On Fri, Sep 30, 2005 at 10:47:47AM -0500, Jorge Chávez wrote: > I'm trying to FM TX with the fm_tx4.py but it doesn work for comercial FM > Band (88 to 108MHz) but I need to TX in this frecuencys. > Whe I submit my needs in the gnuradio discuss I get the next tip: > > 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.
> Does it realy works? How and where can I change the sample-rate to make > this image? Yes. It really works. No sample rate change required. If you have access to a spectrum analyzer, this is easily verified. Richard Lyons' book "Understanding Digital Signal Processing" has a very clear explanation of the phenomenon. There are images produced each 64 MHz (sampling rate / 2). Every other one of them has the spectrum inverted, but that won't matter for FM. You might try googling for "Nyquist zone" or "bandpass sampling" http://www.national.com/appinfo/adc/files/Undersampling.pdf Note that broadcast FM is much wider-band than narrow-band FM. Very similar, but putting together a wfm tx block would make sense. If you just connect a wire to the SMA connector and the FM receiver is close by you can probably hear it. For a real solution, you'll want a bandpass filter and amp as described above. > Sorry for not submit this to the Discuss. > and sorry for my english No problem with your English. It's completely understandable. But please post questions to the list. > I hope your answer, and your advise. > Thanks > > Jorge Chavez Eric _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
