Side Mounting Yagis

My recent design of a side mounted yagi for 15 meters raises the question of how to do it. There are numerous techniques for accomplishes the feat, each with its pros and cons. My objective is to have the yagis stacked and rotatable. Mounting fixed yagis is relatively straight-forward, and not too interesting a subject for discussion. If I were to choose a fixed direction it would be towards Europe, which is the high-productivity path for contests from this part of the world.

In this article I present my preliminary survey into what's available, advantages and disadvantages, and setting of criteria to make a final decision. I have little experience with side mounting so there is the possibility of an error or two creeping in. Hopefully my calculations and research kept that from happening.

The esoteric: Ring rotators and rotatable towers

Neither of these options is in my plans due to expense and disadvantages with respect to my situation. I may have only one tall tower -- though I aim for two, eventually -- which has implications for contest operation.

A rotatable tower is especially expensive and would require substantial custom mechanical work to adapt my tower-in-waiting (LR20) to commercial products. But with one ground-mounted rotator (e.g. large prop pitch motor) you can turn all yagis on the tower. For daily operation this can be a perfect solution, but not in contests.

In a contest you want antenna diversity, whereby antennas can be simultaneously pointed in two or more directions. You can do this in contests if you have multiple towers, but I will be more limited. I plan to build a small contest station, not a super-station.

Ring rotators, such as those by Prosistel and AlfaSpid, allow full, independent rotation of each side-mounted yagi. But, again, they are expensive and require custom fitting to LR20. They have the advantages of full rotation (360° or more) and support large arrays. In most situations one ring rotator is required for each rotatable side-mounted yagi.

Another, less obvious problem is working on a tower with ring rotators. Safely climbing past one of these obstructions can be awkward, and unsafe if not done properly.

Simple side-mount

In the simplest arrangement two brackets are extended out from a tower vertex as platforms for a rotator and mast bearing. The yagi is mounted to the mast. For a trussed boom or stacked yagis the mast can extend further, with additional bearings as required. The rotator and its bracket typically take the full weight of the mast and antenna. The green circle represents an end view of the yagi boom and its mounting position on the mast.

Although bending moment on the rotator is not large you should consider a bearing directly above the rotator. It depends on the loads due to ice and wind falling within the bending load capacity of the rotator. The plates and tower brackets must withstand the dead and live loads. Here is a commercial example of brackets from IIX Equipment. They can also be home brewed by any ham with suitable metalworking tools.

Some choose a thrust bearing for the bottom plate and place the rotator inside the tower. The rotator turns the mast with a chain drive. Whether this is truly necessary is debatable since the rotator still requires above and below the chain to eliminate lateral loading of the rotator.

So we are done. Or are we? Have we truly achieved our objective so easily? Unfortunately, no.

This simple side mount is too simple. As designed it is not able to achieve 300° of rotation (360° - 60° for the projected angle of a triangular tower). In fact, it doesn't come close. Have a look at the top-down view to see what is going on.

The points where the yagi's boom strikes the tower (red lines) mark the limits of the rotation. This angle is approximately 120°, which is only ⅓ of the compass. Grey marks the azimuth angles the yagi cannot point.

Further, the direction a tower vertex points (there are 3 choices) must be the centre of rotation. The yagi can rotate 60° to either side. If the tower is already standing it may be impossible to select the best 120° range for your specific interests. In my case I want Europe (40° to 60°) within the range. I would then choose either to cover up to East Asia (330°) or Caribbean and South America (150° to 180°). I can't have both. A tower vertex must point approximately 30° or 100°, respectively.

So you would think this method of side mounting is a poor one. Yes and no. For some it may suffice. For others, like me, it is a useful first step. The reason is that it can be supplemented with a swing arm that will give 300° rotation. That's the next subject.

Swing arm

The typical swing arm is a rectangular or triangular attachment to the rotating mast. The yagi attaches to the pipe or plate at the outside edge. The length of the swing arm should just exceed the distance from the mast to the far edge of the tower. LR20, which has 20" faces, requires a swing arm of about 30", assuming a tower vertex to mast distance of 6" to 8".

By swinging the yagi around the tower in this fashion allows the desired 300° of rotation, as shown in the lower diagram.

Most hams build their own swing arms to their own specifications. There are commercial products available, such as that seen at the IIX Engineering link provided earlier. The swing arm must be very rigid and strong in the vertical and horizontal planes to survive high wind and ice loads, and protect the antenna, rotator and tower. The longer the swing arm and the larger the antenna the greater the engineering challenge.

With a swing arm there is some flexibility in choosing the yagi's centre position, something which isn't possible in the previous case. This is helpful if the tower is already built and a vertex is not pointing in a suitable direction. You can see this if you imagine the swing arm at the end of its rotation, up against a tower face. The yagi's boom has up to 60° of additional arc in which it can be oriented. Since this works on both ends of rotation the latitude of boom to swing arm orientation is ±60°. There are no unreachable compass points.

The approach is to first select the vertex that points away from the 60° area that is of lowest utility. In my case that area is between about 90° and 150°, which is mostly the south Atlantic Ocean and long path to the north Pacific Ocean. I therefore want a tower vertex pointing approximately 300°. Second, we must orient the yagi to adjust for the actual orientation of the tower. If the vertex points, say, 275°, the yagi should be turned 25° clockwise on the swing arm mast. That's it.

To close off, I'll point you to a couple of photo galleries of swing arms. First up is K5YA. Notice the rotation offset of the yagis on the swing arms, stacking and eschewing of a bearing to protect the rotator. Many rotators can handle the load, or may require more frequent service. Next up is K7EM. Here we see mast extensions for boom trusses and cohabitation with a yagi on a ring rotator. If you look around on the internet you can find many more examples. You may find a novel approach that strikes your fancy.

Rotator control

Standard controller for rotators typically do not support custom stops. That's a problem with side-mounted yagis. We want the controller to limit rotation before the boom or swing arm strikes the tower. It is preferable to use a controller that permits software-defined stops. Failing this I recommend using a low torque rotator such as a Ham IV (800 inch-pounds) and a spring or similar soft stop on the tower where the boom would otherwise strike.

Also take into consideration the mechanical stops of the selected rotator. Those stops ought to fall within the gray zones shown above, otherwise the rotator will prevent selection of all available direction.

Overall, I consider it almost mandatory to use a software-controlled rotator that can be calibrated to the specific needs of side-mounted yagis, including stops. Mechanical soft stops on the tower can also be used as a form of insurance in case of programming error or the yagi twisting on the mast in a wind storm at night. You can't always be looking out the window to see what's happening.

Electrical considerations

Symmetry is our friend when it comes to managing interactions. When we disturb symmetry we must carefully analyze the situation to assure no interactions disturb the performance of our antenna. Side mounted yagis, with or without a swing arm, are not symmetric with respect to the tower. Hence the concern.

To begin, in EZNEC I added a long wire running through the 5-element 15 meters yagi I propose to side mount and stack. This wire is 18" in diameter, which is approximately equivalent to a 20" face triangular lattice tower. The objective is to test for interactions between yagi and tower as the yagi is rotated around the tower.

The tower model is truncated and made resonant on 15 meters. There is no easy way to fully model the tower, or to arrive at results that are at once both specific and general. Instead I chose to pursue a worst case result by centering the tower segment with respect to the boom and making it long enough and resonant to excite interaction modes.

To this end I adjusted the tower "wire" to resonate ~40 meters, with the third harmonic at 21.2 MHz. That is, it's a 3λ/2 vertical dipole. The model is placed in free space to isolate the interactions from other environmental factors, including guy wires, ground and other antennas. If I can reduce interactions in this model there should be none of this type in the real world. Of course other interactions must also be addressed, but those can be done separately. In antenna models, as in other types of problem solving, it is best to vary one variable at a time.

In this antenna the mid-point of the 380" boom is 190". The positions of the first and second directors are 106.5" and 239", respectively. The second director is 49" from tower centre, but can come as close as 39" when parallel to a tower face. Clearly the design and construction of the yagi enters into the equation. However in this instance I will only focus on this particular antenna, not yagis in general. I need to keep this work focussed so that I don't get too far afield at this time.

With the model built I proceeded to "move" the position of the tower to different points and measure the resulting impedance and far-field pattern changes. These moves were in the X direction (parallel to the boom) and in the Y direction (parallel to the elements), but always staying within the space bracketed by directors 2 and 3. Without being exhaustive or comprehensive I was able to discern a few general trends that I found helpful.

