ARLA/CLUSTER: Modo digital FT8 usado em contactos de rebote lunar (EME)

[João Costa > CT1FBF]

FT8 used for ham radio Moonbounce (EME) contact

*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:

https://physics.princeton.edu/pulsar/k1jt/W2HRO_PA2V_432_EME_1.jpg
https://physics.princeton.edu/pulsar/k1jt/W2HRO_PA2V_432_EME_2.jpg

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 use Deep Search.

When I was active in EME contests on 144 MHz, I was always frustrated that
even with reasonably strong (for EME) signals, one's maximum JT65 QSO rate
is about 12 per hour.  With FT8 you can do 40 per hour, as long as workable
stations are available.

What about FT8 EME on 1296 MHz?  It might sometimes work, but Doppler
spread will probably make standard FT8 a problem.  But if there were
sufficient interest, we could make an "FT8B" or "FT8C" with wider tone
spacing.

Please try FT8 for EME on any of the bands 144, 432, and 1296 MHz, and let
us know your results.

*73, Joe, K1JT*

The popular WSJT-X software for FT8 can be downloaded from
https://physics.princeton.edu/pulsar/k1jt/

Moon-Net Email Reflector
http://mailman.pe1itr.com/mailman/listinfo/moon-net
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