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 for! I based my program in the example max_power.py. What can I do to generate a signal, on which I can control perfectly the frequency, through the USRP? The tx parameters are: ####SIGNAL##### waveform = sin freq = 1MHz sample_rate = 128e6/16 amplitude = 16e3 ####USRP###### set_tx_freq = 1 MHz set_mux = 0x98 nchannel = 1 set_interp_rate = 16 Any idea, constructive comment, example is welcome ! Thank you all!
on 2008-12-09 12:08
on 2008-12-09 13:58
Hi, 1) USRP1 minimum interpolation rate is 16. You cannot go lower. 2) If you want to transmit signals, use usrp_siggen.py or modify it to do what you require. Regards, Firas