Note that in the referenced diagrams above I truncated the yagi elements (green) to fit the illustration. In reality directors 2 and 3 or the 5-element 15 meter yagi are ~134", which is several times longer than drawn. The swing arm is also not quite to scale.

• When the tower is adjacent to the boom there is negligible interaction, even where the tower gets as close as 6" to one of the directors. This is good news, and ameliorates that particular concern. It also tells me that fixed side-mounted yagis are not in general compromised when one or two elements get close to the tower. This is increasingly concerning at higher frequency bands where yagi elements are closer together and the tower is larger (wider) as expressed in wavelengths. Interaction could become significant on higher bands, but I did not test this.
• The further the boom is from the tower (that is, in the Y direction, parallel to the elements) the greater the distance required from the adjacent elements to manage interactions. For example, when the separation is 24" (60 cm) the tower should be a minimum of 9", and preferably 12", from the directors of this 15 meter yagi. At double this distance (48" or 120 cm) the elements should be kept a minimum of 18" from the tower, and preferably 24". This is unsurprising since (capacitive) coupling becomes more pronounced toward the element tips; this is the same mechanism used in a Moxon rectangle and also confounds the tuning of fan dipoles.
• Tower resonance by itself has a negligible impact on yagi performance. However when there is interaction as described in the previous point the presence of a resonance exacerbates the problem.
• It takes a severe interaction to reduce gain by greater than 1 db. When this occurs the main lobe and rear side lobes become asymmetrical. SWR also increases due to the shift in impedance. From the model it appears that impedance deviations are a strong indicator of interaction; that is, you'll see the SWR increase, especially high in the band, before pattern distortion becomes significant.

As I said above, these cannot be taken as general rules. With different towers and yagis the situation will differ, at least in its details. NEC2 can also give misleading results for closely spaced wires. Even if interactions are discovered at some points along the rotation arc of side-mounted yagis that may be acceptable if not severe. Perfection is impossible.

If you play with a pen and paper you'll notice that the worst case for tower interaction is with the swing arm since it places the tower further in Y direction with respect to the yagi. Any rotation from the orientation show in the diagram above brings the tower closer to the boom and therefore will tend to reduce any interaction. Except, perhaps, when at the ±60° points where a direction will most closely approach one of the other two tower vertices. Keep that in mind when designing the yagi and side mount.

Next steps

The girts on the LR20 tower are every 5' (two per 10' section) and are ideal for attachment of hardware to support side mount yagis. I took measurements of the bolt holes on the girts to get an idea of how to proceed. It is also possible to use commercial clamps that attach to triangular tower legs (e.g. Trylon). However my current plan is to build my own supports.

Out of prudence I will undertake some rough calculations of the loads the yagis will impose on a swing arm, rotator, bearings and mast under wind and ice loads. The tower appears up to the challenge (from talking to other LR20 owners) but that still leaves all the side mount hardware. Because of the array's size and weight I may opt for a bottom thrust bearing so that the rotator can be serviced more easily.

Since the stacking height on 15 meters is quite large there will need to be a bearing mid way. An alternative is to use two independent rotator and swing arm assemblies, but I prefer to turn the antennas as a single unit.

To minimize interaction with the tower I may shift the yagi mount off centre. Weight and wind load compensation may be needed to avoid added mechanical stress. The boom truss will help to avoid boom oscillations due to any remaining imbalance.

Depending on time I may first fix the antennas towards Europe, then build the simple mast system, and only later add swing arms.

Personalization and the Multi-op Contester

In our own stations we all have a tendency to arrange and configure equipment as we like. There is no one else to please but ourselves. Put the display above or beside the transceiver? Do what you like. Set the keyer to iambic A or B? Do what you like. Selection and position of windows for your favourite logging program? Do what you like.

All this customization flies out the window the moment another ham sits down to operate. Their station ideal is very likely different from yours. There is the possibility of endless argument over which arrangement is better -- there are quantifiable differences -- but in the end it almost always comes down to personal preference. Arguments over what's right and what's wrong go nowhere, and stress friendships.

This approach of agreeing to disagree becomes difficult in a multi-op contest. There is one station and two or more opinions of how to set things up. I was strongly reminded of this truth when this past weekend in the CQ160 CW contest when I operated as part of a multi-op (VE2OJ) for the first time in 25 years. I like to pride myself on my flexibility, my ability to accommodate other station setups.

Accommodate is what I did since I was the newest team member. Yet there was lingering discomfort because I've become a little rigid, like most hams. I got by just fine other than a few small things that I could quickly adjust when I sat down to operate. Others could change these back just as easily, which they sometimes did. But I did leave a few things the way others like since that is a great way to experiment.

In this article I'll discuss some of the differences I found and explore arguments in favour of one arrangement versus another.

Centre of attention: rig versus screen

A common approach is to put the rig front and centre at the operating position. In modern contest stations with fully integrated rigs and computers this should be reconsidered. The best operators have already decided, and pushed the rig off to the side. Sometimes almost completely out of sight. It is a question I first pondered in this blog soon after my return to contesting. Later I discussed how I changed the arrangement for the better.

The difference is a simple one yet profound in its effects. In contests you are either running or hunting. When running the radio has little utility. Filters and RIT to tune in callers are accessible from the keyboard. Call sign and exchange entry involve only the screen and keyboard. When hunting, with assistance, the screen shows the spots and needed multipliers, which you (typically) click on with a mouse to QSY. All sending is by keyboard, microphone or paddles.

Only when hunting stations unassisted is the rig of more direct interest. In particular the VFO knob. Operating QRP I do more hunting than running than higher power participants. Even so I find that it is better to place to rig off to the side. It was easy to train myself to operate the rig with my left hand, type with both hands and send CW with the right hand. Give it a try. I'll think you'll like it.

With the rig up front your hands and clothing may brush the keyboard when reaching for and using rig controls. When the screen is above the rig the eyes can tire from constantly jumping up and down; in ergonomically designed computer desks (for general use) the screen is low, not high. Touch typists like myself can escape some of the effort of having to look up to a high screen, but not nearly enough.

Above is my current experiment with going SO2R QRP (the KX3 is only posing since it isn't connected to anything). The laptop screen is small for two entry windows, which I will eventually deal with. Some reaching around the mouse and paddles is required to reach the second radio. Since the operating table will remain as is for the time being I will have to be creative. However the screen and keyboard will remain at the centre.

Sinister effects

I am in the majority in that I am right handed. A mix of left and right handed operators in a multi-op can be awkward in a CW contest. The problem is the location of the paddles. Either have two sets of paddles or configure the operating position to allow rapid paddle placement during operator shift changes. Our left-handed operator made do with the paddles on the right, but that is unfair to him.

Operator profiles

N1MM Logger supports operator profiles. When you sit down you type Ctrl+O and enter your call. The QSOs you make are tagged with your identity, and can be used to configure the software to your personality. This may include small things such as screens and screen positions, and important ones such as messages in your own voice (SSB contests).

We experimented with profiles during the contest. This is something worth setting up before the contest: each operator sits down, makes desired adjustments and saves the profile. It may seem unimportant to customize the operating position this way, but it can make a difference over the course of 24 or 48 hours. For example, do you use iambic A or B keying? That was a popular item to switch when sitting down for one's shift. How about CW and CW-R (reverse)? Again, it's a small thing that can affect operator efficiency.

Logging software

We used N1MM Logger+ integrated with the WinKeyer and K3 transceiver. This is the same as my own station, other than the rig (mine came along as backup). This difference is mostly immaterial since N1MM abstracts rig functions so that they function the same for all rigs, provided the rig supports the function. This is valuable in a multi-op where each operator may have a different rig in their own station. It's the logging software (and other contest-related software) that is key, and everyone's familiarity with it.

In run mode some liked to tune stations by rig control, others by keyboard RIT and others by filter width and shift. N1MM is compatible with all of them. It is only important to reset or check settings when switching operators.

We had ESM enabled (enter sends message), though not everyone used it, or used it for only select situations. Happily N1MM mostly acts sensibly when function keys are used when ESM is enabled. Mistakes were made but were usually easy to correct during the (many) quiet times. The software can't read minds and so may not do what one expects. I use ESM almost exclusively in my home station, only reaching for the paddles and function keys to say hello to a friend or to struggle through a difficult QSO.

Receiving antenna

Serious low band operation benefits from one or more directional receive-only antennas. These may be magnetic loops, beverages, phased verticals, among other options. We had a beverage (BOG) towards Europe. It is necessary to select the antenna to receive on, as often as every QSO.

