Wednesday, March 25, 2015

Buying a Used Yagi: Hams Ripping Off Hams

I described my research into choosing a tri-band yagi in a series of articles last year (2014). The antenna I eventually purchased was not the first one I looked at. Originally I preferred to locate a TH3 since that seemed ideal to my needs and tower capacity. The Explorer 14 I bought has the same boom length and more efficiency (4 less traps) but more wind load.

While shopping for a TH3 I encountered something unfortunate. There was a transaction involving an antenna where, in my opinion, one ham ripped off another. That story is the subject of this article. No calls or names are mentioned, and indeed I don't know the identities of certain parties. While stories like this are atypical in the ham community, fraud and frayed relationships sometimes just seem to happen when money is involved.


I found a TH3 on the local used market and contacted the seller. He explained he didn't know much about antennas, especially yagis, and would willing to negotiate the already reasonable asking price. I drove over to have a look. Problems were already evident from the ground, which is not a good sign. For example, one element tip dipped downward from the outermost trap.

I climbed the tower for a closer look. More problems appeared. He wanted the antenna down and since he was a decent fellow I gladly performed that small task for him. It was already becoming clear to both of us that I would not buy the antenna.

With the antenna on the ground I began to disassemble it. It quickly turned into something like a forensic analysis at a crime scene. What I found shocked both of us. He soon realized he'd been had by the ham who sold it to him.

How we got here

Someone he connected with in a local club offered to sell him a yagi when he was looking for something small and inexpensive to work some DX on the higher HF bands. That individual was friendly and willing to help put the antenna on his tower. A deal was negotiated.

The seller delivered the antenna and assembled it. In retrospect the buyer realized he should have been suspicious since the antenna looked odd and the seller gave him no opportunity to consult the manual that he'd downloaded in advance. He quite sensibly wanted to make measurements and just to have a closer inspection of his first HF yagi. The seller explained he was pressed for time and wanted to be quick with the job. So up the antenna went and coax attached.

Signals were heard and the transmitter seemed happy. Money changed hands. But it was soon clear that not all was as it should be. The SWR was quite high in many places. When contacted the seller told him that was nothing unusual and just to use the rig's ATU to match.

He had no basis for comparison and so could not check gain and I don't believe he checked the F/B. He only knew that when he turned the antenna the desired signal peaked and he was usually able to get through. Of course even a dipole shows directivity, and a yagi is like a dipole in its basic azimuth behaviour: broadside gain and a null off the sides.

This is a real story and a real antenna so I am able to provide physical evidence. You'll soon see why I was outraged by what had transpired.

Busted trap

The cause of the dipping element tip was discovered when the mass of tape holding the tube to the 15 meter trap was removed and the trap opened.

Pretty, eh? The plastic coil form is severed and the tab connecting the trap shell (capacitor) to the element was sheared off. The stand-off toroidal insulators are heavily scored. A violent impact would account for this degree of damage.

Trap covers

All the trap end covers are taped. The few I uncovered were severely damaged by UV radiation. This is a case of the shutting the barn door after the horse has bolted. Tape (the necessity of which is debatable) should have gone on earlier to reduce sun exposure.

The decay of one cover was so bad that the tape was actually holding the cover together. In another case removal of the tape revealed an ill-fitting plastic plumbing cap rather than a Hy-Gain part. Hy-Gain sells replacement kits which are reasonably priced. There really is no excuse for what I found.

Parts substitution

One tube joint could not be taken apart. There wasn't even a clamp at the joint. A closer look (see upper right of above photo) showed no compression slots in the larger tube and that the tube was not square cut. This is a press fit that was likely seized by corrosion or an oversize wall in the larger tube.

I can only presume the original tube was damaged beyond repair and replaced by another tube that was not properly selected or prepared.

Hy-Gain multi-band yagis have few trap varieties. This is good design and good business. All the 10 meter traps are identical. The 15 meter traps are different for the driven and parasitic elements. This allows kilowatt power without heating the driven element traps to destruction. In a conventional yagi the driven element current is higher than the parasitic elements. These traps are wound with copper wire to reduce resistance and therefore I²R loss. All the other traps are wound with cheaper aluminum wire.

