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Re: ao-40 downlink question



If that's a standard 18" DBS dish, I'm impressed with its performance.  Are
you using any kind of DSP such as the ClearSpeech or Timewave DSP-599zx?  I
would consider a good DSP (which eliminates most of those which are part of
many transceivers) to be mandatory at those low SNRs.  At least a 3ft. dish
is highly recommended for AO-40's downlink and will, in combination with a
good external DSP, provide "armchair" copy.

73 de Rick, KG6IAL

----- Original Message -----
From: "Bowman, Greg" <Greg.Bowman@icm.siemens.com>
To: "'amsat-bb@amsat.org'" <amsat-bb@AMSAT.Org>
Sent: Tuesday, February 11, 2003 11:25 AM
Subject: [amsat-bb] ao-40 downlink question


> I have assembled an ao-40 2.4ghz downlink setup using a (plastic) direcPC
> dish, a downconverter from K5GNA, and a 6 1/2 turn helix feed (1/2 turn is
> matching) . The receiver is yaesu ft-847 w/2.1khz crystal filter on ssb.
> With the sat at a range of approximately 60,000km the best signal I can
get
> in ssb mode is an S5 with noise floor at S1+  listening to middle
beacon(?)
> or telemetry . CW copied at about S7 with the 500hz filter cut in. SSB
qso's
> are generally readable but not strong, maybe an S3. The helix was tweaked
> using a wiltron site master so I know the helix after mounting has a swr
of
> 1.1:1 at 2401.
>
> My question is, would my receive signal strengths be considered normal for
> the dish, feed, and other equipment I am using? Perhaps someone with a
> similar setup?
>
> Some info I have seen has suggested that the helix be closer to 8 turns to
> match the illumination angle of the dish which I measure to be around 65
> deg. I have also slapped some aluminum foil on the dish which didn't seem
to
> change things either way, varied the distance of the helix from the dish
> center, etc.
>
> Any constructive comments would be appreciated..
>
> Regards,
> N4EN
> ----
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>

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