Does that "ghost" signal change offset as you increase and decrease your sample rate?
-Sam On Tue, Oct 22, 2019 at 2:16 AM Skorstad,Jørn via USRP-users < usrp-users@lists.ettus.com> wrote: > Hi list, > > > > I am writing a C++ software which will scan through a given frequency > range and perform an fft. The software seems to do what it should, however > something weird happens when using LO offset tuning. With the following > settings all looks correct: > > > > Sample rate 6.4M – master clock 51.2M – 512 byte num_samples/binsize – > offset 0. However I can clearly see the DC peak for every «jump» in > frequency. > > > > With the same settings as above and a 3.2M offset there is a «ghost» > signal 3.2MHz below the real signal, which mirrors the real signal with > slightly lower amplitude. This happens everywhere in the spectrum where > solid signals (approx 40-50 dBuV) are present. Using the command > tune_request(freq, offset) and usrp->set_rx_freq(tune_request) to set > frequencies. Have also tried with different gain settings from 0-40, no > change. Have also tried with 10 dB attenuator between antenna and the > radio, no change. > > > > The same happens on other sample rates and offsets as well, the ghost > signal is always the same as the offset (+ or -). I am using UHD_3.14.1. > Have also tried changing rx_bandwidth without any change. > > > > Is it possible to use LO offset and eliminate the «ghost» signals, or is > this some radio/DSP limitation? I have pictures showing the problem > clearly, I can send directly by email if necessary. > > > > Thanks, > > Jorn > > > > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >
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