The difference can only be discerned by the part number printed on the affixed label (too faded to read in the present case) or by peering through the drip holes to inspect the wire colour. The wire in the trap wound with copper should be brownish instead of silvery gray.

Element-to-boom clamps

I found two cases of substitution of proper Hy-Gain parts. Have a look at the adjacent picture.

On the left is a clamp made from half of the correct part and half that homemade from sheet aluminum.

First, the alloy is unknown and therefore of uncertain strength. Second, it is improperly shaped. The tubes inserted in this clamp had their ends severely crushed.

Why someone go through so much misspent effort when a replacement part is readily available and inexpensive is mystifying. I can only imagine that it was someone with more time on their hands than good sense.

On the right is the clamp for the driven element. This clamp must be larger to accommodate the plastic inserts which insulate the driven element from the boom. This is needed for the beta match feed. Except I found that the wrong clamp was used. To get a compression fit to the boom the clamp had to be tightened so much that the plastic inserts were crushed and split (not visible in the photo). Further, the anti-rotation set screws were replaced with longer hardware to bridge the gap.


The TH3 boom is a little over 4 meters (14') long. It comes in 2 identical halves that are joined at the centre with a clamp.

The ends of the two halves (off the left side of the photo) are aligned. It is readily apparent their lengths are unequal. The longer is the correct length for this antenna. The other must have come from another antenna since it shows no signs of having been cut. My guess is that it is from a TH3jr (12' boom) since the length is correct for that antenna.It would also explain the lack of copper-wound 15 meter traps in the driven element. That is, this antenna may be a mix of parts from multiple antennas.

Not only is the resulting antenna physically unbalanced the tuning of the elements will be sub-optimal for the altered inter-element spacing. The result will be poorer performance and SWR behaviour. Even if the difference is small it makes no sense to put up a 3-element yagi that and not get the performance you paid for.

Notice the deep indentations in the longer boom half. It's worse than it appears in the photo. Similar damage is present at the position of every boom-to-element clamp. The set screws (2 per clamp, to help prevent element rotation) were overtightened, in a few cases piercing the boom wall. There are more dimples than set screws which tells me that this antenna was improperly assembled at least twice, with the boom partially rotated the second (or third) time.

Although this is not a large antenna there is no excuse for this abuse, which will reduce survivability in severe weather.


On a somewhat positive note most of the hardware -- hose clamps, bolts, washers and nuts -- were stainless steel. However the sizes were often incorrect. This is the best I can do to say something positive.


There is great fellowship among radio amateurs. We help each other out with antenna-raising parties, sharing expertise and software, advice and training, and even simply offering pointers to help out the novices among us. Elmers -- those hams who mentor others before and after they first join our ranks -- are rightly venerated.

Yet hams are only human. It is a mistake to imagine that we are all cut from better cloth. Just as in the general population we have our misfits, anti-social miscreants and worse. The number in the latter group is small but can have devastating impact when they prey among the novices in our hobby or those who are overly trusting of fellow hams.

We like to believe we are good judges of character. It is not so easy, though it can become easier as we grow older and wiser, often by the "benefit" of bad experiences. Getting ripped off not only cost time and money it can also cause acute embarrassment. I have seen disputes come close to fisticuffs in flea markets. I have looked sellers in the eye and asked hard questions about an item they were selling, and then watched them squirm. Even the dishonest have consciences and you may see it on their faces.

Too often we keep those incidents quiet, fearing that other will think us foolish. That can be a mistake, one that the criminal class counts on for the continuation of their careers. Perhaps my story can, in a small way, shed some light where it's often absent.

In any transaction where you lack expertise about a product or don't know what question to ask, bring a knowledgable friend along. It won't hurt and it can help avert a bad experience. When we lean on each other we are all stronger. Pass along the same favour when you have a chance. Just don't go overboard and become suspicious of everyone; happily the bad apples are the exception not the rule.

