Re: [Discuss-gnuradio] Can I do this?

[mgray]

Another trick to get higher frequencies is to use an image that is 
produced the DAC.  If you program the DAC to 29.3 MHz, you'll also get RF 
at the SampleRate +/- DAC Freq.  So you'll get a signal at 128 - 29.3 and 
128 + 29.3.  So in this case 98.7 and 157.3. The signal levels will be 
lower, but with the proper bandpass filter and amplifier chain, you can 
generate a complete signal.  

I don't recall if there is a low pass filter on the DAC channel.  If there 
is, you'll need to remove the filter to get the images.  With a short 
piece of wire stuffed in the SMA connector, you could broadcast across the 
room to an FM receiver.


For an example of the band pass filters/RF chain, view:

http://www.kd7lmo.net/picobeacon_hardware.html

This is setup for operation in the UHF band at 445 MHz.


On Tue, 27 Sep 2005, Ilia Mirkin wrote:

> You simply can't do that. The hardware on the USRP has a DAC capable of
> 128MS/s (iirc), which means that AT MOST you could get it to put out a
> 64 MHz signal. If you shift over by 98.7MHz, then that'll be past the
> DAC's ability to reproduce an accurate signal (it will in fact fold over
> to like 98.7 - 64 MHz, I think). Coincidentally, the -c option usually
> takes Hz, not MHz, so you're shifting it over by 98.7Hz. (Didn't look at
> the actual code, so I could be wrong on that.)
> 
> If you want to transmit in the FM band, you will need an upconverter
> that will take the baseband signal out of the USRP and move it over to a
> higher frequency.
> 
> Good luck.
> 
> On Tue, 2005-09-27 at 19:19 -0500, Jorge Chávez wrote:
> > Hi gnuradio's
> > 
> > I'm trying to FM TX, can I do this with the fm_tx4.py:
> > 
> > address@hidden:/home/gr-build/gnuradio-examples/python/usrp # ./fm_tx4.py
> > -c 98.7
> >  
> > When I run it I get this:
> > 
> > address@hidden:/home/gr-build/gnuradio-examples/python/usrp # ./fm_tx4.py
> > -c 98.7 ddc_freq = 98.7
> > len(interp_taps) = 356
> > >>> gr_fir_fff: using SSE
> > len(interp_taps) = 356
> > len(interp_taps) = 356
> > len(interp_taps) = 356
> > TX d'board A: Basic Tx
> > TX d'board B: <none>
> > 
> > But I can't hear in a Radio (98.7MHz) what I record in audio-0(-4).dat
> > 
> > What am I doing wrong?
> > what is missing?
> > I'm thinking that it yust work for 29.326MHz, but my convencional
> > radio system is not alowed to do this frecuency.
> > 
> > Thanks for your answers, and sorry for my english..
> > 
> > Jorge Chávez
> > _______________________________________________
> > Discuss-gnuradio mailing list
> > address@hidden
> > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
> 
> 
> 
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