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.
||Tap 1 to …
|80 m||–||128.0 cm||15.5 m|
|40 m||2||128.0 cm||7.8 m|
|30 m||2||51.5 cm||5.4 m|
|20 m||3||128.0 cm||3.9 m|
|17 m||3||82.5 cm||3.0 m|
|15 m||4||128.0 cm||2.6 m|
|12 m||4||100.0 cm||2.2 m|
|10 m||5||128.0 cm||1.9 m|
|6 m||6||106.5 cm||1.4 m|
|2 m||6||120.5 cm||none|
Note: On the 2 meter band it is not necessary with a radial, since the chasis can provide enough counterpoise. On this band the antenna will work as an 5/8 lambda GP.
I am still experiimenting so the table below is not quite complete yet. The Width is the frequency range where SWR stays below 1.5.
|80 m||121 cm||7.8 m||7.020 MHz||40 kHz|
|30 m||35.5 cm||5.4 m||10.125 MHz||50+ kHz|
|20 m||128 cm||3.9 m||14.030 MHz||300+ kHz|
So far, I have only used the suggested values. I will do some experiments later.