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EDIT: I have succeeded in getting the AM receiver to work, by replacing the AM Demod block with a Complex To Mag, and a Band Pass filter (this is noted as an alternative in the AM Demod docs).

Consequently, while I've proved that most of what I did was valid, I'm still interested to know what I did wrong in the use of AM Demod below, if anyone can spot my error.


I'm completely new to SDR, and I fear I'm making very basic mistakes. I want to receive AM transmissions in the air band, but so far my only success has been with FM public broadcast.

Here's the gnuradio companion flowgraph that is the best I've been able to come up with so far.

enter image description here

This is based on the example of the AM Demod block, described here: enter link description here

This, runs and outputs static in a moderately convincing way, but no meaningful audio. I live 1 mile away from my local airport, and their ATIS signal is on 126.1, yet, when I select that frequency, I simply get the same static.

I have also assembled a trivial waterfall diagram flowgraph which shows a trace at 126.1 too, which seems to suggest the signal is strong enough for this receiver, even with it's feeble 1-foot-long whip antenna.

I do get a warning message when the graph runs:

Using device #0 Realtek RTL2838UHIDIR SN: 00000001
Found Rafael Micro R820T tuner
[R82XX] PLL not locked!

However, I'm inclined to think this is not significant, since I get the same message when I run the FM receiver that works quite well.

Can anyone tell me if there's something wrong with the flowgraph, or the values therein? Or perhaps offer any other suggestions?

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    $\begingroup$ Hello Toby, and welcome to ham.stackexchange.com! $\endgroup$
    – rclocher3
    Oct 11 at 23:42

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