[amsat-bb] Re: ARISSat-1 over West Malaysia

Phil Karn karn at philkarn.net
Fri Aug 5 10:28:23 PDT 2011

On 8/4/11 8:04 PM, Sion Chow Q. C. (9W2QC) wrote:
> 2. Does the CW beacon needs to be really +/- 100 Hz of the yellow  
> line?  The reason for this is that I would like to see how much offset  
> should I apply to doppler control, for possible automated reception.

Tuning the CW beacon to 500 Hz automatically centers the BPSK1000 signal
at 1500 Hz. I didn't put in a whole lot of frequency tolerance in the
BPSK-1000 demodulator because the signal is 2 kHz wide from null to null
and it would begin to be chopped off by the edges of the receiver's SSB
filter. So while you should ideally tune to +/- 100 Hz you might go to
+/- 200 or even 300 Hz and it will *probably* still work, but I wouldn't
go too much wider.

Go ahead and experiment; I'd be interested in any reports on how well my
demodulator (which is incorporated into both the Windows and Mac
telemetry programs) tolerates tuning errors. Frequency acquisition and
data synchronization are the hardest parts of any digital demodulator,
and I'd like to know where there's room for improvement.

73, Phil

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