Stray Signals

FT8 used for ham radio Moonbounce (EME) contact – Southgate Amateur Radio Club

Joe Taylor K1JT reports what is possibly the first FT8 contact via Moonbouce (EME) which took place on Thursday, May 21, 2020 between Paul W2HRO and Peter PA2V

Joe writes:

Paul and Peter used WSJT-X 2.2.0-rc1, a beta-release candidate for version 2.2 of the program WSJT-X.  Both stations have moderate 4-yagi setups on 432.  Conditions today were not particularly good: degradation around 3 dB, and the Sun only 20 degrees from the Moon.

For terrestrial use the FT8 decoder searches over the range -2.5 to +2.4s for clock offset DT between transmitting and receiving stations. 

When “Decode after EME delay” is checked on the WSJT-X “Settings” screen, the accessible DT range becomes -0.5 to +4.4 s.  Just right for EME.

FT8 uses 8-GFSK modulation with tones separated by 6.25 Hz.  At the time of this QSO the expected Doppler spread on the W2HRO – PA2V EME path was 8 Hz, which causes some additional loss of sensitivity.  Nevertheless, as you’ll see in screen shots posted here, copy was solid in both directions:

Why might you want to use FT8 instead of “Old Reliable JT65” for EME QSOs?  FT8 is about 4 dB less sensitive than JT65, but with 15-second T/R sequences it’s four times faster and it doesn’t

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