‘Armstrong’ Antenna Rotator and Doppler Tuning by Ear for Space Station!

Veteran amateur radio operator VU2VK who celebrated his ninetieth birthday recently used to mention in the era of homebrew radios that ‘S Meter is in our Ears’, as our homebrew radios seldom had an S meter! I was in the habit of Doppler tuning for LEO satellite operations by viewing the display of Argentinian Amsat Satellite pass page in one mobile phone and recording the pass in another mobile phone. One of my mobile phones went QRT and I was stuck with just one mobile phone and I was wondering what to do.

I took a printout of the satellite pass direction and decided to manually rotate the antenna, with initial position a little beyond the beginning of the pass and by about middle of the pass to a direction almost perpendicular to that so that it can pick up signals beyond the time of closest approach. That is a new method which I had adopted recently to cover most of the pass with my Moxon Yagi which has a beam width of about 120 degrees on VHF and 80 degrees on UHF. Agreed, this is nowhere near a direct antenna pointing from outdoors in both azimuth and elevation as most of the excellent LEO satellite operators do.

I used the other mobile phone to record the pass, which has been a video recording for the past few passes instead of the audio only recording which I used to do earlier. I tried Doppler tuning just as we used to tune shortwave radios long back listening to the signal, especially the weaker stations which had a lot of QSB. In those days when we had no knowledge of radio propagation, elders in the region used to say that the signal strength is varying by the wind, with signals become stronger when it is blowing towards you from the station and waning when the wind is blowing away from you! But in case of LEO satellites, you need to know the nominal frequency and approximate direction and increment of change as the satellite moves from one horizon to another horizon. The clock in the room and the printout also gave some guidance. Here is a video recording of the pass from the time I could hear signals from the space station to the time when I lost the signals. Hissing noise is the noise of open squelch in the radio, which closes when signals are acquired.