Fallow Summer

My on air activity is limited at the moment. This is partly due to the arrival (finally!) of warm spring weather. There is so much to do that the weather makes attractive, both radio and non-radio related. The other part that makes me relatively inactive is a lack of antennas. That may sound odd when you consider the number of towers and antennas that I appear to have. But there are reasons.

The new big tower was raised to 120' in early May with the help of Eric VA3AMX and my regular assistant Don VE3DQN. The top 20' are waiting for my decision on a rotator. I will then fabricate plates, machine the mast and select bearings. There is no rush since the stacked yagis for 20 and 15 meters that will go on it are not ready.

In the background you see the 150' tower. The TH6 and XM240 up top have intermittent problems and so they must come down. I wanted to do this before the hay got too high (and the ticks emerged) but is delayed until the hay is harvested. I could not arrange a full ground crew and rig the tram line in the short window after the new tower work was completed.

Once they are down and repaired the XM240 may end up in its original position atop the Trylon tower at 21 meters height, below the 6 meter yagi. However this depends on whether I can build and raise a new 40 meter yagi onto the big tower before winter. It will be a challenge. The TH6 and TH7 will be stacked at a low height on one of the big towers to cover North America.

The 160 meter vertical is disconnected and the radials rolled up, again in consideration of the haying. To simplify redeployment this year I left it tied to the tower top and secured the wires to a guy anchor to keep them from tangling with farm equipment.

My 80 meter yagi project suffered a setback when the stinger for the driven element broke and the top half speared into the ground. After putting it up I discovered that the column (compression) strength of the stinger was insufficient to withstand the tension on the rope and wire supporting the parasitic elements.

My hope was to delay replacement, but it must now be dealt with before I can resume work on the yagi switching system. The job is not difficult just annoying, especially since I was making good progress on the direction switching system construction and installation. In any case the low bands are not attractive during summer due to the high noise level.

Inside the shack there are also problems. One is that the recently acquired Drake L7 amplifier has a couple of faults. One is the T/R relay (a common failure point) which has intermittent high contact resistance on receive. My gentle cleaning temporarily cured the problem but now I must take more aggressive action. Eventually I will replace the open frame relay with something faster and quieter.

The second fault is the loading variable capacitor. Occasional arcing on the low bands led me to discover that several rotor plates are not straight and get too close to the adjacent stator plates. With the capacitor pulled pulled from the chassis I found that it had been previously worked on, and not very well. The repair is easy but time consuming. Again, there is no urgency since I am relatively inactive during the summer.

Last weekend was CQ WPX CW. Although it is not one of my favourites I wanted to play around for a while with high power. Since that wasn't possible and because of the antenna situation I opted to enter as 20 meter low power. It is perfectly possible to have a few hours of fun with a crippled station.

The one antenna I do care about right now is the 6 meter yagi. At least that antenna is trouble free. If only DX conditions were better. Sporadic E season started well but has entered a lull in this part of the continent.

I'll have more to say about yagi construction when I'm further along in that project. The bulk of the required aluminum is in hand and machining of the tubes has begun. I want the yagis ready to fly in August for testing and adjustment after the hay is harvested and it is easy to move around the fields. This project will keep me busy since with my lack of antennas (and sunspots) there is little incentive to spend time in the shack. Well, at least when 6 meters isn't hopping.

Reflections on Doing Business

Building a middling large contest station necessarily involves lots of spending. It adds up quickly. Consider the following (partial) list:

• Station equipment: rigs, amplifiers, switching, rotators, antennas
• Electronic components
• Materials: steel, aluminum, concrete, wood, PVC
• Fasteners: clamps, screws, guy hardware
• Services: welding, machining, heavy equipment, steel work
• Cables: coax, wire, electrical

That's a lot of business! Even when you build much of it yourself as I am doing there is an endless list of items to be purchased. For most of us who are not wealthy it is important to develop and work to a budget to avoid frustrated ambition.

Let's look at a few examples of doing business while building my station. There are lessons for us all, positive and negative.

Tower services

The commercial tower business is thriving. Most is done by large enterprises that have multiple locations and remote management. They are the least flexible in working with hams. Small local outfits are far easier to deal with. When I first moved to this QTH I made a point of dropping in to see the local tower service company to get to know them and see where they might be able to help me with my station. I knew a few hams who had hired them and were happy with their performance.

