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[Discuss-gnuradio] Automatic Fine Tuning for FM demod

From: Marcus D. Leech
Subject: [Discuss-gnuradio] Automatic Fine Tuning for FM demod
Date: Wed, 09 May 2012 21:08:14 -0400
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20111108 Fedora/3.1.16-1.fc14 Thunderbird/3.1.16

I've just updated simple_fm_rcv to implement a simple Automatic Fine Tuning function.

This function measures DC offset on the output of the demodulator block, and uses that to drive a parameter of the freq-xlating filter block that's on the input. It seems to work OK in my simple tests this evening. This is a piece that typically wouldn't be required if using UHD hardware, but the RTL-SDR radios have, ahem, less-than-ideal master oscillators, so I wanted to see if AFT would be

So, in effect, I've implemented a feedback loop within the flow-graph. But it's via a polled value, so it doesn't violate the rules.

Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium

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