Thursday, March 19, 2015

Radial Topology Options: 2-element Parasitic Vertical Array for 80

In this article I want to look further at radial topology of vertical arrays for the low bands. In an earlier article I looked at the impacts of base height and radial arrangement of an above-ground mount for a 2-element vertical (ground plane) array on 40 meters, one that had 4 radials per element. That antenna performed well in the model, although I did note the potential pitfalls regarding the precise way in which the radials interlace, parasite tuning and the expectations for ground loss that may differ in the real world.

Although doing that model on 40 meters makes the antenna more mechanically friendly there are better alternatives for gain, directivity and low radiation angle on that band, such as a small yagi that is 20 or more meters high. So it was perhaps more of a modelling convenience than a desirable antenna project. On the other hand, hams without large towers and a disinterest in large yagis have used vertical arrays, including 4-squares, on 40 to good effect.

Dropping down to 80 meters and the situation is markedly different. Even among the big guns of the world a yagi is rare and raised vertical arrays are, while not rare, not common either. Ground-mounted vertical arrays are more typical, with the 4-square being pretty much the big-gun standard.

Standard element

The vertical element I will use here is a ground-mounted monopole tuned to resonance (X = 0) at 3.6 MHz over EZNEC medium ground (0.005, 13):
Top view of vertical; wire 1 is the vertical monopole
  • Monopole is 20.2 meters long and 50 mm diameter aluminum, fed at the bottommost wire segment. The chosen diameter is an average value assuming a tapering schedule for telescoping aluminum tubes.
  • Radials are 20 meters long, 16 AWG aluminum wire. This is commonly available and economical electric fence wire.
  • There are 16 radials. This quantity is a compromise among computation time, ground loss reduction and NEC2 model reliability.
  • Mounted at a height of 10 cm, which is just above the 0.001λ minimum W7EL recommends for reliable NEC2 emulation of radials lying on the ground.
  • Use of a common mode choke at the feed point and other places is assumed in order to remove the need to model common mode current on the outside of the transmission line. Burying the coax does not eliminate this requirement.
At resonance the antenna has a feed point resistance of 37.6 Ω with a broad SWR bandwidth that is a good match to 50 Ω coax. Its gain is -0.7 dbi at an elevation angle of 15°. This is pretty typical performance for a vertical of this type.

I have chosen 15° as the comparison standard for 80 meters since that is a median value for medium length DX paths, which are the most productive on this band. The longest paths can have angles well below 10°, though not always. Since low angles are the most difficult to attain and are needed to best DX results and high angles are easy with a second, horizontal antenna I choose suitably low angles as the standard of comparison in the majority of my models. In my many articles about 40 meters antennas I used 10°, and lower angles for progressively higher bands.

Adding a second element

I will continue with λ/4 element spacing, which on 80 meters places the identical second element at 21 meters distance. The optimum spacing may be different though, I expect, not by much. My interest here is to evaluate radial topologies. Optimization can be performed later, should one of these arrays be built.

The parasite will be a reflector element. As we'll see identical elements work well to achieve the desired effect in this configuration. Switching between either end-fire directions is straight-forward, being no more difficult than for the design I proposed for the 40 meters array.

With 21 meters spacing and 20 meter long radials the two radial systems overlap. We have a few strategies to deal with this:
  • Place one radial field above the other, allowing capacitive coupling between them. Doing so can require making the parasite a reflector since there is near-critical coupling between elements when the height separation is small.
  • Lay them in the same plane with electrical continuity where radials cross. This is sometimes done in 4-squares and similar arrays though there is limited benefit in extending radials further than the first crossing. It is usually better to use the extra wire to make a mesh ground plane at the monopole base to reduce near-field ground loss.
  • As above but terminate the radials at the first crossing.
I built models for the first and third cases, rejecting the second since it is mostly redundant to the third.

Overlapping, capacitance-coupled radials

The most critical parameter of a Moxon antenna is the distance between the turned-in ends of two elements. That is where the capacitive coupling is strongest since that is where voltage is highest.

Strong coupling drives the parasite current higher than in a conventional yagi. It also restricts the phase relationship between the elements such that above a critical level of coupling the parasite can only operate as a reflector element. This is why I commented in my earlier article on the 2-element ground plane model that it is sensitive to precise placement of the (interlaced) radials.

