Sunday, October 30, 2016

Siting the Towers and Antennas

With 50 acres of land you might think that I have no constraints on where I place towers. Of the 50 acres, a few are allocated to the house and immediate yard area, 20 are being tilled for hay, and the rest are a mix of forest, bush and swamp.Yet there are always constraints beyond the common one of lot boundaries.

Let's look at the constraints I am most concerned with.
  • Houses: As much as possible you want to maximize the distance from RFI emitters and receivers and to protect against damage or injury should a tower or antenna fall down. In an urban environment this can be difficult. A rural setting opens more options, though limited by the next criterion.
  • Length of transmission lines and control cables: Long conductor lengths are expensive and can incur unacceptable loss. The shorter the better, unless you are working with a large budget.
  • Trees, fences, utilities and other barriers: Much grief can be avoided by siting towers and guy anchors out in the open. The closer they come to roads, utilities and trees the greater the risk of accidents. Trees can be deceptive. Their roots can grow out sideways, especially over rocky ground, and a small tree will grow into a threatening giant. Obstacles will also impede the raising and lowering of all but the smallest antennas, and may require a tram from a more distant patch of open ground. And as they say, call before you dig. Do you know where all your utilities, drainage pipes et cetera are buried?
  • Tillage: In a rural setting the conversion of perfectly good land from crops to antennas can be scandalous in the neighbourhood. In some jurisdictions it can even be illegal. If you are in this situation be very careful. For example, the tillable land on my property (~20 acres) is hayed by a local farmer. I want to site and orient the towers in a manner to maximize his access to the land. They will appreciate the gesture.
  • Rock: In this part of the world rock is a frequent excavation impediment. At my previous house my 1985 tower requires breaking through 3' of shale to achieve the required depth. The same had to be done when I built a new house in 1992. Excavation equipment to break rock is expensive. At my new QTH the rock is managable by hand digging for the self-supporting tower, but that was due to careful site planning: I chose a location with perhaps 2' of well-settled soil above the natural grade. Avoid rock if you can because it can be difficult and expensive to remove.
  • Interaction: Even if you never operate on more than one band at a time interaction between antennas is important. The primary ones are damage to inactive receivers and pattern distortion due to mutual coupling. For the SO2R or multi-op contester, or even a fervent DXer simultaneously working two pile-ups, far less interaction can be detrimental.
As you can see there is much to consider. While it is a lot to think through the benefits justify the effort. Why go to all the effort of purchasing a property and then be cavalier planning the placement of towers and antennas? The effort is worth it, even if you cannot achieve an ideal result.
Alternative site plans

Site planning

Even for small stations some advance planning is helpful. It is something I undertook at my previous station when i decided to expand my capabilities. The exercise can pay dividends by avoiding future conflicts and expense. Think carefully about your interests, ambitions and what you might want to tackle in the future.

Draw the layout of your proposed antenna farm, including utilities and adjacent buildings, and even significant distant topographic features.

Alternatively use a satellite view of the area from a service such as Google Maps, as seen above for my property. Import it into one of the many suitable applications that allow you to draw on top of it. I've used Microsoft Powerpoint and Open Office Impress. Precision isn't necessary so these applications are suitable and easy to use.

Initial configuration

Once you stick a shovel in the ground you have made a choice that will constrain your future choices. Choose carefully. I have considered the alternatives and I have put a shovel into the ground. Several shovel, in fact.

The following site plan is the one I am working with. Notice that it is a satellite view of the area around the house with annotations added. I find this approach easier than the alternative of a drawing. Notice that the house is 100 meters the road. Plowing that long driveway in winter will not be fun. Yet this is a great arrangement for antennas because I can maximize the land area within a given radius of the shack.

I'll describe my thoughts on why this configuration is acceptable in the context of my constraints and objectives. The meaning and design of the annotations will also be explained.

The tower annotations are with respect to the physical layout. For self-supporting towers I use a simple yellow circle, for guyed towers the vertices of the triangle are the guy anchors, and for vertical arrays it is the maximum extent or either radials or guys. On both guyed towers I placed a scaled image of a full-size 3 element 40 meter yagi to help with mental imagery.

The scale requires an explanation. Google supplies a scale in the lower right corner. But that is too small to use and it is also inconveniently located. Instead I transformed the scale to the image on my computer screen. I then created several measuring rods in the drawing application that I can paste onto the image, then move and rotate them. You might prefer a more rigourous approach that is not dependent on my screen and application window!

The location of the Trylon self-supporting tower is constrained by the location of the house, septic system, trees and future garage (purple square). This will be first tower to go up, and its construction is underway as of this writing. As previously mentioned, I'm under the gun to get the concrete poured before work on the garage begins. This tower will initially support a large tri-band yagi and 6 meter yagi. It may also be shunt loaded for 80 meters and perhaps 160 until 2017.