I hadn't given the problem much thought since I do not have a receive-only antenna at home. There are two distinct approaches: manually switch the receiver between the transmit antenna and the receive antenna; or, diversity reception, with one antenna for each receiver in the K3 (or similarly-featured rig). We used diversity with a balance control to adjust how much of each was fed to the headphones. Alternatively each receiver could be fed to each earpiece of stereo headphones.

I have not made up my mind which approach I prefer.

Be flexible

Running a team by consensus sounds nice in theory. Except that getting to consensus on every issue is time-consuming and often fails anyway. Recognize that personalization of the operating position cannot suit everyone all the time. Although I had an opinion on most everything I was always ready to modulate my expectations. This was a fun, social weekend, and that was paramount, not the final score.

Would I have arranged the operating position differently? Yes. This should be apparent from what I've written in this article. I could claim that with my contesting ability and experience that my views ought to be suitably weighted in the discussion. However that is not right since all team members should be equal.

It is better to use one's skills to make the best of the situation as presented. Arranging the station to my vision of what works best is not necessarily the best for others, and I am just one operator among many.

Indeed, flexibility should be in every contester's toolkit. Look upon inefficiencies as a challenge, the same as a geomagnetic storm or other external events. Being inflexible leads to conflict and animosity, not a better score.

5 Elements on 15 with a Found Boom

I find myself with two 32' (10 meter) booms that are begging to be put to work. These booms are 3" OD but the walls are only 0.058" (~1/16"). While I could lengthen them with a suitable centre section of pipe that wall thickness dictates that bands below 15 meters must be excluded from consideration. Since 10 meters will be of limited utility through the coming solar minimum I therefore settled on 15 meters. So I set out to design or adapt a design for 15 meters.

The chosen design may be too specific to my own needs to be of great interest to others. Since the process of getting there can be employed by others writing about it can be useful. I'll step through my process of selecting a suitable design and how I modified it to meet my objectives.

This is purely a design task, but one that I'm taking seriously. I will go through the steps of selecting a taper schedule and employing EZNEC's SDC (stepped diameter correction). The Leeson correction works well and should lead to zero fuss construction and tuning. Hopefully construction will be in the not too distant future.

Setting objectives

For contests the antenna must be low SWR across the entire band -- 21.000 to 21.450 MHz -- have reasonable F/B and as much gain as allowed by the other constraints. Since boom length is one of the two primary determinants of maximum theoretical yagi gain, the 32' boom limits the gain to no better than 11 dbi on 15 meters. In any case the stacking gain (~3 db) is greater than going with an exceptionally large, long boom yagi (~1 to 1.5 db). I can afford to focus on better F/B and match than squeezing out every 0.1 db of additional gain.

This antenna is intended for the 45 meter tall tower I hope to raise later this year. I plan to stack them on that tower, initially fixed then rotatable. The most likely stacking arrangement will have the upper yagi at ~35 meters and the lower one at ~25 meters. They should play well towards Europe and other paths. The heights are chosen to avoid interaction with a 40 meter yagi at the top of the tower and to avoid guy wires. The stacking distance is about 0.7λ, which is near ideal for yagis with a boom length of 0.67λ.

Designing 2 and 3 element yagis is straight-forward. The search space of element lengths and spacing is easily explored. As each additional element is added the challenge to discover an optimum design rapidly increases. Even for just 5 elements the optimization search space is already very large.

Lucky for us that yagi optimization has been going on for decades. Look around and you are sure to find a ready-made design to suit your needs. You should only take care to understand what the word "optimum" means in every instance, since for some this is about gain, F/B, wide-band match, cost or wind load, or some combination of these or other parameters. If the objectives for a design are not stated you ought to be suspicious.

I will therefore begin my search with a "stock" design.

Finding a design template

There have been several generations of designs for optimized yagis. This may seem odd since physics has not evolved. It is modelling software and field measurements that have improved. For yagis we can begin with the NBS (National Bureau of Standards, in the US). For hams the next big step is found in W2PV's seminal work from the early 1980s (see the out of print book "Yagi Antenna Design"). We can do even better today. Two that are of greatest interest to me are those in the ARRL Antenna Book and WA3FET's OWA (optimum wide-band array). There are more if you want to investigate further.

Since W2PV elaborated and improved upon the NBS designs we can start there. From his (pre-NEC) software modelling and optimization he found that making the design complicated yielded only small improvements. He therefore standardized on equal element spacing and equal length directors. This limits the variables to boom length and tuning of the parasites. Unfortunately he didn't have much to say about 5-element designs -- he jumped from 4 to 6 elements -- even though that is ideal for a boom of this length. You cannot simply take a 6-element design and lop off the last director! He also did not say a great deal about match bandwidth, and that matters to me and, I think, most hams.

Modern modelling software made it easier to search the vast space of combinations of element length, placement and boom length to do better. Even so the W2PV designs compare favourably. Even so I opted for a modern design. I did so using the ARRL Antenna Book (22nd edition). Nowhere in there will you find a 5-element 15 meter yagi on a 32' boom. Yet this can be an excellent boom length for such a yagi.

Recall that a yagi's gain is primarily determined by boom length, only requiring enough elements to ensure sufficient mutual coupling to make effective use of the boom length. We then vary element lengths and spacing to get the best combination of gain, F/B and SWR for our needs. A 32' boom on 15 meters is ~0.67λ. Gain better than 10 dbi (free space) is achievable, along with good F/B.

By noting that 32' on 15 meters is the same fraction of λ as 48' on 20 meters I chose the 5-element 20 meter yagi on a 48' boom as my first template. This design shows excellent gain, F/B and broadband match across the 20 meter band. It is an easy matter to scale the design to 15 meters. Parasite tuning is ±6.6% for the reflector and director 3, with the other two directors tapering in length toward the centre frequency.

Adapting the design to the boom

I scaled the element lengths and spacing by multiplying by ⅔ (14 MHz divided by 21 MHz) and adjusting fractionally to squeeze down a further 6" by moving director 3 inward. I used the element taper schedule in the ARRL Antenna Book for a heavy duty 15 meter element.

In the model I built one element for the taper schedule and selected a segment length of 6". The segment length for the element tip will vary somewhat from that value. The centre "tube" for the element-to-boom clamp is one wire of one segment spanning the centre of the element and joining the element halves. I then copied the element for the other four elements and adjusted all element tips to the calculated (scaled) lengths.

It is unsurprising that scaling is insufficient since element diameter and taper affect resonance. By inspecting the modelled gain, F/B and impedance I determined that the performance I want at the 21 MHz frequency is found at 20.6 MHz. All the elements were therefore scaled by 20.6/21.0 by shortening the tip lengths. When scaling antennas always multiply and divide by a scale factor; never add or subtract a fixed amount.

Half element taper schedule:

• 3" length of 3" diameter, to account for the 3" x 6" element-to-boom clamp
• 27" length of ⅞" tubing, half of a continuous 54" length for the centre section of the full element
• 36" length of ¾" tubing, which is half of the visible portion of a continuous 112" length that is inserted through the ⅞" tube
• ½" tubing for the element tip, adjusted to the required element length, not including the portion hidden within the ¾" tube

The driven element is cut in the centre and insulated from the boom for dipole feed and hairpin termination. A ¾" fibreglass tube or rod spans the centre of the driven element for mechanical strength.

Element half-lengths and spacing from the rear of the yagi are as follows. The tip length is the half-element length minus 66" (the rest of the half-element) plus 3" for overlap.

• Reflector: 144.11"; 0"
• Driven element: 135.7"; 48"
• Director 1: 133.8"; 106.5"
• Director 2: 131.75"; 239"
• Director 3: 126.77; 378"

The scaled frequency range is 525 kHz on 15 meters, which exceeds the required 450 kHz. This allows latitude to optimize the SWR.

The hairpin is a shorted ~400 Ω stub 11.5" long, made from ½" tubing spaced 4" centre-to-centre. The stub should be several inches longer to allow for adjustment with a shorting bar. The feed point will out of reach when mounted on the tower, but that's a topic for another day.

With different stub parameters the length will change. The inductance of a short stub is proportional to the length and inversely proportional to the nominal impedance. This handy approximation only applies to transmission line lengths that are short relative to wavelength.