As I noted above when the second element is added to make a 2-element ground-mounted vertical array the radial systems must be vertically separated and the amount of separation is a critical parameter, as in any critically-coupled array. I modelled the array with a range of separations, each small enough that the vertical offset of the monopoles would not significantly alter the far-field pattern.

With a 10 cm (4") separation (driven element on the right is 20 cm above ground) I achieved the best performance. However I did not try to fully optimize the array: my aim is to generally characterize the array to decide on whether its merits motivate further investigation.

Wire currents at 3.6 MHz, 10 cm radial separation; reflector at left

To demonstrate radial/element coupling I have plotted the modelled currents on the array's top view. The driven element current is normalized at 1 A. The driven element is to the right (red) and the reflector is to the left (blue). Radial currents are roughly maximum about 2 meters out from the monopole: the ground's dielectric constant makes the 20 meter long radials electrical length slightly more than 0.25λ. Strong coupling is evident in the high current in the parasite monopole: 70% that of the driven element at 3.6 MHz. It only appreciably declines when the radial system separation grows to at least 30 cm (12").

Radial currents are not close to equal or sum to that of their respective monopoles. Currents are higher where a radial crosses another, and highest where the far end of a radial is close to another radial. Only where a radial stands clear is the current close to the theoretical 1/16 of the monopole current. It should be evident that radial placement is critical to antenna performance, as it was in the 2-element ground plane.

The forward gain at 3.6 MHz is  about 4 db more than the single element at an elevation angle of 15°. Relative gain of 4.2 db is maximum at 3.5 MHz, and slowly declines to 2.2 db at 3.8 MHz. F/B is poor, ranging from 8.4 db at 3.5 MHz to 9.7 db at 3.8 MHz, and reaching a maximum of 10.9 db at 3.7 MHz.

The SWR is surprisingly good, staying below 2 over most of the band of interest to DXers and contesters. Unlike conventional parasitic arrays the SWR bandwidth is excellent and a good 50 Ω match. The change in SWR with frequency is mostly due to the feed point resistance since the reactance changes more slowly.

Increasing the radial system separation to 20 cm leaves the SWR and F/B nearly unchanged. However the gain at 3.5 Mhz is 1 db lower and the frequency of maximum gain rises to 3.6 Mhz. Even a small change in radial coupling can have a significant effect.

For a simple antenna on which I spent so little time this is good performance. But it comes with some important catches:
  • Maintaining the required radial field separation is difficult. Not only is it mechanically challenging it is a safety hazard to have 20 meter long wires 10 cm above ground, whether for pets or wildlife that will inevitably wander into the area. The radials, if bare wire, must never touch any other.
  • Weather will alter radial coupling. Winters with snow and ice will almost certainly destroy the radial behaviour, and the structural integrity of the raised radials.
  • The antenna is very sensitive to changes in radial coupling. Those changes are usually for the worse.
The study of this radial topology has been interesting and instructive. Since it is not promising for an 80 meters vertical array it is time to move on to the second case.

Radials tied at the mid-point

Terminating and tying radials of adjacent verticals in an array is an old idea, and has been used in commercial broadcast arrays for years. It is also an obvious one, so that it is unsurprising that I independently thought of it before discovering it in the literature. In the amateur field you can read, for example, a discussion by the late W4RNL (Cebik).

There is some coupling in this array, mostly between radials whose ends are close together. However this is dominated by monopole coupling and direct connection of the radial systems. At first blush this would appear to be an array more suited to having all elements driven, with a power splitting and phasing system to achieve the desired result. Antennas such as 4-squares are of this type, though so are 2-element end-fire arrays such as described here.

Connected radial; reflector (blue), drive (red), connected pairs (black)

The radial currents (defined above) vary less than in the array with overlapping radials. First, the reflector current is 58% that of the driven element, which is lower than with overlapping radials though still more than in a conventional yagi. The sums of the radial current for each element are roughly equal to that of the monopole, approaching the ideal situation of a single element where radial currents are equal and sum to that of the monopole (assuming radials lengths near 0.025λ).

