Wednesday, 28 March 2018

Moonbounce - another milestone passed!

Warning: This blog post looks to be shamelessly self-congratulatory.

My first Earth-Moon-Earth contact at last!
144MHz EME QSOs on 27 March 2018 on dxMaps
After doing my usual drill of watching the moon charts and the chat boards, in particular this one:-

... and tuning to every likely frequency, I finally heard a good strong station - Dimtrij, UA3TPW.

He was busy with somebody else so I posted on the cluster that I was hearing him (though I doubt that doing that made much difference). Then I sat and waited for about 10 minutes until the chat indicated that the other station had given up.

I cranked up the Gemini 2 linear to full output and called UA3TPW. Much to my surprise he came back with my callsign and OOO, indicating that he was ready for my confirmation. So I sent the shortcut "RO" in the approved manner to indicate that I had received his signal and to send my own confirmation. To my surprise back came the shortcut RRR, so that was that. Technically, QSO complete.

I got a bit excited at this point and I sent RO one more time and got RRR again. Then I sent both callsigns and 73, intending to make certain that the whole thing was not a mistake and he hadn't been working someone else down the street. It looked genuine enough as the frequency was the same but you do know about my paranoia. But sure enough he returned with both callsigns and 73.
WSJT-X reception at GM4FVM. The repetition of UA3TPW's previous message is an artifact
To be even more certain I went over to the chat site to find that he had acknowledged the QSO there too!
Extract from JT65 EME chat site
Thanks Dimtrij!

To say that I am amazed about that contact would be a fairly major understatement. I did call a station the day before but it came to nothing as I had rather expected. As a complete rookie at this I thought it would take some time to get right.

The surface distance to UA3TPW is 2561km, though the route the radio signals took is more or less twice the GM4FVM-Moon-GM4FVM distance (approx 2 x 369600 = 739200km on 27 March 2018). Give or take a few km for the Moon to Russia distance of course.

I had read in the books that modest stations like mine, with a single horizontal yagi and conventional gear running less than the full legal power can indeed work via Earth-Moon-Earth. I just imagined that this possibility did not apply to me.

By some odd co-incidence David GM4JJJ was looking at the same station and produced this screenshot of the whole thing:-
GM4JJJ's screenshot.
I do realise that this is not such a dramatic thing; after all lots of people use Earth-Moon-Earth communication. I also know that the steady improvement I have been making to my 144 MHz station would bring it about some time. However, I am still rather amazed by it actually happening.

Thanks to both Bri, G0MJI and David GM4JJJ. They have both been very helpful during this process and they had a lot to do with this first EME contact. It certainly would not have been possible without Joe Taylor and the WSJT-X team - not with my CW anyway. On the hardware side I have the improved lots of things in the station. The main thing that broke to logjam, in my opinion, was my new SPID rotator. If you cannot point your antenna accurately at the Moon you haven't a hope.

GM4JJJ also sent me this link to W7GJ's hints for working EME with JT65. I found it very useful and I brought my EME configuration of WSJT-X into line with it before having the first QSO:-

More details on the various station improvements here will follow once they are complete.

This is not quite a "Volga Boatman" moment. It was a bit too technical and it had been in the "vague planning" stage for weeks. However, it reminds me of 5 February 1975 and my first VHF QSO which was with G8IMU. This was across south London, maybe 20km. I can assure you that at the time I was not thinking of Earth-Moon-Earth.

Anyone out there thinking about trying Earth-Moon-Earth? I would encourage them to give it a go, but it does get a bit overwhelming when it actually works for the first time.





  1. Congratulations Jim!

    I was privileged to witness this historic EME contact. You managed to remain calm enough to send callsign with your 73 message. It’s not easy to appreciate the huge pleasure you get from your very first EME, truly a momentous event for anyone.

    Comparing your dB reports to mine, shows you were getting better results. I was using the transverter with my FunCUBE on the I.F. into MAP65 so that I could get a wideband view of the band at the time. My antenna was at a different height above ground to yours, so the vertical pattern of peaks and nulls would be different, possibly accounting for the differences. There again, it is just as likely that all the work with masthead preamp and better feeder really has paid off at GM4FVM.

    Well done Jim!

  2. My comment about the reported signal to noise being better at Jim's receiver to mine can be explained that in the case of messages sent to Jim, the deep search decoder would give about 4dB of Extra S/N for Jim but not for me (unless I changed my callsign to GM4FVM) I could actually try that as I retained the wideband IQ recordings and can replay them. You will note that the RRR messages were much closer in S/N for us both, as they do not benefit from Deep Search by either of us. For further details read the WSJT manual by K1JT, as I should have before posting!

  3. David
    I think I have mis-understood Deep Search too. I was under the impression it produced a result as if there was a 4dB improvement in S/N. I did not think that the difference actually showed in the S/N figure. I have read all this again but I am no wiser.
    I also wondered about the Doppler shift. I presume you were hearing me direct whereas you were hearing UA3TPW via the E-M-E path so that there would have been more difference in our rx frequencies at your end.
    On the other hand I think that I should just accept all this and do some more work before I return to show how little I actually know about it. We are amateurs, and I am willing to learn even if it takes ages.
    Thanks again for all your help and encouragement.
    73 Jim GM4FVM