Re: [Discuss-gnuradio] Multiplexing modulators

[John Ackermann N8UR]

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