Fall Maintenance

It should not be surprising that there is more maintenance for a large station there is for a small one. That means that I have a lot of work ahead of me this fall. I am prioritizing some jobs so that I am ready for the major contests that are rapidly approaching.

Despite all the problems, there are so many antennas that I have been able to continue operating. But that's for casual operating; in a contest I want all of the antennas to be available. That is especially important for multi-op and SO2R where the antennas must be shared among two stations.

In addition to repairs and other maintenance, I have new projects underway or planned. To give you an idea of what's involved to keep my moderately-sized "big gun" station going, I'll show you my to-do list for this fall. First the repairs and then the new projects.

Repairs

20 meter 5-element yagi: The upper rotatable yagi in the 20 meter stack began exhibiting intermittent behaviour in the spring. By midsummer the failure was complete and the antenna became unusable. There is very little that can go wrong in a simple, if large, antenna like this so I knew the repair would be easy. Unfortunately, after testing the entire antenna system in stages, the fault was determined to be at the feed point. It is unreachable from the mast so it had to come down. It is now sitting in the hay field. The repair was indeed simple and I hope to raise it soon. I'll have more to say about the faults and their repair in a future article.

80 meter wire yagi: Deer continue to molest the antenna. One enterprising individual tore apart the "temporary" protection on the southwest parasitic element and proceeding to chew and tug the wires until it pulled off the switch box. When other projects are out of the way I would like to build metal cages for the box and wires, and perhaps replace the bottom 2 meters of the wire element with tubing.

40 meter 3-element yagi: The capacitance hats need to be replaced. It's a complicated job since the antenna is so large and heavy. The replacements have been ready for quite some time. I haven't been in a rush since no more capacitance hat arms have broken and the antenna performs well. I may have to defer this job (again) to next spring.

Side mount rotator: Intermittent operation was found to be a cold solder joint on the Hy-Gain Ham M motor phasing capacitor. I have it mounted on the tower to eliminate loss and eliminate two wires. It currently turns an XM240 40 meter yagi. I had to inspect the capacitor on the tower, determine the fault, bring it down for soldering and then return it to service. Even a simple fix like this takes time due to the climbing. I took the opportunity to replace the enclosure with UV-resistant plastic.

Trees: Half a dozen large dead trees need to be taken down since they threaten Beverage antennas and, in one case, my workshop/garage. Beverages and feed lines will have to be temporarily moved since they're in the fall zone. There are no trees threatening the towers or guys at present, which are mostly well away from the trees. That was by design. Threatening trees are marked with blazes so that they can be identified this winter when all trees have no leaves.

Software: The 160 meter mode of the 80 meter vertical yagi can now be used. This had been a limitation of my antenna selection software that I delayed fixing due to its relative complexity. Along with that, several bugs have been resolved that are related to antennas that are multi-band or on the same port, with an auxiliary switch. Full SO2R and multi-op testing needs to be completed before CQ WW.

Beverages: Ants cut through the taped weep holes of the remote switch so I had to once again evict them. I caught them early so there was no damage. However there is an intermittent in the one or more of the RF paths that occasionally cuts the signal path. Switching appears to be fine. I suspect the RG6 connectors. I will have to open all of them to clean the conductors and ensure that all threads are coated with dielectric grease. Failure of the short east-west Beverage in September was due to the centre conductor of the RG6 breaking off inside the F connector.

Antenna interaction: The side mounted XM240 and TH6 have an interaction on 40 meters that impacts the XM240 when it is pointed approximately west. In that direction it is at right angles to the south pointing TH6. It is not often appreciated that a 3-element yagi has a "hidden" resonance at the next lower band, where it behaves like a short dipole with large capacitance hats (the parasitic elements). I will model the antennas and decide if I can reduce the interaction by raising the TH6 several feet.  It can't go much higher since it'll get too close to the next higher set of guys and the risk of increased interaction with the lower yagi of the 10 meter stack.

