. Those were avoided in order to minimize the risk of interaction on 80 meters; that is, the isolated 160 mast and top hat accidentally interacting with the 80 meter array, which is the more important of the two antennas. The model shows negligible interaction. I may eventually try a redesign with longer top hat wires, just to see what happens.

The radial field of the 80 meter array mostly fills a square 55 meters on a side. This is on the small size for 160 meters, which out to be closer to 40 meters length (λ/4). For this reason in the MiniNEC ground I modelled the ground resistance as 10 Ω on 160. This may be a bit higher than the actuality, though that will also depend on ground quality. I assume EZNEC medium ground. In this case the near field ground loss is -1.7 db. For a 5 Ω ground the loss is -0.9 db.

The SWR band width is reasonably good, and could be made better with an L-network (or higher ground loss!). The L-network design is straight-forward, and can be done once the antenna is built and the impedance measured. The R component of the impedance is the sum of the radiation resistance and loss resistance, so it is easy to see how the impedance is expected to vary with the ground loss. Expect seasonal changes.

Top relay

The antenna design is really just what I've already described above for the basic model, with the addition of a SPST relay at the top of the 80 meter antenna to connect it to the extension mast, loading coil and top hat for 160 meter operation. Even so there are practical considerations in building the antenna.

No ordinary relay can be used in this application. The RF voltage can be very high at the top of a vertical (or the end of a dipole) even with moderate power. That point is very high impedance, which means close to zero current and high voltage: Z = E / I. It cannot reach infinity since there is always a conduction path in air and over the contaminated (dirty) surface of the end insulator. A large conductor reduces the maximum voltage, which is why some place a metal ball at the top of a vertical to reduce corona discharges. In some circumstances it can even reduce the noise floor on receive.

A vacuum relay is a required. This is stressed in ON4UN's Low-Band Dxing book for good reason. Even so it is possible to encounter difficulty. It can help to place a small capacity hat at the top of the 80 meter vertical to reduce the voltage at the relay. This can be as simple as a 1 meter long rod centred on the vertical element.We don't want to load the vertical. just move the high voltage pont from the vertical apex to the ends of the rods.

The other consideration is the wires carrying power to the relay. Run this inside the tower, with spacers to get some separation from the metal structure, to reduce its mutual coupling to the vertical. Chokes may also be required at both ends of the cable. Do not use the tower as a DC return path; always use a separate wire pair.

Trap

This seems to be the simplest and most convenient solution. After all, no extra switching of any sort is required to operate on both 80 and 160 when the array is in omni-directional mode. Unfortunately it doesn't work as well as one might hope.

Traps are not perfect filters that block some frequencies and let other pass. No matter how they are tuned traps introduce reactance. Typically this requires lengthening of the element inside the traps (on the band the trap is designed to block) and shortening of the element outside the traps (the lower frequency band that passes through the trap). Worse, the reactance changes with frequency and therefore increases antenna Q on 80 meters, and may do so on 160 meters.

That is what I found. Whether the trap is tuned above, within or below the 80 meter band (3.5 to 3.8 MHz in this particular antenna) or the L/C ratio the SWR band width is reduced.

The 80 meter portion of the vertical must be lengthened ~2 meters. Alternatively an L-network can be inserted in omni-directional mode and the existing L-network for directional mode can be adjusted. Gain and F/B of the 80 meter array are little affected by the use of a trap: gain reduction is approximately -0.1 db and F/B is 2 to 3 db better at the low end of the segment.

The model view of the antenna shown above is for this alternative construction. Notice that on 80 meters significant current flows beyond the trap. This is by design.

SWR of the trap 80 meter vertical array in omni-directional mode, of length 23 meters (to the trap)

By careful choice of trap the loading coil for 160 can be eliminated. For example, tuning the trap for 3.9 MHz (L=8.2 μH; C=240 pf, X=200 Ω). I found these values entirely by accident during modelling. The trap exhibits inductive reactance on frequencies below trap resonance, which is typical for traps.