Performance

The antenna is remarkably consistent across the band. Unsurprisingly it behaves very much like the 5-element 20 meter yagi it is based on, the performance of which is shown above in the YW screen capture (YW is yagi design software included with the ARRL Antenna Book). A example of the azimuth pattern is shown at right.

The ARRL optimized design has parasite tuning of ±6.6%, measured for the reflector and director 3. The other directors fall in between, and the director spacing is quite wide. This is an antenna that will require wind load and weight compensation so that it is mechanically balanced.

Radiation resistance has a steep drop at the high end of the range where gain reaches a maximum. The antenna is tuned to ensure that this point occurs above 21.45 MHz. Doing so gives us the best conditions for a broadband match with a simple network. R and X components of the feed point impedance vary little across the band.

The completed yagi model has a forward gain that gradually rises from 10.2 dbi at 21 MHz to 10.45 dbi at 21.45 MHz. F/B stayed in a range between 22 and 26 db, which is excellent. F/B was measured at the maximum side (back) lobe rather than the exact rearward direction since the side lobes change position with frequency. I believe this gives the best idea of its QRM and QRN rejection potential.

Plots of gain and F/B appear further below, compared to a variation of the design. These performance figures agree well with the 20 meter yagi this antenna is based on (shown above in the YW screen capture).

The hairpin (beta) match was calculated at the end of the process, once the yagi was completely designed. As can be seen from the EZNEC plot below it does very well indeed without the contortions I went through with the 40 meter 3-element yagi I recently discussed.

The SWR is below 1.3 across the band, which is ideal for broadband transmitters and amplifiers. With a smidgen of transmission line loss the SWR in the shack will be even lower. There is no need for an OWA design and the added load and cost of a couple resonator. However we do want to use low loss coax to ensure that our design and construction effort is not wasted!

Optimizing further

It is tempting to push the design further to try and get closer to the theoretical maximum gain of ~11 dbi. We can't push too much or we'll lose the excellent broadband match and F/B. High gain is associated with high Q. It is also inadvisable to play around too much with element spacing and tuning since manual design of this nature is not conducive to getting good result. This antenna is already heavily optimized and very sensitive to small changes. I know, I tried!

We do have some room for adjustment since the match is so good; some increase in antenna Q will still result in an acceptable broadband match. To ease into this I tightened the parasite tuning from ±6.6% to ±5.5% by shortening the reflector to 143.38" and lengthening director 3 to 128.68". This includes shifting the entire yagi (adjusting all elements) down by ~100 kHz in order to centre its best performance within the band. Adjusted directors 1 and 2 are 134.47" and 133.07", respectively.

A further tightening of the tuning to ±5% degraded gain and F/B. Small changes to the lengths and spacing of the other directors degraded gain and F/B. I doubt we can do better even with serious optimization modelling.

The match requires a driven element length of 135.8" and a stub length of 9.8". The SWR is little changed, except for the beginning of a sharp increase at the high end of the band. It is still a very good 1.6.

Comparing the gain and F/B of the two yagis is instructive. While I was able to improve the gain as much as 0.2 db in the CW segment that advantage disappears for SSB, where both yagis are roughly equivalent. F/B is similar for CW and the lower SSB segment and then becomes as much as 4 db worse higher in the band. However the difference is quite small.

Choices, choices

In my opinion the differences do not clearly favour one design over the other, and both are excellent. The ±6.6% yagi is more consistent across the band and may be acceptable for that reason alone. Luckily I am in no rush to finalize my choice.

When I get to the point of building these antennas I will have more to say with regard to construction, tuning, installation and stacking. I am looking forward to building this antenna.

CW Switching with PTT

One of the features of the K1EL WinKeyer that I recently purchased is PTT transceiver keying. I enabled this feature for the first time in the NAQP contest two weekends ago. I did this via the N1MM Logger+ contest software, which only enabled the feature during contest operation. It all worked very well indeed, and enhanced my effectiveness in the contest. This feature is a keeper in my station.

If you are unfamiliar with the use of PTT for CW operation, and you like the advantages discussed below, read on. I'll begin with a review of what PTT (push-to-talk) means in the context of CW -- until fairly recently PTT has primarily been used for phone modes -- and how it compares to other transceiver switching techniques.

As a former boss of mine, a very successful entrepreneur, was often heard to say: "timing is everything." This is very true, whether we are talking of business, personal life or...CW. The advantage of PTT is all about timing, as we'll see.

Receive to transmit, and back again

There are several techniques for switching a transceiver between receive and transmit when using CW. These are:

• Break-in (QSK)
• Semi-break in (VOX equivalent)
• PTT

If you use full QSK you can probably skip the rest of the article since you already use the superior method! This assumes that your rig is capable of QSK and, if you use higher power, that the amplifier can tolerate rapid switching. QSK is a delight to use in DX pile-ups and contest exchanges since you always know what's going on and can instantly react. I love this feature of my Elecraft KX3 since it works so well. But that's QRP, for which solid state QSK is cheap and effective.

It is more typical that transmitters, especially where an amplifier is involved, are incapable of QSK, or it involves the annoying clacking of relays. For long years the switching method of choice has been semi-break in (VOX in older rigs), in which the transmitter turns on when the key is closed and returns to receive following a hang time after code transmission has ended. The hang time is set with a pot in older rigs and a menu item in newer ones.

Although semi-break in works well in typical daily operation there are disadvantages:

• You cannot hear what is going on while your are transmitting. During the excitement of DX chasing and contest you will often double with other station (both transmitting at the same time).
• On some rigs, and especially where an outboard amplifier is in use, the first code element may be truncated or missed entirely due to slow turnover between receive and transmit.
• Hang time may be tied to SSB VOX timing or must be set to a fixed duration, and is not scaled to code speed or responsive to operating conditions.

Setting up

I use a Y adapter on the PTT jack of my FT-950 so that both the WinKeyer and a foot switch can control PTT for CW and SSB, respectively. Until I put in the Y adapter I temporarily used VOX on SSB, which though not my preferred choice on phone the inconvenience was minor since I operate SSB less than CW. The RCA connector and a bit of software configuration is all that is needed to enable PTT. Well, that and disabling break-in with the push of a button on the rig's front panel. The rig's internal keyer must also be disabled when using an external keyer such as the WinKeyer.

Wired back panel of my WinKeyer; for SO2R the second rig has its own set of connectors

When properly configured key closure is detected by the keyer rather than the rig. The keyer closes the PTT line to the rig when the first code element is sent.

Alternatively, some operators use the PTT line for the amplifier and use semi-break in on the rig since the cascade of relays from time of key closure can truncate the first code element. I've heard it happen numerous times during CW contests where high speed is the norm. I don't need to deal with this problem right now since I do not have an amplifier.

You can set a parameter to delay the start of sending by a few milliseconds to ensure proper transmission of the first code element. This isn't necessary on my rig, and should not be on any rig. It is in any case an imperfect solution since the timing offset is unnatural at more than a small number of milliseconds. Set this delay to zero unless you suffer from a sequencing problem with a external amplifier, as described above, yet you still want the full benefit of PTT.

My current WinKeyer settings in N1MM Logger+

Take care that you do not inadvertently use PTT mode when break-in or semi-break in is enabled on the rig. It can result in some puzzling results. My FT-950 has a front panel control for break-in (QSK or semi, depending on menu setting), by which I can easily switch to PTT at the start of a contest.

Paddle operation and setup is a little more complicated with PTT. With memories and software-generated message the keyer knows precisely when the message starts and ends, but not so with a human operator. There are settings to get the timing of PTT switching to suit your needs.

Most important is the hang time. This is the delay from completion of a code element, with neither paddle closed, before switching the PTT back to receive. It is similar to the hang time (or VOX delay) for semi-break in. The WinKeyer uses a variable timer based on keying speed, which is better than a fixed hang time.

Advantages of PTT

I quickly appreciated PTT as I began operating in NAQP.  Good results are most evident when playing memories and software-generated messages. In contests, where everyone is quick on the trigger, you are almost assured of never missing a single dit of the other operator's message due to the hang time delay of semi-break in.

Of course it doesn't help if the other guy starts sending before you've finished, which does happen! Other than that situation you never again have to ask for repeats or wonder if he copied the first letter of your call as A or V: you'll hear those first dits even at 40 wpm.

When you do need to reach for the paddles to send a custom message, or simply to say hello to a friend during the contest, you'll appreciate the speed-responsive hang time discussed above. I recommend using this feature rather than alternatives since it works so well, no matter the speed at which you're sending.

