Receiving the Alphasat Beacon on 39 GHz
After interest in millimetre wave EME is tried to receive the Q-band beacon from Alphasat at 39.402 GHz
Some data from the available beacons
My initial idea to try and receive the beacon was to use a Witlink 2000 microwave link receiver and test to receive the beacon.
I tried a setup able to receive between 38.7 and 39.5 GHz so quite usable for this experiment.
After connecting the Witlink 2000 to power supply I found that
the unit had an output at 141 MHz but this was only 5 MHz wide.
After this fail I tried to disconnect the first down converter and see at what IF the expected frequency would be, a measurement using the harmonics of my 18 GHz synthesizer learned me that the IF for receiving the Alphasat beacon would be around 3410 MHz. So that was easy and I became the idea that for the time being the best way to proceed is using a available converter for 9 cm to 2 meter to get an IF of 154 MHz.
An initial test with the 18 GHz synthesizer worked out fine and I could receive the frequency of the beacon. Some more mechanical preparation was done and then I had to wait for some good weather to try life receive of Alphasat.
On 5 February 2020 weather was nice and I mounted the Witlink unit on my mast.
For receiving Alphasat I need an elevation of 27.5 degrees and an azimuth of 157.8 degrees.
With help of some nice app's on my Iphone I adjusted the dish as good as possible to the needed heading and I tried to find a signal using a spectrum analyzer, but nothing was found.
I then started turning the dish up and down and later right and left and after about 15 minutes I found a signal.
Optimalisation of azimuth and elevation took me lot longer
The receive system is the standard Witlink front end so a lot of extra losses between antenna and the pre amp.
Perhaps I will rebuild a unit special for receiving Alphasat and make some long term measurements of received signal strength
Interesting measurement result: 20-2-2020
During the monitoring of the Alphasat beacon I found that the received frequency
was having quite some doppler on it
I measured the received signal for a few days and it is obvious that the orbit is a daily repetitive pattern
I measured this using SBSpectrum, there is some ripple on the measured
It is obvious that around 3 hr and 15 hr the orbit is returning, the satellite drifts a eight form orbit through hemisphere every day
The scale of this measurement: the vertical scale is in total 4800 Hz wide
In total I measured 4266 Hz doppler
this is much more than published and therefore it's obvious that the Alphasat is in inclined orbit due to end of life period of the satellite