You might not be so lucky but unless you take the trouble to look them up you'll never know. They put in the foundations for both my big towers. Although there were a few problems they took the extra effort to resolve them. Some of these were due to miscommunications, such as their expectation that I knew more about dealing with heavy equipment better than was the case.

They have become a good source of surplus equipment and material from decommissioned towers and communications systems. I make a point of recommending them to others and I continue to give them them my business.

Aluminum

Buying antenna aluminum in Canada is a challenge. Although we have a huge aluminum industry the selection and availability of many types of aluminum tubing is often not friendly to hams. The 0.058" wall tubes that assist with telescoping yagi elements are almost unheard of despite being widely available in the US. These are considered aerospace material. Importing long tubes is far from economical.

On the other hand aluminum tubes and other shapes are widely available and economical if you are willing to improvise with more common sizes. I've modified my yagi designs in accord with local availability. All I'm then left with is finding the best company to work with.

My first experience several years ago was barely adequate. The company that seemed best had a limited selection and they only dealt in full lengths, typically 20'. Cutting to size was expensive. They catered to industry and barely tolerated retail customers. But the prices were excellent.

Several months ago I went to another firm that makes a big deal of their selection, cutting to small quantities and walk in retail customers. Again, the result was not great. For my second order I selected a small quantity of short tubes to test in my workshop for suitability to build yagis. Every tube in that order was wrong, either OD, ID or alloy. I gave up on them for good.

I returned to the first company. On the phone they were far more receptive than I remembered so I dropped in to see them. What a change. They worked hard for my business including hunting down non-stock items and discounting the price for the quantities I needed. The order was filled to perfection.

When I had difficulty loading the tubes into my car the company president offered to deliver it to my place, despite the bother and the 100 km distance. It was delivered in good order the very next day. On being asked to think of them in future I told him I certainly would.

Like people, companies change. Don't be afraid to try again long after a poor experience. Companies that survive must change to stay competitive.

Wire and cable

In my station there are ~500 meters of coax, 2000 meters of wire, 1300 meters of guy strand, 500+ meters of control cable, plus guy grips, junction boxes and much more. I buy very little of it at the better known retail outlets. Some was bought used, most was bought new and I've acquired quite a lot for free or close to free.

After shopping around I do most of my buying at a local branch of a province wide supplier of electrical equipment to trades and industry, including power companies. Their prices and selection are good and they make an effort to special order what they don't stock locally or their central warehouse. They are happy to sell small quantities to retail customers, although they prefer large quantities.

When there have been errors and other problems they always try to make good, albeit grudgingly at times. I'll keep going there for as long as the good experiences predominate.

Welding and machining

There are welders everywhere. In rural areas like mine there is a sign hanging out front every few kilometers where small operators work out of their homes. There are almost as many commercial enterprises with 2 or 3 people. Then there are the large companies that cater to industry. Machinists tend to be collocated with welding shops since they are closely associated despite being distinct trades.

I went by recommendation rather than hunt one on my own, choosing the shop that did the welding for the guy anchors on my first big tower. The proprietor is a machinist and his partner is a welder. This is where I went for my custom guy yokes, tower load bearing plate and trimming aluminum pipe for booms.

A misunderstanding led to incorrectly bent plates for the yokes, which they corrected by making new ones from their own metal stock. Aside from that error the quality of the work is excellent and the prices reasonable. I intend to return to them to fabricate steel plates for the mast bearings and rotator needed for the new tower.

Specialty markets: retail and swap nets

The specialty amateur radio market in North America is going through a secular shift as older generations age out and the type and quantity of business changes. In Canada several ham market retailers have closed down in recent years and the ones that continue have branched out into other lines of business to survive. It's a tough sector to be in.

At a flea market this spring it was obvious that our hobby is approaching a crisis. A friend and I surveyed the crowd and saw an almost uninterrupted panorama of male grey heads. That isn't sustainable. Among the items on my table the old stuff interested old people. More recent technology drew in younger hams. By younger I mean in their middle years.

It won't be long before the smaller ham flea markets fade away. That's a shame since they can be very enjoyable events.

Online swap shops suffer from the same ills of all online fora: swindlers. This was far less common when swap shops were in print or on air. The bad actors are mostly small time criminals and scammers that infest all branches of online person-to-person commerce. A few are hams. Due diligence is required on every deal, whether you are a buyer or a seller.