Beyond contests

Several days after NAQP I decided to enable PTT full time. The advantages of PTT also apply to DXpedition pile-ups. Since I've been mixing it up with the horde calling K5P, VP8STI and others this past week it was a sensible step to take.

Now I miss very little of what the DX station is sending. By hearing more of what he's transmitting I more often copy the call sign (or fragment) of the station he's calling. I can therefore better identify the frequency of that station and adjust my transmit frequency accordingly.

I have also reduced the times that I have fruitlessly called when the DX has already responding to another station. This is often done by the sending of a call sign fragment at 35 wpm, which you can easily miss with semi-break in. PTT gets you in and out of the pile-up faster and more successfully. Although I cannot claim that PTT helped put K5P and VP8STI in my log this week I am certainly more effective in the pile-ups.

So even if you're not a contester there are reasons to make the switch to PTT. If your keyer doesn't have this feature this should prod you into upgrading. You may be surprised by how big a difference ~100 milliseconds can make to your operating. Of course you can go full QSK and do even better. But buying a new keyer is more economical than buying a new rig.

K5P: It Should Not Be Easy

There is a great deal of interest in the ongoing K5P DXpedition to Palmyra Atoll. In these first few days of the 2 week operation there is a pervasive din of complaint. They are too weak or they are only working the other guys. There is something wrong, but not with K5P. The problem is us.

Who ever said that working DX was meant to be easy? If it were easy what would be the value of DXCC and achieving DXCC Honor Roll? None, that's what.

Accomplishments easily achieved are the ones we least remember and cherish. Working K1N Navassa Island was not noteworthy for me since it is almost in my backyard and I used 100 watts. Well, except for perhaps 80 meters. Working FT5ZM Amsterdam Island with 10 watts, including 40 meters with an inverted vee, I can justifiably be proud of. It required a serious effort.

I, too, have yet to work K5P. That's okay. There is yet time for propagation and luck to perform their magic. Even if I fail to work them that is acceptable to me. It is one more country I can anticipate for the future, perhaps at least 10 years hence. I expect to work hard for it, not have it come easy.

In any important objective in ham radio, as in life, it is the pursuit rather than the catching that is the most fulfilling. For me, QRP with small antennas was like that: making contacts, working DX and winning contests. It added spice to my renewed interest in ham radio after being QRT for 20 years.

The funny thing is that working rare DX is easier today than ever before. One big driver is money: people around the world are more affluent than ever before. Towers are higher, antennas are bigger and rigs are better and more powerful. There is also the ease of travel and the wealth to mount DXpeditions to remote areas of the planet. Spotting networks relieve us from most of the tedious effort of finding the DX.

The sense of entitlement exhibited by some is disappointing. I do hope that those who endlessly complain about K5P learn to adjust their expectations and enjoy the chase. That the K5P operation is restricted to small antennas only enhances the challenge and excitement. Adding a counter to a DXCC total is not what it ought to be about. Consider it an incentive to improve one's skills and to build bigger, better antennas.

Spying on Antenna Farms

Let's have some fun to start off the new year. Have you ever tried looking at your or someone else's antennas on one of the mapping services? I have done so several times. It is surprising what you sometimes can, and cannot, see in those satellite images.

Since the viewing angle is usually quite steep towers, houses and other structures can appear strangely unfamiliar. Some, like Google, will give you a bird's eye view by massively processing the images. But for this exercise I'll stick with the "raw" images from Google Maps. Let's see what we can learn from those images. Are my antennas real? Are yours? We can find out.

Google Maps satellite image of VE3VN

The image at right is a cropped screen capture of my house and part of the lot from Google Maps, at maximum magnification, on January 5, 2016. However, that certainly is not the date of the satellite image. The watermark says 2014, which will be later than the true image date.

Although the resolution is barely adequate there is a great deal to see if you take some time to analyze the image. I'll walk through this so that you have more tools at your disposal for analyzing images of your own antenna farm, or others.

Antenna size

There is a correlation between true size of antennas and towers and what their owners claim. Most hams are honest reporters but there is a tendency to exaggerate as their size declines. The satellite images help us to verify the truth of those claims.

HF yagis are usually easy to see in these images. Only under ideal conditions will wire and VHF/UHF antennas be well enough seen to be evaluated.

At first I thought the adjacent image was of the boom on my Hy-Gain Explorer 14, with the elements washed out. A closer examination of the tower shadow and the image detail reveals that the image is older. That's the 30' Golden Nugget tower supporting my 4-band TH1vn (modified TH6 driven element), oriented broadside to Europe and the Pacific.

Some wires are visible. The sunlit portions of the ⅛" guy wires can be seen going north toward the house anchor and also southwest and southeast to their tree anchors. The inverted vee is not visible, although you can see the shadow of the house-bracketed 14 meter tall mast that supports it.

Tower height

This is a more difficult challenge. Restricting ourselves to linear measures on the image -- Google includes a scale on the image -- as our only data it is impossible to determine tower height. You must also know one or both of the satellite position and image date.

If you know the satellite position you can calculate the viewing angle. With that and the projected linear length of the tower the true height can be calculated with simple trigonometry.

If you know the date you can calculate the solar elevation from the time of day (shadow direction, like a sun dial). Measure the length of the tower's shadow (assuming level ground) and the height can, again, be calculated with simple geometry.

When Google constructs a bird's eye view they make use of the satellite position. You could try to figure out tower height from that construction. I haven't tried that. If you try it be aware that the images are distorted when processed in this way in order to provide a "sensible" result. Linear measures are often unreliable after image processing. Look closely and you'll see numerous instances of distortion in bird's eye view and Streetview.

Yet there are ways. These are somewhat in the manner of that old joke: how do you measure the height of a building with a barometer? For example, infer the tower type from the image or outside information. If the resolution is sufficient you only need to count off a few of the horizontal tower members on the tower's shadow and combine that with the dimension data from the spec sheet. Count them all or use the shadow length to calculate tower height.

Other height-measuring techniques using the satellite image are left as an exercise to the reader.

Dating the image

When was it taken? Can we find out? Often the answer is yes. I've left enough evidence of my antenna comings and goings on this blog that we can estimate the date. Although this is almost entirely useless for spying purposes it is interesting (to me at least) so let's proceed with this topic and see what a simple picture can tell us. At stations going through lots of changes you might even catch antenna work in progress, as we'll see.

First, we're facing north, so the sun is behind the satellite. Although there are many trees at the edges of my property, with branches often meeting in the middle (squirrels love it), everything of importance is sunlit. That is very helpful.

We can locate the satellite. Follow the shadow of the tower to its base. Compare the projected length of the tower to the shadow (~0.2), do a little trigonometry, and we see that the satellite is ~10° east of the zenith point. Image processing stretches these images so that the trapezoidal projection of a square patch of ground due to the oblique viewing angle can be stitched together with others to form a contiguous map. Some distortion can creep in, although it should be small in this image since the satellite is close to the zenith.

The TH1vn dipole was put up in early summer 2013 and taken down in early summer 2014. The image had to be from those 12 months -- the 2014 watermark is consistent with this. Notice that the dipole is sitting directly atop the tower. The extended mast for the 40 meter delta loop is not present. Since the delta loop went up in late October 2013 either the image was taken between July 2013 and early October 2013, or June 2014 as it was being disassembled. That the greenery is in full display confirms this.

The direction of the shadow tells us the image was taken shortly after 2 PM EDT. As for the time of year, well, the tower is 30' tall, the house is ~47' from the tower base and my latitude is 45.5° (grid FN25). Since the shadow is ~36' long the sun's elevation is ~40°. It's close enough to local noon that we can say the sun is slightly south of the celestial equator. Therefore it is most likely early fall of 2013.

Now I draw your attention to a small detail. Look at the upper roof. There is a faint arc running from the fireplace chimney on the left to the roof edge on the right. I quickly ascertained that it is a rope I had rigged as a safety line. The rope was arranged so that when clipped into my safety belt I could stand at the edge of the roof, and move right or left, without worrying about falling. This allowed me to safely work on the mast and inverted vee.

An blog article from September 2013 shows that I was putting up the first version of my multi-band inverted vee, including the mast. The bracketed pipe went up earlier in the summer and was first used to test a 20 meter delta loop. The shadow of the antenna mast is visible on the lower roof. There is no sign of the delta loop. This narrows the date range.