When in directional mode on 80 meters the L-network must be changed to accommodate the change in electrical length of the antenna due to the trap. The revised values are a series coil of 2.1 μH and a 830 pf capacitance shunt across the transmission line port. In practice it will be necessary to design the network after construction by measuring the impedance to be transformed.

The resulting SWR in directional mode is barely acceptable (compare to the SWR in the earlier article). Low SWR cannot be readily achieved when a trap is used.

Parallel wire

This approach is similar to the top relay option but moves the relay to the bottom. This placement is not only more convenient a conventional relay can be used since the voltage is low.

Of concern is mutual coupling between the parallel wire and the 80 meter vertical. The wire is switched at the feed point, run parallel to the tower and attached to the mast extension. Additional loading can be added as required.

In the model the wire is placed 1 meter from the tower axis, running from 1 meter height to 20 meters. From there it angles upward to connect to the bottom of the mast extension. At the bottom the wire runs tangent to the tower for 1 meter then straight down to ground through a 10 Ω resistor. The resistance is the estimated equivalent ground resistance (MiniNEC ground). The model doesn't allow the bottom wire to enter the tower area (to the switch box), which is why it is run at a tangent. The model accuracy impact of doing this is negligible.

The model view with current plot is for 1.85 MHz. Notice that there is some current induced on the tower even though it is λ/8 on 160. There is no difference whether the tower remains in-circuit or is floating. The parasitic elements carry negligible current, which is ideal. Even so it is likely best to float the tower and all parasites to simplify the switching matrix.

To my surprise there was no need for a loading coil between wire and extension mast; it resonated very nicely as is. However the radiation resistance is a little low, lower than the case for switch option, probably due to the tower coupling. An L-network is advisable for maximum low SWR band width.

The current flowing out of the main array volume
reduces directional mode performance on 80 meters

Unfortunately we now run into difficulty. On 80 meters the presence of the 160 meter wire severely affects operation, in both omni-directional and directional modes. The 160 wire, floated or grounded, combined with the extension mast and top hat carries significant current. Most of the problem is due to the amount of current carried high above the 80 meter array which reduces directional performance (gain and F/B). A change in the L-network easily tames the driven element impedance.

A relay can be used at the top of the wire to break the resonance, with the same requirement for a vacuum relay as with the top relay option. Opening the relay and floating the wire bottom breaks the resonance and restores 80 meter performance. The L-network will still require some adjustment to compensate for wire coupling. Keep that in mind if the 160 meter wire is added after the 80 meter antenna is tuned.

Or...keep it simple

An alternative not mentioned is to forgo use of the extension mast and top hat on 160 and simply use the tower as-is for 160. Obviously it is far from resonance since it is only λ/8 long on that band. An L-network at the base, with or without a loading coil at the base, can match the 20 meter tall tower.

The reasons I am not considering this alternative are twofold:

• Efficiency: There will be matching network loss and increased ground loss due to the very low radiation resistance of ~7 Ω. Although I am not initially aiming for the ultimate in a vertical for 160 this goes too far in the wrong direction.
• Exploit the mast: Even without considering 160 meters there is still a metal extension mast in my 80 meter array design so that the wire parasitic elements can be full height rather than top-loaded with diagonal T's. I want to push 80 meter performance rather than compromise.

That's my rationale. Others may want to consider this option, and accept the compromise. It's a matter of choosing what best fits one's circumstances.

Conclusions

For my purposes the trap option must be eliminated due to its negative impact on 80 meter performance. This leaves either the top relay or parallel wire options. Both are similar in that a relay is needed at the top of the tower. Even though the wire tip voltage is lower than in the case of the top relay option a vacuum relay is still recommended to better isolate the wire from the extension mast for any induced current on the wire.

My preliminary conclusion is to go with the parallel wire option. It is likely more reliable than a top relay, which must operate at high voltage, and has the same negligible impact on 80 meter performance when the wire is switched out at both top and bottom ends. If a loading coil can indeed be eliminated, all the better.

There is still the matter of suitably isolating the relay wires running up to the top relay so that it doesn't act as part of the antenna, on either band. Since it isn't possible to model the relay wire pair running inside the tower (one conductor within another) I will have to rely on the experience of others and on-site measurements during construction.