Having set up and calibrated the magnetic loop antenna that I bought at Friedrichshafen (details to be added under equipment/antennas at some point). It was time to try it out for real on a summit rather than just on the antenna analyser or on the balcony. So equipped with a piece of equipment that hopefully later I wont need to take with me (a table). The now standard Xiegu X-108G, with its sunshade (not that it was needed), battery box and other accessories along with the disassembled “DL4KCJ Direct gamma match fed asymmetrical magnetic loop antenna” were packed for the outing. I planned to try to make contacts on 80m (which hasn’t been done from this summit before), 40m and 20m. It would be interesting to put up the normal dipole as well to compare the antennas but I decided just to concentrate on the loop.
Rentschen is a one point, flat summit which lends itself well to antenna tests as there is a lot of space with no obstructions. It is about a 50 minutes drive from my home and therefore one of my “local” summits. The actual summit is marked by a trig-point stone which is about 100m away from the road, where I would park my car as usual. The summit is between Rottenbuch and Steingaden villages.
I have driven the route down many times so I did not need my GPS navi or maps. About 15 minutes into the drive a few spots of rain fell and then it stopped. Some rain was forecast but hopefully there would also be some dry intervals, so I kept on driving. Soon the rain was back and as time went on, it got heavier and heavier. It never got to storm level but by the time I arrived at the summit it was a constant soaking drizzle. In fact it continued this way for the rest of the day.
OK so after driving down, I wasn’t going to turn around without at least trying some tests. I didn’t need 4 contacts as I had already activated the summit in 2018, so I would get no points for it, but a few contacts would be nice.
I started on 80m with the antenna set as I had calibrated it at home, SWR looked good tuning around I could hear a couple of stations fairly well, so I chose a free frequency, spotted myself and started calling CQ. Nothing! I called for over 10 minutes without one response. OK I thought, there simply aren’t that many chasers on 80m, I will try the more usual band, 40m. After adjusting the antenna to my settings for 40m, I could see there was something wrong straight away as the SWR was so high that the rig refused to transmit. I played around with the antenna settings, the location of the gamma match and the setting of the variable capacitor, but could not make any improvement to the SWR. It had tested OK at home, so this was a strange problem. In any case, I didn’t want to spend more time in the rain than I must, so I switched to 20m, adjusted the antenna again and this time the SWR was under 2:1 so I spotted myself and called CQ SOTA with the reward of three contacts. 20m was strange though, with a high noise level plus very deep QSB, with the result that stations I would normally be able to work without trouble, I was having to really listen to hear their reports. Not ideal conditions to test an antenna in!
By this time I had, had enough of the rain. I had proved that the antenna works on 20m albeit not brilliantly, I think 80m is fine but 40m would need more investigation. Why do the settings work from home on the other bands but not 40m? I will definitely need to do some further portable tests with the antenna, perhaps not another SOTA summit until I understand better how to tune the antenna.
For now I was happy to get back into the car and drive home.
DL4KCJ Magnetic Loop antenna.
Thick plastic painters sheet
Mini-VSWR meter and coax cables.
The loop needs to be checked on 40m again, first at home and then at some portable location. – Later tests showed that my Rig Expert AA-30 Antenna Analyser was no longer accurate. It was indicating the wrong frequency for the resonance of the antenna. Strangely – when used attached to a PC, the PC software shows the correct frequency, so I have now re-calibrated the loop using the PC program through the analyser. As yet Rig Expert have been unable to find the reason for this fault in their equipment when used stand-alone.
The mini-VSWR bridge I had with me was not good for some bands as in cal. it wouldn’t go all the way across. However the SWR scan feature in the rig – while rather wide on it’s frequency range does appear to be accurate.
73 ’til the next Summit!