— On Fri, 12/19/08, Dimitris S. [email protected] wrote:
the description should be changed to show that:
- blks2.wfm_tx can receive a maximum audio rate of <=16k
(instead of > the declared >= 16k)
- blks2.nbfm_tx can receive a maximum audio rate of <=
4.5k (instead of >= 16k)
I hope this is clear enough…
I think you have mixed between audio frequency bandwidth and audio
The following example will explain it :
Suppose that you want to transmit nbfm signal for an input audio signal
with maximum bandwidth of 3 KHz. Suppose also that this audio signal is
digitized by (lets say) 32K PCM encoder which results in digitized audio
rate of 32K.
To produce nbfm signal, we do the following:
Ensure that the incoming digitized signal (32K) does not contains any
frequency components above 4.5 KHz (this is done by a digital FIR low
Software interpolate the output of the digital FIR (32 K) to a rate
suitable for transmission (lets say 256K) with interpolation rate of 8.
Do an FM Pre-emphasis to this 256K signal (this is how it was done in
the nbtx.py). The output is also 256K.
Feeding this 256K to a frequency modulator (VCO) which produces
complex output signal.
Stream this output complex signal to the USRP with interpolation rate
of 500 to produce 128M which is fed to its DAC.
I hope this is clear now.