[Moon-Net] FT8 for EME

F5HRY f5hry at wanadoo.fr
Thu May 21 20:57:51 CEST 2020


When will these computers QSO parties will end ? Certainly never.

What will end is the pleasure that we had to hear signals bounced off 
the Moon. When everybody will have switched to digital, as today on 
144/432 and
partially 1296/2300, only our own echoes will last.

I'm sad.

73,

Hervé F5HRY

“Sooner or later, everything old is new again”
Stephen King (thinking about analog radio modes ...)

Le 21/05/2020 à 20:28, valter dolso via Moon-net a écrit :
> Hi All  :-)
>
>
>
> Very cool indeed ... to think about dismantling my EME setup !!!
> QRV EME since 1988...
> 73, Valter IK1FJI
>
> Il giovedì 21 maggio 2020, 18:41:47 CEST, Mr. Sean McHenry via 
> Moon-net <moon-net at mailman.pe1itr.com> ha scritto:
>
>
> Very cool indeed! Thanks to Joe and the team of testers!
>
> Sean
> KB8JNE
>
> Spell checked by the NSA.
>
>     On Thu, May 21, 2020 at 11:57 AM, Joe Taylor via Moon-net
>     <moon-net at mailman.pe1itr.com> wrote:
>     Hi all Loonies,
>
>     Some here will be interested to learn that earlier today W2HRO and
>     PA2V
>     easily made (as far as I know) the first EME QSO using the FT8 mode.
>
>     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 +2.4
>     s 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
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