Forum: GNU Radio Help with USRP

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Ronaldo N. (Guest)
on 2008-12-09 13:08
(Received via mailing list)
Hello everybody!

I have series of questions dealing with GNU Radio / USRP.
I am trying to tx a controlled simple sine signal using a USRP v1. The
specs I am using are:

* SIN Frequency: 1 MHz
* SIN Amplitude: 16k (not relevant in my case for now)
* SIN Sample Frequency = dac_rate/interpolation_rate
* dac_rate = 128 MS/s
* interpolation_rate = 36
* set_tx_freq = 1 MHz

This produces two tones : the first one at 1.5 MHz and the second one at
2 MHz that I cannot explain !

I tried to change the interpolation rate to 4, 8, 16... but for values
less than 36, I see a "UuUuUu..." sequence appearing on the screen. This
means that my computer is not providing the samples fast enough. My
hardware at this moment is a Celeron@1.5GHz, 1Gb of RAM.

To overcome this, I put my HD in a Quad-Core, 8 Gb of RAM, and tried
again. This produces the same results, but I was able to reduce the
interpolation rate down to 16. Less than this rate makes the "UuUu..."
appear again. So, with interpolation_rate = 16 the tones seen on the
spectrum analyzer screen went down from 1.5 MHz to ~1.3 MHZ and from 2
MHz to ~1.7 MHz.
I've been trying to change all available parameters (the interpolation,
frequency, amplitude, etc) but the result is never what I am looking

I based my program in the example

What can I do to generate a signal, on which I can control perfectly the
frequency, through the USRP?

The tx parameters are:

waveform = sin
freq = 1MHz
sample_rate = 128e6/16
amplitude = 16e3

set_tx_freq = 1 MHz
set_mux = 0x98
nchannel = 1
set_interp_rate = 16

Any idea, constructive comment, example is welcome !

Thank you all!
Firas A. (Guest)
on 2008-12-09 14:58
(Received via mailing list)

1) USRP1 minimum interpolation rate is 16. You cannot go lower.

2) If you want to transmit signals, use or modify it to
do what you require.


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