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From: | Chuck Swiger |
Subject: | Re: [Discuss-gnuradio] fm, vector_source |
Date: | Sat, 25 Sep 2004 09:50:59 -0400 |
At 11:20 PM 9/24/2004 -0700, you wrote:
On Fri, Sep 24, 2004 at 05:28:25PM -0400, cswiger wrote: > Hello - > > Q: How is gr.frequency_modulator_fc() used? I see it takes > a 'sensitivity' arg, a float signal in and produces a complex out. > What is being frequency modulated how? > If you look in CVS, gnuradio-examples/python/usrp1/fm_tx4.py implements a four channel FM transmitter. [Each instance of the pipeline ought to have a "pre-emphasis filter", but that's just an IIR. The output is perfectly intelligible without it.] Eric
Ok, I see - the modulator prepares a signal from the audio that is *later* mixed
with your local osc to create the FM signal. I was confused by something called a 'modulator' with only one signal input ;) The examples help a lot.I made a quicky demo here: http://webpages.charter.net/cswiger/fm_modulation.html
which will get a lot more detail such as how to calculate k for deviation etc. This would be a good point to learn how the interperlating filters work too. --Chuck
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