Moon Bounce on 15M

VK3YNV

Moderator
This was one of the more memorable events of the weekend. Very few people in history have managed to bounce signals on the HF bands off the moon, and only very few amateur stations have succeeded on 15 meters.

This thread is the place to tell the story of the planning, and research that preceeded the 15M EME experiments. Over the next few days I'll post as much as I can find by way of pictures, video and documentation.

First echoes were detected around midnight Friday. -- Photo by Lee VK3GK
6.png

The possibility of using the RA Antenna systems for EME was first raised by Rod VK3UG at one of the VI3RA
planning meetings, and referred to earlier CSIRO experiments in the 1950's, so that was a good place to start researching.

The experimental results were published in the IRE Proceedings March 1951, ( IRE == Institute of Radio Engineers )
The 1951 IRE paper and experimental setup are described here.. https://ra.sadarc.org/#!/histeme

More to come... Where is moonrise going to be on the dates concerned? And is there an array pointing in the right direction that
is usable on the frequency concerned?
 
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VK3YNV

Moderator
Josh worked out the moonrise / moonset azimuth directions on the dates around the weekend

Friday 13th Moonrise 105 az @ 22:15 13/3/2020 -- Azimuth at Elevation of 15 degrees is 94 at 23:24
Saturday 14th Moonset 260az @ 10:53 14/3/2020
Saturday 14th Moonrise 111az @ 22:52 14/3/2020 -- Azimuth at Elevation of 15 degrees is 100 at 00:15
Sunday 15th Moonset 245az @13:13 15/3/2020
Sunday 15th Moonrise 115az @23:30 15/3/2020

So the best times would appear to be Friday and Saturday Night, time to see if there is a suitable array.

Turns out that PX5 looks promising. It could be slewed +-30 degrees by using the slew switches to point to 100 degrees and has a nice flat response on 15M


AzimuthalMapPX5.jpg

On the Friday night, of the event, the moonrise azimuth is 105 degrees and as it rises it moves directly through the boresight of PX5. Further it is still within the main beam by the time it rises to 15 degrees elevation just before midnight. So far so good.

With that in mind the DX engineering 1KW Balun and the LDF 5-50 coax was reserved for installation on PX5.

There was some discussion about F2 layer reflections, but seeing as we are in a sunspot low, and the moonrise times are late at night it was felt that we had a good chance. Nigel sent an email with the space weather report for the weekend, and checking the MUF (maximum usable frequency) predictions and the MUF was less than 10 Mhz, But it was strange in a way, hoping for poor propagation conditions so that our 21 Mhz signals would sail right through the F2 layer and not be bounced back to earth. It's not normal for Amateurs to be hoping for poor propagation.

As the signal travels through the upper atmosphere and ionosphere, especially at low angles close to the horizon, the signal tends to bend downwards beyond the horizon, so it's possible that we could get echoes from the moon even before the official moon rise times.

The other consideration is the exact characteristics of PX5, what's the takeoff angle and gain?

We aready knew the boresight was 40/70/100 slew 30. Further searching of the archives found the gain on 21 Mhz was 23.8 dBi and a beam width of 10 degrees, the plots that Josh did, reflect the 10 degree beam width, which it was assumed to be the 3db point in the pattern.
( Someone correct me if I got that wrong )

So we have 23.8 dB of gain pointing at 95-105 degrees azimuth at a moonrise azimuth starting at 105 degrees and moving into the beam as it rises, and we also have promising propagation conditions.

Next installment to come.... the equipment.
 
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VK3YNV

Moderator
The equipment setup was the ICOM 7610 with SPE Expert 1.5K-FA Linear Amplifier, Audio was fed to a laptop running WSJT-X software, but for the test we were transmitting pure tone bursts, not encoded. Although we did try sending a few tentative CQ's on the Saturday Night.

Rex VK3OF set up the ICOM 7610 and narrowed down the audio bandwidth to just a few Hz.

EME_Setup.png

The operating precedure was to transmit a short tone burst and wait to see if we could see anything on the waterfall.

For the first 10-15 minutes we got nothing, and then Rex started to see echoes... So we all crowded around straining to see faint white blips
on the waterfall, as time went on and the moon rose higher the blips became easier to see, and were delayed by a couple of seconds from the
transmit tone bursts. The round trip time for a radio signal to travel to the moon and back is about 2.5 seconds, so the fact that the blips were delayed by the right amount was a clear indication that we were really seeing echoes from the moon.

EME_blips.png


As the moon rose higher and out of the beam of PX5 the blips slowly faded away and everyone declared the experiment a success.

The success was due to the hard work and planning of many, but especially Rex VK3OF, Rod VK3UG, Josh, and many others who contributed.

It was great to be there and witness a little bit of history, no doubt people will talk in years to come of the time that Radio Amateurs with low power equipment bounced signals off the moon on 21 Mhz.

Ray
VK3YNV
 

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