Sunday, November 20, 2011


This weekend was one of the ARRL EME (Earth-Moon-Earth) contests, and I spent quite a bit of time listening for signals reflected from the moon. The signals I was listening to were JT65b type, which is a coded series of tones; WSJT software can encode and decode these tones, translating them to and from text on a computer screen. After hearing a number of particularly loud stations, I was able to make an EME contact, yay!!

The following screen shows the spectrogram of K5GW's (Texas) signal reflected from the moon a few minutes before the contact:

And the next screen shows the WSJT software on my computer after decoding K5GW's reply to me.

At first I didn't believe that the decode was real, but shortly thereafter a ham at Stanford sent me an email saying he heard the reply too:

112 -89 0 1602 3.0 -12 KB5WIA K5GW EM13 OOO 1 0

The numbers above indicate that at 1602 UTC, the Stanford station heard a signal coming from K5GW with a 3.0 second time delay (it takes 2.6 seconds for a signal to get to the moon and come back, plus a fraction of a second of clock error). The -12 indicates the relative signal to noise ratio (a very strong signal). KB5WIA is my call sign, the EM13 is K5GW's grid locator, and the OOO is a shorthand for "I've heard your signal reflected from the moon and I'm replying to you". The 1 after the OOO's indicates that the WSJT software has decoded all of this information successfully with no errors.

The power I used was 30 watts (a Yaesu FT-817ND running at 2.5 watts into an RFConcepts 2 to 30 watt linear amplifier), essentially the VHF part of my normal satellite station:

The antenna was the same M2 2M7 seven element 2 meter yagi that I normally use for satellite uplink and downlink:

All in all, pretty exciting to have ham radio signals travel 250,000 miles to the moon, bounce off the rocks and dust up there, and then travel 250,000 miles back to earth and be picked up!!!!

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