Radials that had been capacitance coupled are now directly connected: 16-21, 15-22, 14-23, 13-24 and 12-25. While the currents in these radial pairs are (necessarily) equal where they connect it may seem surprising that currents are quite different at their origins. Power is flowing between the elements, but with a 133° phase difference (at the radial origins). Current nodes occur on driven element side of the radial pairs, closer to the driven element where the current differential is greatest. On wire #23 the node is adjacent to the radial origin (driven element monopole junction).

Despite the relative lack of control over parasite current and phase this array has gain and F/B. However performance is not quite as good as the array with overlapping radials. Nevertheless this is a more realizable antenna since the radials can all be on or just below ground, and coupling requires less fine tuning.

Since the elevation pattern is indistinguishable from the one above I will instead show the azimuth pattern, which is also the same. The plot is at right.

Maximum gain is 2.82 dbi at 3.575 MHz and 15° elevation, which is 3.52 db better than a single vertical. At 3.5 MHz the relative gain is 3.2 db. Going higher, relative gain gradually declines to 2.9 db at 3.8 MHz. F/B is poor. Its maximum is 9.8 db at 3.8 MHz, and an especially bad 3.5 db at 3.5 MHz.

Although I have spoken against the importance of high F/B, particularly for the high bands in a small station with a single yagi, the situation is different on 80 and 160. The bigger problem here is QRN, not QRM. Directivity is needed to improve SNR enough to copy DX stations. If this antenna is built it ought to be supplemented with a low-noise receiving antenna such as a Beverage or compact, rotatable loop. Otherwise be prepare to not hear many stations that call you, especially if you run a kilowatt.

SWR is sufficiently broadband to allow no-tuner use from 3.5 MHz to 3.8 MHz. The above SWR plot is for equal height monopoles (identical elements). This worked well in the array with overlapping radials, though here the resonant frequency drops a little lower than is ideal. A 2,500 pf capacitor should be switched in series with the driven element to bring the SWR below 2 across this frequency range. The value isn't critical, 2,200 pf or 2,700 standard values can be used, but use a ceramic knob capacitor if possible to reduce loss (and potential failure when running a kilowatt).

My take on this antenna:
  • It has the makings of a good, simple, broadband switchable gain array without the burden of a power-splitting and phasing system. Even a commercial product to perform these tasks requires work to tune and match the elements and adjust array performance.
  • F/B is so bad that a high-directivity receiving antenna be seriously considered.
  • Altering the radial quantity and length will change array behaviour. Model first before adding radials to reduce ground loss, since wire lengths may need adjustment.
Again, this is an experimental model and not a design to be rushed into construction without further evaluation.

Disconnecting the common radials

As a final experiment in this phase of modelling 2-element parasitic vertical arrays I will take the previous design and disconnect the 5 radials pairs that are joined at the midpoint between elements. My aim is to see how much capacitive coupling can be achieved and whether it can be used to raise parasite current and thus hopefully improve F/B without the tribulations of overlapping radial systems.

I modified the connected radials model by disconnected the 5 pairs of connected radials and various the separation distance. The results were disappointing. Mutual coupling between elements was low, as evidenced by parasite current (reflector) only around 36% that of the driven element. Gain and F/B performance was, not surprisingly, poor. There was little benefit found by varying the separation distance; I tried values from 10 to 100 cm. More drastic measures would be needed to increase coupling, such as in the overlapping radial case.

The adjacent elevation plot is typical of the performance. Gain is only about 1 db better than a single vertical! F/B was typically below 6 db. Like the connected radials array, gain peaked at 3.5 MHz and F/B peaked at 3.8 MHz.

However SWR performance mimicked that of the connected radials array, being almost indistinguishable and so not worth showing the curve again. I also declined to mark up the antenna diagram with radial currents as it was not worth my time for this unpromising antenna.

One interesting difference was ground loss: it modelled from -1 to -1.5 db worse than the connected radials array. That is undoubtedly where some of the missing gain went. My guess (I didn't look at it more closely) is that the additional loss is due to a third of the radials being about half the length of the others.


