10 GHz EME reception with a 50 cm dish by Hans van Alphen, PA0EHG
In December 2013 a 10 GHz EME beacon DL0SHF was put in operation using an output of 50 watts and a 7.6 meter dish antenna.
The objective of the beacon is to stimulate activity and the provision of a beacon signal via EME for stations who want to experiment.
At first the beacon was a CW beacon beacon that was activated when the moon is visible from Kiel, near Hamburg.
On request there is a possibility that the beacon transmits on really high power.
Then a TWT is used which can provide an output power of 600 Watt.
My first test
In January 2014, I first did a test for receiving the beacon.
With my EME system, a 3 meter dish equipped with auto tracking, I immediately found a good signal from DL0SHF.
3 meter EME dish at PA0EHG
After this initial test I send a mail to DK7LJ (first operator of DL0SHF) and reported my reception and expressed my expectation
that it should be possible to receive the beacon at high power on a dish antenna of 50 cm.
I did not think DK7LJ would respond that fast but almost instantly he offered me to put the beacon direct to high power.
This was a little too quick for me and after some deliberation, I got a half hour of preparation time.
That actually turned out much too short. I had to rush setting up my portable station and connecting it to my receiver.
After the half hour passed I had just turned on the portable station, which still needed to stabilize a while.
Meanwhile, I took a listen to the high power signal on my 3 meter EME antenna and listened
to the huge signal coming in from the beacon with 600 Watt output.
Then I started searching to the beacon signal using my portable system with the 50 cm dish, which was
quite tricky, because aiming a 50 cm Dish on the moon without any visible reference at the moon
and no further antenna position readout is nearly searching for the proverbial needle in a haystack.
My portable station used for first test with a 50 cm dish
After about 5 minutes I found the beacon signal, it was not strong but clearly audible copy listening to the call sign DL0SHF.
In EME report I would give it an M to O report.
Because of the short preparation time I was not using my SDR and I did not take any pictures.
We subsequently agreed that we were going to do the test again with some better preparation on my side.
I the period after my first test, the beacon has been expanded and was able to transmit in digital mode JT64G.
Following a CW transmission, there is also a period of 1 minute with JT64 messages enabling digital modes reception.
Better receive system
After my first success I started to build a dedicated receive system for receiving the 10 GHz beacon DL0SHF.
One of the problems I encountered during my first test was that it was quite hard to get a 50 cm dish aiming at the
moon when the moon is not visible.
Because of my interest in astronomy I found a very nice solution to solve the antenna aligning problem.
At that time there was a nice gearbox for astromical telescopes for sale at reduced price which looked perfect to me to put on my small dish.
Big advantage of this drive is that it already has software in it to calculate moon and sun positions and can automatically track the moon and sun.
In the start the gearbox will need an alignment and can then be calibrated and if this is done accurately from that moment on it is super easy to aim the dish too
the sun or the moon or any other target.
I expect it would also be fine for terrestrial testing because the azimuth readout is really super accurate.
The indication accuracy is reading up to 0.01 degrees, but is likely to be completely mechanically somewhat less accurate.
For targeting a 50 cm dish at 10 GHz with about 4 degrees opening angle that is much better than needed.
For your information, the drive is from IOPTRON and can be sold at your local astronomy store or using google search.
After I installed the dish on the drive and made the whole mechanical construction in balance using a counterweight
I began to assemble and mount the other receiver parts.
The pre-amp is having a very low noise figure of 0.7 dB. As dish feed I am using an aluminium taper from normal
to rectangular waveguide. This is good enough for the optimal illumination of the dish with an F / D of 0.4.
At the back of the dish I mounted the down converter to convert the 10 GHz signal to an IF of 432 MHz.
The IF output is then connected to a FUNcube Dongle on my PC where I can use Spectravue SDR to listen to the signals.
My new receive system 50 cm dish mounted on an IOPTRON gearbox
In late March 2014, I was as ready for my first testing with the new setup.
The first measurements results looked very good. I could measure 3.4 dB solar noise which almost exactly matches the theoretically calculated value.