I left the safety rope on the roof for some time since I didn't want to redo it each day I was up there. Tuning the antenna and adjusting the mast supports dragged on for a while. It is therefore quite possible that it was a few weeks past the equinox, as initially estimated above. It is also possible that my measurement of the shadow or recollection of the distance between house and tower is inaccurate, or even that the aforementioned distortion is present in the image. So it could have been mid-September, right around the equinox.

Are you feeling yet like Sherlock Holmes?

Checking out the competition

Out of curiosity I checked out a couple of large stations located on rural acreages. I was to be disappointed. Instead of antenna farms all I saw were empty fields. Either there were no antennas or someone paid off Google to hide them from prying eyes.

Google Streetview image of VE3VN, dated August 2014

Of course it's the former reason. Acquiring satellite imagery costs money and fewer people want to explore open tracts of land than urban areas. Images of rural areas are infrequently updated to manage business costs. Looking closely for the dated watermarks confirmed this. The satellite images were quite old, predating tower construction.

Google Streetview did better, when their camera-equipped vehicles drove down those rural roads. Even there I ran into a peculiar problem. When I turned a corner the number of towers changed! I backed up and looked at the dates of image acquisition. They were different by two years. Less travelled dirt roads were covered later by Google.

The Streetview capture of my QTH is just above. It is dated August 2014, which is just after the DMX-52 was installed in July but does not yet have any antennas, which went up in September. Here you can clearly see wire antennas. If you are lucky and a recent Streetview image is available it can easily be superior to satellite images.

So go ahead and give it a try. Test your detective skills. See if the antennas some ham is bragging about are as advertised. They may be downplaying their size in an attempt to lull competitors. Now we have the tools to check on them from the comfort of our shacks. Satellite images are also useful for exploring land for a future antenna farm.

2016 - Changes Afoot

2015 was a pretty good year for me in amateur radio. I continued to have good success in the major contests running QRP; DX results rolled in; antennas were improved; and multiple purchases of antenna-related hardware put me in good stead for my future plans.

I expect 2016 to, at first, unfold in a predictable fashion. There are contests to enter and DXpeditions to work. The rest is tentative. This may be the year that I move to an acreage and build a proper antenna farm. It is what I've been planning for. Yet there is always more to life than amateur radio, so other priorities may intrude and cause delay. Since those are all no more than possibilities as of now I am free to follow my amateur radio ambitions for the near future. I place the probability of a move this year at 70%.

First a brief recap of 2015 events at VE3VN, in particular how I did in relation to my plans at the start of the year. I'll mostly skip over contest results and the like since that is certainly of little interest to anyone other than me. Should you wish you can compare how I did in comparison to my plans and expectations.

2015 retrospective

My earliest act was to purchase a FT-1000MP so that my daily operations would no longer be QRP. However I continued to operate QRP with the KX3 in major contests. My reasons for this are simple enough:

• I have lots of QRN from my neighbours lights and other appliances. This is a plague for many hams these days. With QRP there is a virtual guarantee that any station that answers my CQ in a contest is one that I'll be able to hear! At 100 watts or more that is not true, even with good receive filters.
• With small antennas I can be more competitive in the QRP class. Hams with better antennas rarely operate QRP. It does happen, and when it does I lose badly. But mostly I am able to compete with others similarly equipped.
• There is virtually no possibility of being an RFI hazard for my neighbours when I operate flat out for 24 or 48 hours contests. Since I appear to have had no issues at 100 watts I expect to do more low power contesting this winter.

I extended my activity to new bands. I returned to 6 meters for the summer sporadic-E season. Even with a small, and compromised yagi I was able to work several countries in Europe and the Caribbean. Using the internal transceiver tuner I made my first QSO on 12 meters at year end, and similarly worked several stations on 6 meter aurora propagation.

As planned I made small but important improvements to my low band antennas. My activity, and results, on 80 and 160 meters increased with my new 80 meter vertical. Although not resonant, the vertical works better on 160 (with the rig's internal tuner) than what I could do before. The new 40 meter inverted vee worked out better than expected since it does better to Europe than the old inverted vee.

Progress toward my future antenna farm went quite well. I now have in storage a 150' commercial-grade guyed tower, a 2-element short yagi for 40 meters and 2,000' of Heliax. I chose to forgo other opportunities since it is too difficult to move and store large amounts of hardware with my current living arrangements. There will always be other opportunities.

2016 plans

There will no new antennas at this QTH in 2016. My energies will be directed toward my next QTH. Tweaks to current antennas are acceptable but that's it. If I do put my house on the market it is likely that the towers and antennas will come down sooner rather than later, and probably no later than early spring. That's only a few months away!

Other than the truly unexpected it is only events in my personal and professional life that are likely to stand in the way of my radio ambitions. There is the possibility that I will have to stay in the city for at least another season if certain matters develop.

Inside the shack I intend a few experiments to pave the way to future improvements. The FT-950 (an interim and adequate rig) is part of that plan since it is better for contest work than the FT-1000MP it replaced. I am deferring the purchase of a top-end transceiver until I am out of the city, since local QRN prevents me from hearing better at this QTH. A good receiver would be wasted. I am leaning toward the Elecraft K3S, but I remain flexible in case something more suitable comes on the market when I am ready to buy.

This year I will experiment with more station automation, such as computer integration and multiple rigs, to bring my contesting abilities to a more modern standard. Constraints I face include my operating desk, which is not computer friendly; for example, there is no good place to mount a monitor. Another constraint in the ancient laptop I use in the shack: it's under-powered for more than basic contest logging; and has only 3 USB ports. But it does have battery backup. Changes may be deferred until after I move.

As for contests, as I hinted after CQ WW SSB my interest in QRP class is waning. For SSB especially but also for CW. I intend to do more contesting with 100 watts even though I have no hope of placing well with my small antennas. Consider it as ongoing training for when I do have better antennas. This is one of several reasons why I replaced the FT-1000MP with a FT-950.

At least I'll be leaving QRP with a bit of a bang. From an early view of my log check report I will repeat as world #1 in SOAB QRP in CQ WW SSB. For the CW weekend I hope to repeat as #1 in North America, and should do so unless my error rate is high (quite possible since I was not at my best that weekend).

While I am not a fervent DXer I very much enjoy chasing rare DX, whether or not they're countries I need. Since returning to the air in early 2013 I have worked 260 countries. I chose to restart my count rather than include what I worked before 1992, including some very rare ones. Not only would the paperwork of doing a combined tally be unpleasant (I also dislike QSLing, and avoid it when I can) I found it interesting and motivating to start over from zero rather than 300+.

Upcoming DXpeditions to VP8, KP5 and possibly P5 are on my calendar for January and February. I hope to work them on as many bands as possible. P5 would definitely be an all-time new one (ATNO) for me.

Blog and contact info

Activity on the blog should continue at a similar pace in 2016. I see that I average one posting a week, and that seems to strike the right balance between use of my time and how often I have anything of interest to say. Should I move this year expect a lengthy interruption.

Although I have no new antennas planned for this QTH (assuming I do move this year) you can still expect antenna articles -- more in the way of modelling rather than construction. Many of these will be focussed on larger antennas for the planned future stations, with excursions to related topics. Expect more about 40 meter yagis in particular.

This year I've resolved to consolidate the diverse email accounts I use for personal and professional activities. Although some of you have seen how one or more of my addresses resolve to another account, you should not use that account. For the present you will get best results using my call sign at rac.ca. There will be no announcement when I discard obsolete email accounts.

In closing

A few days ago, as I was listening to a few of the northeast US super-stations working Asia long path at sunset on 40 and 80, the lights around the neighbourhood turned on and blanketed the DX with the pulsations of cheap switching power supplies. It was very frustrating, even though I had no hope of working those Asians with my small antennas and 100 watts. I hope to leave all (or most) of this behind when I leave the city. It's one more motivation to accelerate my retirement plan.

I was out of the hobby for over 20 years while I pursued other life objectives and ham radio was an unwelcome distraction. Since I've rediscovered my love of the hobby I realize it has to be a bigger part of my life. The passing of friends and family during the past year drives home the message that for all of us time is limited. If I don't pursue my dreams now then when? The golden age of baby-boomer driven amateur radio activity won't last forever. Right now may be as good as it gets for contesting and DXing.

Winter Doldrums

Winter has been delayed. As I type this it is 17° C and sunny. There is also a gale blowing from the southwest, bringing this warm and moist air to this northern region. To give you an idea how anomalous this is, the normal high for today is -3° C and the previous record high is 8° C. Instead of being knee deep in snow the lawn is green and lush. If I had antenna work to do this would be ideal weather for it. Well, except for the wind. Except that I'm done with that for 2015 so all I can do is enjoy the warmth. It won't last.

