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 possible that the Alphasat is in inclined orbit
Measuring solar noise using my receiver
I tried to measure the solar noise from my RX system
From the past I know the existence of solar outage in receiving geostationary satellite signals.
I tried to calculate the date's for solar outage using an online calculator
Results of these are in the picture below
Using these results I started measuring on 27 february at 10.15 UTC until 10.45 UTC to see if I notice noise increase.
I found at 28 feb a first positive increase but noticed that time was a few
minutes later than predicted in the calculator.
For improving the measured result I place max number of markers each measuring
noise at a different frequency.
Now I show the results of 3 days measurement 28 and 29 February and 1 March.
In the first part of May 2020 I measured the received signal strength during several days.
I already tried to do this measurement much earlier but then I used a tool which was not able to work with the high doppler variation.
For this measurement I use Spectrum lab, the first day I also have some glitches
caused by too large doppler.
This is the measured signal strength from 5 may 09.20 until 8 may 2020 08.44 UTC, it is clearly visible that there is a repetitive pattern
Signal strength is dB signal to noise ratio