Of these experimental models the only one that shows promise is the one with connected radials. It has good power flow between elements, accomplished with a robust physical design. I expect that it can deliver the modelled performance when built.

To get improved F/B from this array it would be necessary to feed both elements and use a power splitter/phasing system to architect the required electrical parameters in each element, in part by "taming" the mutual coupling to do our bidding. That system could also be used for direction switching. Designs are readily available, with perhaps the most comprehensive treatment found in ON4UN's Low-band DXing book (5th edition), chapter 11.

My approach would be to either build a 4-square or build the 2-element end-fire array described here. In the latter case, going with simplicity and maximum reliability rather than the best F/B performance. A simple, low-cost directional receive antenna would complement the parasitic array. That is, if you have the land.

It is possible to use elevated verticals to reduce ground loss and deal with any local topography and obstacles that impede the view of the horizon. While more challenging on 80 meters it is not necessary to raise the base 20 meters (λ/4) to get the benefits. Half that height can be effective, though probably no lower. There are ample resources on elevated radials, of which I'll point to two available on the internet: by VE2CV and another by N6LF. ON4UN's book also has many ideas in this regard.

But if you do so the antenna must be carefully modelled so that it can deliver the desired performance. You cannot simply lift the arrays discussed in the article and expect that they'll work.

Thursday, March 12, 2015

13 db

In this past weekend's ARRL DX SSB contest I did something I have not done since returning to the air over two years ago: I entered a contest using more power than QRP. For the first time I put my recently-acquired FT-1000MP to work in a contest. Running 100 watts is 13 decibels more than the maximum 5 watts allowed to qualify for the QRP category. This is a brief recounting of how it played out.

I entered 15 meters single band since my time was limited and I expected to be competitive by focussing that time on one band. Based on conditions before the contest I chose 15. My choice turned out well. While the band was not open right through the night it performed well up to 3 hours past local sunset, and came up again with the sunrise. The solar flare on Saturday had little impact on me; it had more effect on those further west aiming at Europe and Japan through the auroral zone, and of course those in Scandinavia. I'm far enough east to have consistently good openings to Europe. That makes all the difference.


Unlike with QRP it is possible to make most QSOs by running with 100 watts. True, it is nowhere near as impressive as what a kilowatt and big antennas will accomplish, but still a very effective way to run up the score. It helps that in Canada we can operate SSB below 21.200 MHz, away from the wall of US super-stations. You could hear me and other Canadians lined up from 21.2 downward running Europe for hours on end. Some US stations called me down there, which I could not work both for being out-of-band and worth no points.

This strategy does not work for other areas of the world, even where they can operate SSB lower in the band. But other than Japan the possibilities of runs of stations outside Europe are slim. I did some limited running of JA in the early evenings, and I'd have done more if not for a new local QRN source that peaks to the northwest.

Another advantage of running is multipliers. While working Europe I had a number of callers from Africa, the Middle East and Central Asia. These are multipliers I otherwise never heard. I ended up with 97 countries, just shy of a weekend DXCC on 15 meters. About 10 of those are uniques that I would not have worked but for running. That's what 13 db buys you.


With just the one small yagi I am at a disadvantage when trying to work stations off the side or back. It costs time to rotate the yagi to work one or two Caribbean or South American stations when the bulk of QSOs are towards Europe.

As in previous contests I have some diversity in the form of an inverted vee hanging off my house-bracketed tower. The 40 meters element of the cage inverted vee has a somewhat complex azimuth pattern on its 3rd harmonic but does effectively fill the holes in the yagi's pattern. The strategy is to switch to the inverted vee to work those odds and ends that are not always worth rotating the yagi.

With QRP this often did not work out, and I had to rotate the yagi if I wanted the points. Add 13 db and I could make the needed QSOs on the inverted vee. In fact I could often work them when they were directly off the back of the yagi since the F/B is not very high. As I've stated before, this is reason to question the need for high F/B for contests. A notable exception is stations with multiple yagis per band which do benefit from high F/B, since unlike single-yagi stations they can simultaneously achieve diversity and QRM rejection.


