The resonnance frequency of the ATX-1080 is adjusted by selecting the correct taps to connect (band change) and adjusting the telescope length for fine tuning on the given frequency. The radial length should have different lengths for each band as well. The original document describes which taps need to be connected and how long the telescope should be on each band, but says only that the radial length should be less than 1/4 lambda. Wimo, on the other hand, provides to pages of documentation in German, where they also give some start lengths for the radials. Also, a useful formula l [m] = 54 / f [MHz] is provided.
The ATX-1080 is a small multi band vertical antenna covering 80 – 6 meters, including the WARC bands. It is very similar to the MP-1, a major difference being that the coil is placed at the bottom. Also, the MP-1 has a continuous tuning on the coil while the ATX-1080 has fixed taps for the connections. I bought the antenna at the German Wimo who even supplies some extra documentation along with the original paper.
During my indoor tests of the ATX-1080 tonight I tried to switch to 80 meters.
I am trying again on 40 meters with the ATX indoors. It seems to make a big difference whether the radial is just thrown down on the floor or it is deployed to its full length. In the latter case SWR comes down to 1.1 or “1 bar” on the FT-817, which is somehow better than what I had outside, while in the first case I just couldn’t get the SWR below “4 bars”.
The weather was quite rainy today but it cleared up during the afternoon. I decided to go outside with the FT-817 and the ATX-1080 antenna to make some SWR measurements. I also wanted to se how reliable the built-in SWR meter of the FT-187 actually is.