[amsat-bb] Re: Dumb question 9600 FSK

David W0DHB dave at w0dhb.net
Fri Nov 22 07:32:59 PST 2013

Thanks Gordon and others.

Is there any SDR software that supports the FCDP and will demod FM properly
for 9.6K FSK ?


-----Original Message-----
From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
Behalf Of Gordon JC Pearce
Sent: Friday, November 22, 2013 2:36 AM
To: amsat-bb at amsat.org
Subject: [amsat-bb] Re: Dumb question 9600 FSK

On Thu, Nov 21, 2013 at 03:45:04PM -0700, David W0DHB wrote:
> What mode should your RX be in to receive the 9600 baud FSK telemetry
> downlink signals. USB, FM ??

It should be FM, and you must pick up the signal from before the audio
filter.  You're looking for "flat unsquelched" in Motorola parlance ;-)

9600bps FSK is generated by modulating the carrier frequency with the
digital bitstream directly, after passing it through a filter to round the
corners off so it doesn't splatter.  As such, the frequency response needs
to be flat from DC to whatever the passband of the IF filter is.

Gordonjcp MM0YEQ

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