Concentrating on one band means that you will at times exhaust the pool of available stations to work. If you have a kilowatt and a big antenna you can keep running, seemingly without end when the band is open to Europe by attracting (and hearing!) more of the majority who have small stations. That doesn't work for me, even with 100 watts.

For a all-band effort, as I always have done with QRP, it is best to make frequent band changes. This allows time for a rotation of stations to occur. When, for example, you return to 15 meters there will be a number of new stations to work. Even when the strategy is to run this focus on rotation can work well.

Rotation works since most stations are either single-operator or casual participants, and they can only be on one band at a time. Although this is increasingly less true with the emergence of SO2R entrants (single-operator, two radios), it is not enough to make much a noticable difference. By spending time away from a particular band, or even from the shack entirely, a different bunch of single-ops will fill the band as they QSY from band to band. The available pool of casual operators who will answer your CQ also rotates. You will benefit from this rotation whether you S & P or run.

In my case -- single band and intermittent operation -- my frequent breaks made rotation work for me. If I'd operated full time my rate would have suffered unless I were to operate all  bands. An extra 13 db can do wonders, but not perform miracles.

Working QRP stations

My small antenna and 100 watts was enough to attract quite a few QRP stations while I was running. They are easy to identify in the ARRL DX contests since, for non-VE/W stations, power is part of the exchange.

Some of the 5-watters from Europe, even far-eastern Europe, had good signals that were copyable through the QRM and QRN. Some were a struggle to pull through, but then so were many 100-watt signals. So while SSB QRP is a challenge it should not be dismissed as not worth the effort involved. Being on the other end I was only too happy to pull them through and earn the points. Hearing them also made me smile since I know what it's like to be in their shoes.

It also pays to listen closely to the weak ones as you S & P across the bands. I worked one multiplier this way, a VP5, who was running 5 watts. He was CQing to little effect. I heard no other VP5 that weekend, so it's a good thing I was paying attention to every weak signal I ran across.

On an amusing note someone mused on the N1MM Logger group after the contest about how to log the station who gave his power as 500 milliwatts. Apart from the logging challenge it goes to show just how far QRP (or QRPp) can go, even on SSB. The lowest power station I logged was running 3 watts.

The exclamation point

Later Sunday evening while exporting my contest log and reporting my results I tuned around 20 meters. I ran across the fierce North American pile-up on E30FB, Eritrea. Of course I jumped in. I was still running 100 watts. Mix pile-up tactics and a heaping load of good luck and I got through in only 5 minutes. That was the exclamation point on my +13 db contest effort.

Next up

I have no immediate contesting plan except, perhaps, CQ WPX SSB later this month. So after 3 straight posts about contesting I am likely to return to antennas in my next article.

I know from web site statistics that antenna articles are by far the most popular, especially those that are about a particular antenna and not on theory or other general aspects of the topic. Since antenna articles take some time I can't produce them at the rate of one per week. So you will keep on seeing many articles that are about other topics that interest me, such as the one you are now reading.

I intend to cover some more general points about vertical antennas that I touched one previously. This will set the ground work for specific antenna designs.

Monday, March 2, 2015

CW Skimmers: The QRP Contester's Friend

Having been a QRP contester for almost 2 years now I have concluded that this is a really good time in the hobby's history to be doing this. The reason is technology. We often tend to think of recent technological progress assisting the more serious big-gun contesters (networked logging, global spotting, remotes, antenna design, etc.). Of course the technology also helps average and even smaller stations. What I want to argue here is that QRP contesting may be getting a better-than-average return on modern technology.

The technology I want to look at is not stuff like transceivers and station software since both big and little guns often use the same stuff. It's networking where I believe the benefit lies.

First we need to understand just how challenging QRP can be in a contest environment. My antennas are typical of suburban hams -- tri-bander & wires -- so we're equal in that. But when I run 5 watts I am -13 db weaker than the more typical 100 watts (barefoot) station. This grows up to -23 to -25 db below full legal limit stations. That's a lot when you consider, as hams, we'll endlessly argue about or waver on spending money over 0.5 db of transmission line loss or 1 db more yagi gain.