On the bands the activity is there but not too much of great interest. It's possible to tune for many kilohertz without hearing a single signal, even when the band is certainly open. There is also the recent CME (coronal mass ejection) and subsequent series of X flares that have dampened HF conditions, discouraging for DXing. The Christmas season also brings a temporary lull in activity. There are no major contests right now and a few major DXpeditions will not take to the air until January. Dom, P5/3Z9DX, was impossible from here with the CME obliterating the over-the-pole path.

This is a good time to catch up on a few things that are not related to intense on-air activity. These winter doldrums have their uses. Not all has been quiet at VE3VN.

The RAC Winter contest was a nice way to spend part of last weekend. For me it was a relaxed way to spend some hours handing out contacts and saying hello to many acquaintances. I had no competitive objectives. Running 100 watts rather than QRP, and being worth 10 points, made for some decent runs on both CW and SSB. It was a low pressure opportunity to practice running and managing multiple simultaneous callers, with rates at times peaking at 5 QSOs per minute.

As it turned out this contest operation was the last for the FT-1000MP I purchased less than one year ago. On Sunday I delivered it to its new owner. In its place I have a Yaesu FT-950. Like the FT-1000MP this, too, is a temporary rig. I am delaying purchase of a new, top end transceiver until I am in a situation where I can do better than with my current QTH and station. Although things can change this is likely to happen in 2016.

As to why I went with the 950 in lieu of the 1000, I have several reasons, despite the loss of some valuable features.

• The FT-1000MP (Mark V Field) I bought has no optional filters. Just the 2.7 kHz filters in both receivers and a 500 Hz CW filter in the main receiver. Purchasing Yaesu or INRAD filters to meet my operating needs is not inexpensive, even if bought used. I do not want to invest more into this rig, with its 20-year old technology. The DSP filtering in particular is poor; a full complement of crystal filters are necessary to achieve good performance.
• The FT-950 has poor roofing filters (typical with an up-conversion superhet receiver) but does have decent DSP filtering. There is ringing at its narrowest 100 Hz bandwidth, though it is not very objectionable at 200 Hz and higher. In contrast, the more modern Elecraft KX3, my QRP rig, has ring-free DSP.
• The FT-950 receiver tests better than the FT-1000MP and many other, even more expensive rigs. Under duress, with narrow spacing from a strong interfering signal its measured performance is less impressive. This is likely due in part to the wide 3 kHz roofing filter. Even with W8JI's IMD mod I am not convinced the FT-1000MP does as well as the FT-950. I could be wrong.
• It is convenient to have 6 meters included. This way I don't need to switch to the KX3 and external amplifier, and put up with the poor behaviour of the KX3 on that band. The first few QSOs I made with the FT-950 were 6 meter aurora to the HF tri-band yagi, using the internal tuner.

Features of the FT-1000MP I most miss include: second receiver and more features accessible from the front panel rather than hidden in menus. I accept the trade off.

The noise blankers in both rigs are less than great, with the one in the 950 not reducing much of the impulse noise I experience and the 1000 causing unacceptable distortion. The 15 choices of noise reduction in the 950 tell me that Yaesu has no idea which ones are worth keeping, leaving that up to you. A few are useful, most are not. CAT on the 950 is faster and integrates slightly better with the logging software I use.

Apart from that I have been doing some maintenance on the mechanical drive for the prop pitch rotator. It's in generally good shape and so is almost ready for use. Its years of use and subsequent outdoor storage took a toll that requires some work before being called upon for more years of service.

There may be one more article for this blog before year end. Early in January I plan my usual retrospective on the year past and plans for the new year. If all goes well 2016 will bring significant change. Enjoy the holidays, have a merry Xmas and perhaps I'll run into some of you on the air.

40 Meter 3-element Yagi: Matching vs Optimization

Yagi performance can be pretty well summarized by the following metrics:

• Gain
• F/B
• SWR

We can model or measure these, across the band of interest, and then compare to make the choice that suits our individual needs. In all cases we should take care to account for and, if possible, minimize losses due to ground, conductor resistance, load equivalent series resistance and matching network. This is as true of all antennas, including dipoles and verticals, not just yagis.

As a general rule you can optimize the performance of a yagi, though usually only of one or two of those three metrics. As you move lower in frequency the optimization challenge increases since the bands grow quite large when expressed as a percentage. Good performance at one frequency is a poor indicator of performance across the entire band.

• 20 meters: 2.5%
• 40 meters: 4.3%
• 80 meters: 14.3%
• 160 meters: 11.1%

For the lower HF bands the challenge is usually a bit less than stated since, in some parts of the world, the bands are narrower, or we are primarily interested in a narrower slice of spectrum. For me these would be 7.0 to 7.2 MHz (2.9%), 3.5 to 3.8 MHz (8.6%) and 1.8 to 1.9 MHz (5.6%). Even so it is difficult to optimize antennas for these wide bandwidths.

In this article I'll focus on a 3-element, full-size yagi for 40 meters. Getting good performance over the entire band, even up to 7.3 MHz, is achievable without excess compromise. If you've been a regular reader you'll know that 40 meter yagis are of specific interest to me. If your interest differs the lessons can be applied to yagis for other bands.

The model of the yagi is kept simple in this exercise:

• Boom: 15 meters. This is slightly longer than the standard 48' boom for a 3-element full-size yagi.
• Elements: 40 mm diameter tubing. Correction for taper can be included before a design is turned into a construction template.
• Driven element position: Unless specified otherwise, it is slightly offset from centre towards the reflector by 0.2 meters. This provides clearance from the boom-to-mast bracket and usually nets a small amount of additional gain.
• Parasite tuning is specified as ±X% for a selected centre frequency. The centre frequency is with respect to gain and F/B frequency positioning, not resonance or matching. This method of tuning parasites must not be used for shortened parasitic elements, whether by coil, capacity hat, trap or other technique.

With that preamble out of the way let's dive into some design.

Optimizing the yagi

Gain in a yagi is determined by two parameters: boom length and parasite tuning. You then only need elements distributed along the boom so that there is sufficient coupling to fully exploit the boom length. The tighter the parasites are tuned (small deviation from resonance), the greater the gain. The driven element only affects gain and F/B a small amount, mostly determined by its spacing from the reflector and first director. We are free to adjust driven element length (within reason) in pursuit of a good match.

I first learned these lessons a long time ago from W2PV in his excellent book Yagi Antenna Design. The book is out of print, but well worth picking up on the used market. In a few pages of graphs he illustrates the performance differences in yagis with various boom lengths, element spacing and parasite tuning. Although we now have better modelling software his presentation of the material is still top notch.

Unfortunately, as we maximize gain, while the F/B may suffer somewhat, the SWR rapidly becomes a problem. The reason is that high gain is associated with low radiation resistance. By Ohm's Law this means increased current. The higher current is partially responsible for the increased gain. It is also responsible for increased I²R loss. In a yagi with shortened elements, whether traps and coils, there can be considerable loss. There typically is negligible loss in HF yagis with full-size elements, due to the large diameter tubing. However, whether the elements are short or long the low radiation resistance makes matching difficult.

With loose parasite tuning the matching problem is easier to solve, at the expense of gain. F/B will generally remain good. An example is the optimized 3-element 40 meter yagi presented in the ARRL Antenna Book. The SWR is kept below 2 across the band, and F/B is good, but gain is sacrificed. This is due to the wide ±7.3% parasite tuning. The reflector is 7.3% longer and the director is 7.3% shorter than resonant length at the centre frequency.

Tightening parasite tuning to ±3% gives us a gain greater than 9 dbi (in free space) across the band. This is almost 1.5 db better than the ARRL design. The downside is a very low radiation resistance of ~12 Ω, which is difficult to match and only allows a 2:1 SWR bandwidth of 125 kHz. Optimizing for gain prevents optimizing for match.

If we loosen parasite tuning to around ±6% the radiation resistance rises to ~24 Ω, which is easier to match to 50 Ω coax and increases the 2:1 SWR bandwidth to 200 kHz. Gain is almost 1 db better than the ARRL design.

The charts at right plot the impedance components (R & X) for the tightly-tuned yagi optimized for gain versus the more loosely tuned yagi. The gain difference is between 0.5 and 0.75 db, and falls to nil at 7.3 MHz. F/B is slightly better for the gain optimized yagi at the high end of the band.

