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Re: poor snr on ao 40 2nd note



Actually this fits my experience as well.
I do not have nearly the receive system Nick has, but when the passband
is on I regularly receive the MB about 8-10dB lower than "predicted"
using the link budgets (specifically Marcus' spreadsheets).  
Signal strength measurements after calibrating my FT-726R S-meter with a
service monitor, and also using a newer spectrum analyzer (w/ additional
preamplification) to monitor MB.
Although the overall signal S/N seems to be OK since I can regularly
make SSB contacts at 62,000km w/o upsetting LEILA (and manually pointed,
at that!).
This is what generated my question earlier in the week about how the S2
TX AGC function works (which was met btw with deafening silence...surely
someone out there knows!).
I have measured my 2' dish system at G/T of -0.4dB which exactly matches
my estimates of 20.9dB gain and Tsys of 135K.  On a 2' dish a pointing
error of 10dB=zero QSOs, not the case.
The only thing I've been able to come up with so far is that the AGC
function is affecting the MB TX power as well, but that doesn't make any
sense architecturally (to me, anyway).


Nick Pugh wrote:
> 
> Helmut
> pointing errors would explain the contradiction in sun noise and lack of
> signal on ao 40 however the dish was manual peaked and made several
> measurements
> 
> nick
> 
> ----- Original Message -----
> From: "Helmut Strickner" <hstr@gil.com.au>
> To: "Nick Pugh" <quadpugh@bellsouth.net>; <amsat-bb@AMSAT.Org>
> Sent: Thursday, September 20, 2001 8:41 AM
> Subject: Re: [amsat-bb] poor snr on ao 40 2nd note
> 
> > I believe that you are having pointing problems with your 6 ft dish!
> >
> > Nick Pugh wrote:
> >
> > > Here is my set up
> > >
> > > 6 ft dish gain 31 db linear pol
> > > DEM pre amp .85 db nf gain 17 db
> > > AIDC 3733 lnb stub removed
> > > 3 db loss coax between LNB and receiver
> > > Yaesu 736 receiver
> > >
> > >
> > > I am receiving 6db of sun noise  this implies g/t of 8 db
> > >
> > > I am receiving the MB  15 db above the noise with squint angle < 10 deg
> > > range app 50 k km.I think that i should see the MB at 27 db above the
> > noise.
> > > To put it another
> > > way if i see 6 db of sun noise what should i see the MB with squint
> angle
> > <
> > > than 10 deg range app 50 k km.
> > >
> >
> >
> > ----
> > Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> > To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
> 
> ----
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----
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