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Re: [Discuss-gnuradio] EDACS Control Channel

From: Rick Parrish
Subject: Re: [Discuss-gnuradio] EDACS Control Channel
Date: Sat, 15 Apr 2006 22:43:40 -0500
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Ryan Pape wrote:

Given my rudimentary knowledge on the topic (and gnuradio in general)
which (if any) of the examples present would be my best starting point
given that I'm hoping to do this, even initially, right off the air
with the TV RX?
To follow-up on Ryan's original question ... I've looked at the examples and documentation. A few grumbles ...

1. I can't find straightforward examples.
2. there are no comments (no, the GPL preamble doesn't count)

Part of the problem (for me at least) is that I don't write Python. It's just not my choice for scripting.

Let me see if I can translate what Ryan wants into the types of building blocks found in GNU radio.

1. something to convert the USRP into a NBFM receiver. I've seen an NBFM example but again, it's all python so I can't tell where to modify it for this application. I'd like to break this out into two peices. 1a. "how-to" example that downconverts an RF signal into an IF or baseband signal 1b. "how-to" example that builds on the above to produce AM, FM, or NBFM audio from the baseband or IF samples; this includes various bandwidths ie. 100 khz, 30khz, 15khz and 8 khz. 2. in the above NBFM block-chain there needs to be a source that produces demodulated audio samples at a decent "hi fi" sample rate; there should be no de-emphasis or low/high pass filtering of this audio (functionally equivalent to unfiltered FM discriminator audio).

If we can get audio samples at something like 44100, 48000 or even 96000 samples per second ... we're almost home. It doesn't take much more work to handle clock recovery and crunch the audio samples into a 9600 baud bitstream.

Some other nice-to-have how-tos are:

1. read data from an audio file (with the audio chunks delivered in "real" time) and/or record to an audio file. 2. a sample processing block that adds some sort of audio effect along with example plumbing that uses the audio.in and audio.out (PC microphone and speakers).

Someone like Ryan could use #1 or #2 as a way to test his code without an actual USRP.


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