The LR20 has been surveyed on the land east of the house as shown on the plan. Excavation is planned for November. I chose the location to minimize visibility from the road, land removed from hay production and distance from the house. Its orientation is not ideal for climbing and, especially, side mounting of yagis. I can work around these minor issues. Over the winter it is unlikely to hold more than inverted vees and a one or two fixed yagi. Next year I plan to raise 40 meter and 20 meter yagis of modest size, or larger if I have the time.

There is provision in the plan for a similar size guyed tower to the south of the house. If I build it one tower will be for 40 and 10 and the other for 20 and 15. This is a common arrangement for contesters since it minimizes interaction among yagis on the same tower by avoiding harmonically related bands and maximizes diversity. If contests are not your passion the need for two tall towers is of less value.

Unfortunately when pointed to Europe the south tower may exacerbate interference with antennas on the east tower. This will have to be addressed with aggressive filtering, and in truth would likely be required in any case.

In the north field I have reserved space for an 80 meter vertical yagi per the design in an earlier article. Alternatively I would put up a 4-square. Spacing from the other towers is sufficient to avoid serious pattern degradation when pointing southeast should any of the towers exhibit a resonance on 80. However there will be no array or even a vertical for 80 and 160 this year.

With respect to noise I have initially avoided placing antennas west of the house. The electrical distribution line is parallel to the road using an easement on my property. If you look closely you'll see the shadows cast by the poles. It is about 70 meters from the house. Antennas would be closer than that.

Notice the placement of measuring sticks to help visualize distances. Then there are the ones further to the east that have a different purpose. These are prospective 100+ meter long Beverages for 80 and 160 reception. Alternatively a 4-square or 8-square circular array could be placed in the wild field to the northeast. Since Beverages are simple and cheap they are more likely to be installed in the near term, and possibly remain my receive antennas of choice.

Receiving antennas are a good choice for the otherwise useless forest and swamp at the eastern extreme of my property. It is not by chance that this area is furthest from power lines and neighbours's houses, and looks towards Europe; it is one of the attractions of the property that caught my eye. I have already been pricing 150 to 200 meter runs of RG6 and control cable. I've also learned to construct small transformers and common mode chokes suitable for 160 and 80 meters.

2017 and beyond

My immediate need is to get towers planted before winter and put up antennas that will get me through the winter and next spring. Starting in 2017 I will begin my long term antenna plan. At this point I don't know how far I'll go, and indeed I prefer to give myself latitude to experiment rather than stick with any fixed ideas.

The site plan must accommodate my particular interests. I believe I've done that. Although now that towers are being planted and their placement constrains my future choices it is beneficial in that I don't have to waste valuable time considering too many possibilities. Or, what we used to called in my business life: analysis paralysis.

My objectives for 2017 include the following, in no particular order:

  • 3-element 40 meter yagi. Which design I will select remains an open question. The antenna will go at the top of the LR20 tower and turned with a prop pitch motor/rotator.
  • Side mount the XM240 2-element 40 meter yagi on the LR20, rotatable with or without a swing arm to cover the US.
  • 80 meter vertical yagi array, including 160 meter vertical.
  • Mono-band yagis for 20 and 15 meters, side mounted on the LR20.
  • Beverage antennas to cover critical directions, primarily for 160 meters but also to supplement the receive directivity of the 80 meter vertical yagi.
  • Tri-band yagis for the Trylon (TH7) and LR20 (TH6, fixed). These are in stock, along with most of the rotators I'll need. One rotatable tri-bander or mono-bander will be mounted above the 40 meter yagi at extreme height.
  • 6 meter yagi on the Trylon.
  • Heliax for all the long runs
Over this winter, once tower and antenna work must cease, I will begin preparatory work on some of these antennas. There is also work to be done building the shack and automation for rig control and antenna switching.

I also have a stretch objective to raise that second guyed tower late in the season. That event depends on many things, and I may not even want it then or ever. But I expect I will do it no later than 2018. Once built the antennas will be rearranged as I described earlier, with one tower for 40 and 10 and the second for 15 and 20. Large yagis for the high bands will be built or purchased for these towers. Progress of the solar cycle will determine priorities.

Antenna experimentation would benefit from an additional small free-standing tower so that the main towers and antennas don't need to be disturbed. However that may be too much for next year. 

Missing the contests

It feels odd to be writing blog posts while the CQ WW SSB contest is underway. In a way all this typing and thinking makes that lack sting a little less. It is also a welcome break from the hard physical labour of digging. I'll have more to say about digging tower holes later.

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