Listen to me

Let me give you a concrete example of how weak my QRP signal sounds at the other end of the QSO. 3V8SS in Tunisia recorded all his contacts in the recent ARRL DX CW contest. I placed well among the claimed scores in the QRP category of that contest. Go to 3V8SS's contest page and click on the link (upper left) to bring up a search box where you can enter my call (VE3VN) or any other call. Then select the found QSO (by band) to listen to 1 minute of streaming audio containing the selected QSO.

When you finish listening (and stop laughing) you'll understand what I'm up against. When calling other stations I am usually unable to get through when someone else simultaneously calls the other station. Even then I frequently need to repeat my call or exchange. Calling CQ is a particular challenge since on a busy band my signal is an easy one to overlook, and that's on CW with narrow bandwidth filters.

This is where technology comes to the rescue.


Spotting only helps if you're sitting on a frequency and calling CQ (running). Someone who hears or works you spots your call and frequency via one of the hundreds of gateways to the global spotting network. Other see the spot and, if they haven't yet worked you, QSY to your frequency and call. Both general logging and contest software make this as simple as a single click. The software may even highlight whether the station is needed and a new multiplier.

I was only spotted once during the contest, which is a little disappointing. Yet I was still quickly besieged with callers many of the times I started calling CQ on a new frequency. This brings us to another bit of technology that brought callers to my frequency.

CW skimmers and the Reverse Beacon Network (RBN)

Spotting networks only work if someone somewhere makes a conscious decision to spot you (note: never self-spot, and it can even get you disqualified from a contest). CW skimmers take that element of uncertainty out of the picture. There are a many stations around the globe running CW Skimmer by VE3NEA, or similar software, on a spare receiver. They may or may not be located at stations active in the contest.

Unlike spotting networks skimmers automatically scan the bands and report on activity. Primarily this is stations calling CQ or otherwise holding a frequency and inviting callers. While a standalone skimmer node has some value to its operator it becomes far more powerful when combined with other skimmers. This is where the RBN comes in.

Since the linked sites on CW Skimmer and RBN describe these technologies in detail I will skip their descriptions here and jump directly to showing why skimming and RBN are so useful to the QRP contester.

Let's do this with an example. The adjacent picture is an image of the RBN search on my call in the final hours of the ARRL DX CW contest last weekend.

As you can see I am getting a multitude of reports of my running attempts, often many every minute. It should be obvious that this is far more productive than relying on other hams to spot me. Most are not motivated to do so in my case since VE3 is hardly an attractive catch for anyone. Besides, most human operators will pay little attention to a signal as weak as mine. Not so the software.

You can see where I spent the final 2 minutes of the contest by calling CQ on 40 meters. It was a way to spend the time since I knew I had little chance of finding someone new in the time remaining. I was quickly answered by 9A8M, which turned out to be my final QSO of the contest. As I ran down the clock the skimmer spots just kept coming on RBN.

Notice the posting of the SNR (signal-to-noise ratio) on each spot. As with the 3V8SS recording referenced earlier you get an idea of how weak I am at many stations. I have few skimmer spots on 40 from the west coast or Europe. That absence of spots most likely indicates that I was below the noise or covered by QRM. This is useful feedback. On 20 and higher bands I fared better with my CQs, as you can glean from the earlier RBN spots.

Call CQ

Even if you're running QRP or small antennas you must spend time calling CQ in a contest if you are to build up your score. Many little guns or casual participants only call other stations, so if you never call CQ you won't work them. That costs you points. In the ARRL DX CW I made a point of calling CQ as often as possible in the final 12 hours of the contest since by then even the big guns are prowling the bands searching for contacts.

With a small number of human-operator spots the existence of skimmers and the RBN is a boon to little guns. Although many S & P operators may pass you by because you are so weak the multi-operator stations and those entering in "assisted" categories will pay you a visit when you appear on RBN. Thus you get a bigger boost from RBN than the big guns, who are stronger and more often spotted or called by the S & P crowd.

So call CQ and let the technology out there help to boost your contest score. Well, at least in CW contests. SSB skimmers will take a little longer to come along.