Lessons learned

It is well worth the effort to find and stay with companies that are reliable, fair and willing to take the trouble to keep customers happy. For most of these companies the business from a ham is small in comparison to their industrial clients. Since many can't be bothered with small retail customers it is important to appreciate the one that do.

Although ugly stories abound most people are reasonable and reliable. Doing business can be enjoyable with the right person or company on the other side of the deal. Don't let yourself be ruled by cynicism: many people are their own worst enemies. When you mostly have bad experiences doing business it's probably you not them. Don't be one of "those" customers.

Strive to build strong long-lasting business relationships. Treat a first deal like a first date. Trust builds over time. Excuse a few lapses since we all make mistakes. But move on when it becomes a habit.

Do you need a recommendation for a supplier or service? Ask the people you've come to trust doing business with. One of the reasons they're good is that they rely on other good companies. They'll lead you to the good ones. That's how I've had success finding the dealers and services I've come to rely on.

Prime Time 6 Meters

Summer is coming.

The solstice is less than 6 weeks away and E_s (sporadic E) season is well underway. As I tell everyone I know with a passing interest in 6 meters mid-May is when the DX starts to roll in. Indeed the DX has been heard here since early in the month.

This is the DX I've heard so far on 50.313 MHz and 50.323 MHz FT8:

• Europe: EA, F, CT
• Africa: EA8, 5B
• South America: PY, YV
• North America: VP9, J8, KP4

Some signals have been excellent and in for several minutes at a time. Here is one example:

I have not worked any DX as yet. The interesting stations have been weak or fleeting while the strong ones I've worked before and did not want to get in the way of the many trying to work them, perhaps for a new one. Further east in W1, VE1 and VO1 the openings have been better than ours.

Chances are you have an HF transceiver with 6 meters. Try loading up any HF antenna with the ATU and give it a try. It doesn't take a lot of power or a lot of antenna to have some fun. This is prime time 6 meters. It will continue until early August, peaking in late June. Go ahead and give it a try. If you are already active on 6 meters be on the lookout for those elusive DX openings.

Have fun and I hope to see you on the magic band.

Yagi Elevation Angle Nulls: Tilt & Fill

A common source of ideas for this blog is other hams. When a recurring question came up recently I thought that it would make for an interesting article. The question is: can you fill in those elevation angle nulls in a yagi pattern by tilting the antenna up? The short answer: no.

More interesting is why it is true since it can teach us about how antenna patterns are what they are. In this article I'll dig a little deeper and discuss its implications, including how to go about filling those nulls. I believe it is worth the effort since you can be held back in the achievement of your operating goals if you ignore pattern nulls.

Yagi tilt in free space

Ground is responsible for the existence of elevation nulls. Before we go into that we should have an understanding of a yagi's free space pattern where ground plays no role. Only then should we bring ground into the picture.

I am using EZNEC to do the models and pattern generation. I am use its features to easily rotate antennas and to compare patterns by overlaying them on one plot. Since I have 6 meters on my mind these days I returned to my optimized A50-6 model to provide the examples. It has enough gain that the main lobe is not too narrow nor too wide, helpful in illuminating the current topic.

In free space the main lobe (looking forward along the boom) is a bulb shape. With no ground reference the 15° tilt has no effect on the pattern. Of course the same is true for any amount of tilt, for any direction or boom rotation. Just as for astronauts in space there is no up or down.

Ground reflection

The pattern of a horizontally polarized antenna over ground is the sum (interference pattern) of the sky wave and the ground reflection. The relative phase and amplitude of the two determines the flux in every direction. Since we cannot transmit a signal into the ground we can safely ignore the half sphere of the pattern below a plane tangent to the ground. EZNEC automatically trims it.

We can now return to a comparison of the two antenna patterns. Because height affects how the ground reflections sums with the sky wave I am using the actual height of my antenna, which is 24 meters (80'). I've made the elevation plot large and used a 1° step size so that detail can be seen.

There are a few features of the pattern comparison that stand out. First, gain of the tilted yagi decreases at low elevation and increases at high elevation. This should not be a surprise. The antennas have equal gain at 35°. The second and perhaps most important feature is that the elevation angles of the nulls are identical. All that has changed is the depth of the nulls, which are shallower for the tilted yagi. The third and equally important feature is that the nulls of the tilted yagi are increasingly shallow at high angles.

