Re: [Discuss-gnuradio] Issue with basic FM receiver

Hi Ludovico,

On Thu, 2019-09-12 at 12:11 -0700, Ludovico Cavedon wrote:
> Hi Marcus,
>
> Thank you for your reply. The Frequency Xlating FIR filter should be
> already doing the decimation to being samp_rate down to 48k.

Not really – it does a decimation by a factor of 20, whiche means your
1 MS/s becomes 50 kS/s.

> However I found out that formula for the Quadrature Demod gain was
> using samp_rate instead of audio_rate (48k) and the gain was
> excessively high.
> Having fixed that, now it works.
>

Interesting! If you're not experiencing hiccups after some time (when
buffers have run full, because your audio device consumes at 48 kS/s,
while your signal processing chain feeds in 2 kS/s more than that),
either the RTL dongle or the sound card are lying about their actual
rate :)

However, you're right, this should be "close enough" to work for short
terms, albeit audio frequencies should still be a bit off (by 4%).

Best regards,
Marcus

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