160 meters: My failed attempt to broaden the bandwidth of the shunt fed tower with a wire cage for the gamma rod was aggravating. I gave up when the weather got too cold for further attempts, especially as contests approached and the 160 meter season was well underway. I will try again this month once the 20 meter yagi is back on the tower. I don't roll out the radials while I have ground crew helping me with tower work since they are a safety risk. Breaks in the radials due to critters must also be mended -- wire nuts served as temporary repairs.

Prop pitch motor controller: There was no lightning damage this year but I diagnosed and repaired damage from last year. The motors turned slowly and the current draw was high. One motor was affected more than the other so I suspected a motor problem. The motors are fine. I mistakenly relied on the current measurement when I ought to have measured the voltage. The old controller I am currently using (it will be replaced) only produces 24 VDC under no load. Under load that drops 2 or 3 volts even with a large filter capacitor, and is lower still at the motor due to wire resistance. When I measured it this summer it was between 17 and 19 volts at the power supply. I discovered that the bridge rectifier was damaged by lightning. Semiconductor devices can partially fail when they are hit by a voltage spike. A new 50 amp bridge rectifier fixed the power supply. I ordered several; they're inexpensive.

New projects

Although repairs receive the highest priority, this station is constantly changing and growing. The changes are mostly incremental now that the station is mature. This is a list of new projects that I am working on. Most won't be completed this winter, but all are being worked on as time allows.

40 meter reversible Moxon: Mechanical construction is mostly complete. The half elements are too long to keep in the workshop so they've been moved outside along with the boom. Dimensions and component values have been fine tuned using NEC5. The elements are not yet mounted onto the boom and the switching system isn't built. With luck it'll go up in late fall.

Stubs: Although a simple addition to the station, I have yet to do it. This is a job that is easy to do during winter so I have deferred it. I really should have done it last winter. The easiest stubs are for 80 and 40 meters, to suppress harmonics on the second and third harmonics, because the antennas for those bands are connected to their own auxiliary switches instead of separate ports on the 2×8 switch.

Antenna selection software: The UI (user interface) has not stood the test of time. Operators select the wrong antenna, don't know which are available and, for SO2R and multi-op, one UI is difficult to use and confusing. Design for its replacement is well advanced, although development has yet to begin. It will feature separate UI windows for each station, which can be networked on different computers, and limit the display to the availability of the antennas for only the current band, including receive antennas. I plan to write the software over the winter. The Arduino switching system does not need to change, although I'd like to migrate PC communication form USB to wireless.

80 meter wire yagi: There are several electrical and mechanical improvements on my list. I've been deferring them as the solar maximum has waxed since 80 is less important than the high bands for the time being. I intend to add SSB yagi modes (it is currently only a yagi on CW), install concrete bases, replace the tower with a taller one (to remove the troublesome stinger), decrease ground loss, improve critter protection (see above), and a few other changes. I will do what I can this fall and winter as the weather and other projects allow. Most will wait until at least 2025.

New prop pitch motor controller: I am well along in the construction of an Arduino-based controller for the two prop pitch motor rotators. The first step is direction indication, followed later by rotation controls. The project has been idle for several months due to lack of time and some confusion over non-linearity in the op amp circuits. Eventually I will interface it to a PC for software control. An article will follow once the controller is complete.

6 meter Moxon: The Moxon is on the small tower bracketed to the house. There is no rotator or coax! I haven't yet decided how to proceed, whether to fix the direction or make it rotatable. My objective is rapid propagation checks in different directions.

Small is beautiful?

It should be obvious that a big station is not for everyone! There's always work to do so it has to be something you enjoy. I do, most hams do not and I can't fault them. Dreaming of a big station is far less stressful than owning one!

Between good DX conditions on 6 meters, DXpeditions and station maintenance, fall is a busy time. We've had unexpectedly mild weather which is very welcome to getting the work done. However, good weather is good for other outdoor activities competing for my time. Somehow I have to do both.