To understand what's going on we need to refer back to the free space patterns. Gain is equal for equal positive and negative elevation angle deviations from 0° elevation due to pattern symmetry. Therefore when ground is parallel to the yagi ground reflections are therefore of similar amplitude for equal positive and negative angles. Reflection gain (nominally 6 db) and null depth depends on ground quality which determines reflection loss and, at low elevation angles, reflection phase shift.

Maximum gain and maximum null depth occur when the amplitude of the reflected wave is equal to the sky wave. Lobe peaks are at elevation angles where the phase difference is 0° and nulls occur where the difference is 180°. The higher the antenna is above ground, as measured in wavelengths, the greater the number of minor lobes and nulls. The 0° null is due to phase reversal of reflections at low incidence angles over imperfect ground.

Tilting the antenna does not affect behaviour of ground reflections. What does change is the amplitude of the reflections. Since the yagi main lobe is no longer symmetric with respect to 0° elevation the sky wave and ground reflection amplitudes are no longer equal for equal positive and negative elevation angles. For the modest 15° tilt being examined the inequality is greatest at high elevation angles.

Suffice to say this is not what we want. Tilting a yagi upward not only doesn't fill the nulls, except at the less useful high elevation angles, the gain at low angles is reduced.

Terrain

This analysis assumes flat, uniform ground. Complex terrain introduces complex ground reflections that shift the positions of the lobes and nulls, and their heights and depths, respectively. However, tilt still has no particular advantage since the lobe and null elevation angles remain as they are. Ray tracing tools such as HFTA can provide insight into how the terrain affects the elevation pattern.

Ground quality determines the amplitude of reflections, including the elevation angle below which reflections are phase reversed. The latter is why gain is zero at 0° elevation. For horizontal yagis like yagis the reflection amplitudes even over poor ground are reliably strong. Not so for vertically polarized antennas, but we're restricting this discussion to horizontal yagis.

Stacking

A common technique for increasing gain is to stack two or more yagis. Power is split among the antennas with phase set to achieve the operating objective. In almost all cases the yagis are fed in phase.

Another desirable characteristic of stacks is to move or reduce elevation pattern nulls. This is done by taking advantage of the different heights of the yagis (not applicable to side-by-side yagis). The lobes and nulls are different for each yagi alone and when two or more yagis are used. We'll keep it simple by restricting the discussion to two yagis in a vertical stack.

I've kept the first yagi at 24 meters height and added an identical one at 18 meters height, which is 1λ separation, the same as the boom length. Equal separation and boom length usually works well, and in any case we are interested in the general pattern rather than maximum forward gain.

Green is the upper yagi, red is the lower yagi and black is the stack (BIP: both in phase). Stack gain is as expected at about 3 db. The higher yagi has more minor lobes due to the greater height. For the lowest inter-lobe null (marked) the difference among the three is only very small at a little over 1°. The difference increases at higher angles. Unfortunately that first null is pretty stable for all configurations of the stack, so our objective is not met since the lowest null is the most critical for DXing.

The reason for the lack of movement of the lowest null is that the ratio of yagi heights is only 1.3. Small height ratios are typical at VHF and above, while at HF larger differences are the norm. The small ratio is good for gain but not for moving nulls. If this is important at VHF it is desirable to have a second antenna at a lower height. For example, to work single hop E_s at high angles and DX at low angles, as covered in a previous article.

Space

Now then, what about antennas that must tilt upward to target satellites and the Moon? I rarely hear talk about the effects of ground reflections in these communications modes, yet they can be important in some situations.

If you point a high horizontal yagi well above the horizon there is no problem. Ground reflections are negligible because the main lobe has a narrow beam width and little radiation is directed towards the ground. However there are ground reflections for moderate and low gain yagis that enter the picture for satellite passes less than ~30° above the horizon.

Circular and vertical polarization are immune from deep nulls. But many small satellite antennas are linearly polarized, especially those that are hand held. Hand held horizontal yagis are actually less of a problem on low passes because they are close to the ground and the nulls are at higher elevation angles.

So, not a big problem overall. When a null is encountered it tends to be a transitory phenomenon (the satellite is in motion) that may be mistaken for bad aim or incorrect polarization. By the time you adjust the antenna the satellite would have already moved out of the null.

Anyway...

Tilt seems a simple solution to dealing with nulls. Like many simple solutions to difficult problems it does not work. Besides which it isn't easy to accomplish. Do you really want to spec the mechanical design of an elevation rotator for a long boom 20 meter yagi? Leave those elevation rotators where they do something useful: satellite and space communication.