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Re: AO-51 S-band downlink on mode L/S always on?



The S band downlink is not PTT'ed with the PL tone, so while we are in this mode, the transmitter is on 24/7. There may not always be any audio on the downlink, but the signal will always be there (either a carrier, or repeated static). Try disabling the AGC on the 817. Mine acts funny with a big signal like you get out of a downconverter. A 6 to 10 db tv style attenuator in the coax might be a good idea to bring that IF signal down some, and maybe keep from frying the downconverter if you accidently transmit into it.

Take a look at the article in the last Journal on operating V/S. Most of the information there about reception carries over to L/S as well.

73, Drew KO4MA

-----Original Message-----
From: Bruce Robertson <broberts@mta.ca>
Sent: Oct 24, 2005 3:31 PM
To: amsat-bb@amsat.org
Subject: [amsat-bb] AO-51 S-band downlink on mode L/S always on?

I'm planning on trying out my CalAmp 6-buck modified downconverter on AO-51
within the next 24h. I've tested this unit only with the aid of a 40MHz computer
oscillator doing its thing on the 60th harmonic. This tends to be pretty wobbly,
and not exactly on 2.4 gig, so I'll have to hunt for the downlink as it dopplers
itself across the band. I have made a small patch antenna which appears to
provide considerable gain and exhibits the proper directionality. However, I've
been unable to use my FT-817's S-meter to peak the comb filter in any sort of
proper manner. I'm worried that my unit might be deafened by that.

The only way to find out is to listen to AO-51. On the 435 MHz downlink, I find
that AO-51 is always transmitting an FM carrier, making it quite easy to find.
Should I expect the same on S-band? Or will the relative lack of L-band uplinks
mean that occasionally the S-band transmitter goes silent? I'm trying to
determine ahead of time if a negative result is significant.

73, VE9QRP
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