As is typical for 3-element yagis the peak F/B is below the design frequency and the peak gain is above the design frequency. The parasites can be tuned in tandem to shift these curves to where you want them. I chose 7.1 MHz as the design frequency since the resulting F/B and gain curves best meet my needs.

As should be obvious from the impedance chart the radiation resistance is the reason for the reduced bandwidth of the gain optimized yagi; the reactance curves are similar. To best transform the impedance to 50 Ω it helps to have the ratio of X to R as small as possible. This is why the SWR bandwidth of the gain optimized yagi is so poor. Even for the loosely tuned yagi the SWR bandwidth is only 2/3 of the band. That is, in North America; in Europe it will cover the entire 40 meter band.

Some improvement is possible with larger diameter tubing since the reactance changes less with frequency. That is impractical for a 40 meter yagi, for reasons of expense, weight and wind load. In any case the improvement too small to be worth the effort.

The model uses constant diameter aluminum tubing, which is clearly unrealistic. Tapered tubing will alter the element tuning but, after adjustment for the taper, the performance results will not be appreciably different. Since this is a preliminary study, not a construction article, I kept the model simple.

Passive matching networks

There are several common matching networks used to transform the impedance to 50 Ω. They are all similar in that they use transmission line sections in combination with an off-resonance driven element to construct what is, in essence, an L network with a shunt inductance and a series capacitance.

• Beta (hairpin)
• Gamma
• T
• λ/4 transmission line transformer
• λ/12 series transmission line transformer

Gain and F/B performance are only negligibly affected by these matching networks. The gamma and T networks are often preferred in large yagis since these do not require insulating and sectioning the driven element for a dipole feed.

Using EZNEC I modeled a few of the aforementioned matching networks. The matches they deliver are indistinguishable. The only real difference is due to an offset in the curves of ~25 kHz that I was too lazy to tune out in the model. Since the gamma and T are more difficult to model with EZNEC, and will have a similar results, I chose to omit them.

An L network made from coils and capacitors would be little different. Actually it would be better but the difference is so small as to be inconsequential. The lesson is that if you use a passive matching network you should choose the one that is easiest to build and adjust, or that has some other feature you value. For example, a gamma match doesn't require the driven element to be split or insulated from the boom. In a 40 meter yagi this can be advantageous.

I modelled the λ/4 transformer with two parallel 6.93 meters lengths of RG-11 (35 Ω). The λ/12 sections are 2.31 meter lengths of RG-213 connected to the driven element, and two parallel 2.31 meter lengths of RG-213 (25 Ω) from there to the 50 Ω transmission line. Parallel matching sections of these types can be constructed with two T-connectors. The beta match hairpin is 1.1 meters of 300 Ω transmission line (1.0 μH) made from aluminum tubing. The driven element shortened to centre the SWR curve.

All these feed systems require a common mode choke or suitable 1:1 balun to prevent common mode current on the transmission line and, likely, degraded F/B.

Active networks

To fully tame the SWR at the feed point an active network can be used. This can be something quite simple if "good enough" results are acceptable. To demonstrate, I took the beta match design from above, which gives a low SWR in the lower part of the band, and added relay activated components at the feed point.

It was quick work in EZNEC to experimentally find the component values I wanted. A pair of 1,500 pf capacitors in series with each half of the driven element lower the SWR below 2 in the high end of the band. You should not use only one capacitor since that would unbalance the driven element. A DPST relay (or a pair of SPST relays) unshorts the capacitors. Use the opposite arrangement (normally open relay contacts) if you primarily use SSB. The capacitors should be transmitting "door knob" type for this high power application.

Alternatively, coils can be used instead of capacitors, if you find they are easier to work with. In this case we would leave the tuning the driven element as before and short the coils when operating above 7.2 MHz. I didn't bother to calculate or model the required coil values.

The SWR does not dip as low as in the passive network since the capacitors (or coils) alter the matching network, and do not simply cancel the capacitive reactance of the shortened driven element. A fully switched network, with coils and capacitors, is needed to optimize the SWR for both switch positions. I chose to keep it simple since that is sufficient to my needs.

A remote or shack-based tuner can also be used. If you choose this active tuning option you ought to calculate the transmission line loss due to the high SWR. Low loss transmission line (e.g. Heliax) may be appropriate.

Coupled resonator

There is another method of achieving a broadband match: the coupled resonator. This requires another full-size element that is tuned to a higher frequency than the driven element, and is positioned close to the driven element. Parasite position and tuning remain unchanged.

A coupled resonator should not be confused with a Moxon. Here the coupled resonator is equivalent to a second driven element. There are designs that use dual driven elements to extend the SWR bandwidth, but a coupled resonator is simpler.

By virtue of the tight coupling with the driven element the current is, in a fashion, split between them. With the subsequently lower current the feed point resistance is raised. By careful tuning and positioning of the driven element and coupled resonator the antenna can present a low SWR across the 40 meter band.

Note: Some label the coupled resonator the first director. That is misleading. True, it is a parasitic element. However it has little impact on gain and F/B when inserted into a conventionally designed yagi. The difference it does make in this respect has more to do with the current distribution, which effectively alters the spacing between the (dual) driven element and the adjacent parasitic elements.

The preliminary design I came up with places the two elements 1 meter apart, each 0.5 meters from the boom centre. The driven element is lengthened to resonate lower in the band and the coupled resonator high in the band. Current in the coupled resonator is 45% that of the driven element at 7.0 MHz and rises steadily to 105% at 7.3 MHz where it is close to resonance.

SWR is below 2 across the band. It was necessary spread the tuning of the parasites a small amount to tame the SWR above 7.25 MHz. However I only gave up 0.1 db of gain and actually improved the F/B compared to the yagi designs discussed earlier. Better results should be possible.

I did briefly attempt to use a coupled resonator to match the gain optimized yagi, with only partial success. I could not get the SWR below 2 across the entire band, but did increase it to over 200 kHz, as compared to the 125 kHz with a conventional matching network.

Although this design "works" it is in no way optimum. This is merely an early attempt to test the use of a coupled resonator in a large antenna of this type, and form a base from which to test other designs. There are commercial antennas that use the same concept, and there are the WA3FET OWA designs that have gone through a substantial amount of optimization. If the concept intrigues you, check those out. Perusing the web I noticed that K9CT has an antenna that is similar to the above design. Yes, it's very big!

The driven element requires a dipole feed: split element and isolated from the boom. The coupled resonator can be mounted directly to the boom. A common mode choke or suitable 1:1 balun is required to prevent common mode current on the transmission line.

The main disadvantage of the coupled resonator is the mechanical load and cost of the additional element. For most it may be better to use an active matching network as discussed above.

Choices

Modern contest stations value flexibility. There is an attraction to a high-performance 40 meter yagi that requires no tuning of station equipment, transceiver or amplifier, when changing frequency or when switching antennas. An assured low SWR under all situations delivers that flexibility.

As we've seen there is a price to be paid for this flexibility. It comes as reduced gain, higher cost and physical size. What would be acceptable on higher bands is less so on 40 meters. Yet it is a band that requires high performance if one is to do well in contesting, and in competitive DXing. This is increasingly true as sunspots continue to decline over the next few years.

Well, for the interim I do have an XM240 in storage, ready to be raised once I have a QTH and tower in place. That antenna is ultimately intended as a second antenna for 40 meters. So I plan for something larger as the primary antenna. The work I've done for this article is part of that planning.

To summarize, here are my choices as I see them:

• Wind and ice load: The coupled resonator design adds substantial load. Even so it is arguable that one more element added near the centre of a full-size yagi is not a large step to take.
• Cost: Full-size elements and more than 3 elements substantially adds to the cost of the antenna. That is, if the antenna is to survive the elements and be reliably available when contest weekends arrive.
• Matching: Active and passive impedance matching options each have their pros and cons. Passive, low-SWR broadband matches are preferable. This favours the coupled resonator. A switched set of loads to extend the range of a conventional matching network may be my best choice. Initially I could use low loss coax and a tuner in the shack. The tuner could be bypassed for operation between 7.0 and 7.2 MHz. A coupled resonator can be added later if I decide to take that step.
• Gain: Sacrificing less than 1 db of gain for a better match is acceptable. I will avoid sacrificing more than that.

When I next revisit this topic I will look at the possibilities of long boom yagis with shortened elements. These are popular antennas since the gain sacrificed is compensated by substantially less cost and wind and ice load. But it can get complicated.