Friday, June 24, 2011

Re: [Discuss-gnuradio] Multiplexing modulators

Marcus D. Leech said the following on 06/21/2011 07:54 PM:

> I have an example, in GRC, attached.
>
> It uses an audio source, which is common to all three modulators, this
> goes to a fractional interpolator to interpolate up to the basic
> sample rate of 200Ksps, which is an integral divisor of 100Msps.

After a couple of days away, I'm able to get back to this. Thanks very
much, Marcus, for the example. It perfectly shows how to do what I want
-- it's amazing how a block diagram coupled with a very few words can
explain a concept. GRC is a wonderful thing!

The project might be of some interest to the ham radio folks in the
group. I thought it would be a very neat demo of SDR capabilities to
program a multi-channel repeater using USRP. The final version will
have 4 NBFM input channels on the 2m ham band, mapped to 4 NBFM output
channels on the 70cm band (going crossband hugely simplifies the RF
plumbing issues).

I'm not actually putting this on the air, but plan to show it at local
ham radio club meetings as a demo of what you can do with SDR beyond the
paradigm of the traditional HF transceiver using PowerSDR. In a live
demo, it'll be fun to play with the flow graph to show how truly
definable an SDR is. I'll put the .grc and .py files on line once it's
working to my satisfaction.

Next project after this is a linear transponder similar to that used on
the ham satellites, translating all the signals in a chunk of bandwidth
from one frequency range to another.

John

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