A few days later the 10 GHz EME beacon would be on high power on request of another ham, so
that was the time for me to see if my new setup could receive the signal.
It worked perfectly, I could copy the CW signal without any problem and also the WSJT signal came
in speaker copy. At that moment I could not yet decode WSJT.
I made SDR recordings and pictures of my experiment. The received signal was reasonable
strong, clearly stronger than when I was using my portable station.
CW signal DL0SHF high power
With the new system I was able to measure a signal to noise ratio of 14 dB at 12 Hz bandwidth.
My experience of the past years at 23 cm with airplane scatter is a signal with a 6 dB S / N ratio is already audible.
If we calculate this to a 3 kHz bandwidth than we get a signal from -18 dB S / N in 3 kHz from which in experience I knew that this can be copied in CW.
CW signal from DL0SHF in high power
JT4G signal from DL0SHF in high power
JT4G decode from DL0SHF in high power
After the initial receipt of DL0SHF using my new system I did some calculations and I came to the conclusion that I actually
should be able to receive the beacon as it is transmitting at low power.
A few days later I had time and the opportunity to listen to DL0SHF in low power.
Unfortunately, that gave me no result at all and I failed that test.
At the same time, however Charlie G3WDG was available for a test.
G3WDG operates with a 3 meter dish and 50 watts output.
He started transmitting a carrier which I found almost immediately on my SDR.
The S / N ratio in 12 Hz was approximately 3 to 4 dB maximum.
The 3 meter EME dish G3WDG
The signal was audible but copying the CW transmission was not poosible and just a small bit too weak.
CW signal G3WDG
Charlie then went on to transmit on JT4F and I recorded these signals using Spectravue.
It all looked good and after some playing with the different settings, I also got excellent decodes of the signal.
It turned out so perfectly possible to receive G3WDG in JT mode using my 50cm dish via EME.
The decoded signal from JT G3WDG
During the 3cm Dubus EME contest I have been listening with this antenna to see if I could receive more stations with my 50 cm dish.
During this test I found the signals from OK1KIR and SP1JLW.
DL0SHF in low power
The improved SSPA of DL0SHF using water-cooling
Because it should be possible to receive DL0SHF in low power I did an
extensively search to find the signal. This was not successful so after this fail I contacted DK7LJ to ask him to check the beacons output.
He replied that the beacon did not have the full 50 Watt output and that is was more than 6 dB lower than intended.
In July, I received the news that the beacon was repaired and actually had been modified substantially.
The 50 Watt SSPA was rebuild and made suitable for water cooling.
The output power had improved to a level of 38 Watt, still sufficient.
I had to wait some time before the position off the moon phase was good to do a test.
In early August I did a test and after adjusting the antenna calibration I could go look for the signal.
That was surely more difficult than expected.
The test I had previously done with G3WDG succeeded quickly but that was
because he started to transmit with a carrier.
The beacon DL0SHF transmits CW but not a long carrier so the averaging in use in the SDR works not as good.
After searching a while I found the very weak signal just visible on my SDR.
In CW, I could very occasionally hear the signal in my headphones but it was definitely too weak to copy.
The CW signal via the SDR
Then I tried to decode the signal JT and after good tuning off the frequency I got good decodes.
JT4G signal from DL0SHF at low power
The decoded signal from JT DL0SHF low power
In September 2014 in France, during the EME conference I held a lecture on receiving DL0SHF with my little dish and I gave a live demonstration of te reception off
DL0SHF at high power.
An overwhelming response made it clear there is very much interest in 10 GHz EME with a small dish.
If we look at the possibilities and experiments I have done is quite obvious that it is possible to make even two-way contacts with this small setup.
Using an output of 50 watts or a bit less QSO's will be possible with multiple stations.
The use of a digital mode as JT65G is required.
At this moment I am working to extend my system with an SSPA (solid state power amplifier) for this.
For more information and to listen to the audio recordings I made, you can take a look at my website www.pa0ehg.com.
On my website are the received audio DL0SHF signals in high power mode and from G3WDG.
Also are there to see the Spectravue images of the various signals.
73 Hans PA0EHG