Echoes Of Apollo [EofA] is an Amateur Radio event remembering 40 years on of the space missions to the moon and a small team of us designed, assembled, tested and operated a temporary station to participate.
Amateurs, usually known by first name and callsign (ZL2TV for our station), will transmit as powerful beam as available from their earth station to the surface of the moon whence it becomes scattered in the reverse to be received back on earth approximately 2.5 seconds later. The art is known as EME, for Earth-Moon-Earth, or simply moonbounce.
In 2009, when the inaugural EofA project to activate as many large Apollo-era dishes for a day of Moon talk was announced, I had good reason to be interested. My workplace had one remaining 30.5 metre, fully steerable antenna that had been replaced with a smaller model and the site decommissioned, a fate already dealt to five similar size dishes and countless 10-metre class TVRO setups around the country.
Permissions were obtained and I had 3 weeks to plan the technical aspects of making it work on the 1296MHz frequency. Planning included the possibility of involvement with Scouting groups etc. to fully participate in EofA and the other big dishes that would be active on this weekend event. This is a beam waveguide-fed Cassegrain dish and the feed comprises of a corrugated horn of 0.85m diameter. I constructed a dual probe, cylindrical feed with 90 degree hybrid coupler, whilst Steve ZL1TPH constructed a round septum feed. The plan was to try both and go with one that worked, as the exact size of the hole in the horn could not be determined till the day.
Then a problem occurred requiring the old dish for service and we had to sit that one out for a year. Constructed equipment was quarrantined and plans were kept till the day came, about 2 days prior of the 2010 EofA event, that word came "go for launch".
Again there was no opportunity to pre-test any systems. Harry ZL1BK arrived to help with the final installation and keep the moon in our sights for the duration. The moon was already up but, our Saturday being early for most other stations (12 hrs ahead of UTC), we weren’t in a hurry. Sun noise was checked and less than anticipated …. final calibration suggests 12db was received. After connecting a Spectran monitor laptop to the audio, echoes were identified and then heard on the speaker, as tuning and tracking were established. Opportunity was taken to measure the sun -3dB beam width when slewing the elevation. This occurred at 0.6 degrees, suggesting 0.2 degrees beam width in the antenna, something I expected as a consequence of illuminating the sub reflector from the same area of horn aperture designed for 4GHz. In effect, we were lowering the gain by limiting the field of view on 23cm to that provided on 3.7GHz, spilling the rest of the beam out to cold sky and/or the walls of the beam waveguide system and its 4 periscope mirrors and tube.
As far as possible, in keeping with EofA, 1970s equipment was used ... a Microwave Modules Ltd. converter, an Icom IC202s modified with Quindar tones The LNA and SSPA (amplifiers) were somewhat more modern Mini-Kits from Australia and a 60 watts output combined pair of Aprisa TX boards from 4RF New Zealand.
EofA 2010 included the Arecibo dish on the 144MHz frequency and activity seemed to have moved from the original theme of "talk via the moon" on 1296MHz, so the challenge was to upscale to a band we could talk via the moon, such as the 5760MHz European activity session the following weekend. A homebrew transverter as normally used for local terrestrial operating, Icom IC706 exciter (to accomodate the large doppler shifts) and modified feed launcher were fitted up to the corrugated horn and testing showed cw (morse) echoes were possible down to 50 milliwatts power. Tests were also carried out , ssb and FM, and to TED ZL2IP in Inglewood direct. Own echoes on ssb at the highest power of 275 watts returned an etheral clarity which was quite unexpected both to ourselves and participating stations.
This size dish is not optimal for EME and was a two - person operation keeping it on track while operating via the moon, an unforgettable experience especially for us EME rookies at 3am on a misty night! The VK3UM Australian EME software deserves special mention it provides a lot of pre-planning, necessary as the Moon waits for no-one. It was pleasing to be able to put the antenna, which I was involved in building and testing during 1984, through some new paces - or should I say frontiers, before it wanders into the twilight zone.
Moonbase Alpha team - Ralph ZL2TV, Steve ZL1TPH, Harry ZL1BK, Colin ZL1BTT 5 GHz Ranging station - Ted ZL2IP QSL Manager - John ZL4JY
