AO-40 mode-S (in 2001)


I decided to build a helical antenna for my first tests on 13cm. The 19-turn helix with a downconverter "MKU-24"
by DB6NT gives a good performance in receiving the telemetrie. I was able to work on the S2-transponder at >60000km!
Of course, the signals were weak, but most of them are readable.


The main problem is, that I live downstairs. The vhf/uhf antennas are all under the roof, but on 2,4GHz the results must be
close to zero. So I have to test it (and work with it !) in front of my window!


After 2 month with the helical, I got a (low cost) 60cm dish (f/D=0,4) from "UKW-Berichte", and the surplus gave me a
cheap tripoid. So some mechanical work has to be done...


After several hours the dish was ready for the first test . The converter (in a weatherproof and isulated box) is directly
connected to the feeder (2,5 turns). The antenna can be dismounted with just 4 srews !


close view to the feeder

feeder dimensions of the feeder complete dish on tripoid

Here the view to the "ready for test" dish. After several tests it seems that the dish is about 10db better in s/n than
the 19-turn helix! The difference is nearly the same as between S2 and S1 transponder of AO-40. Obviously the systemnoice
is very low compared to the helix.


73 de Michael