Dear Marcus, > How wide is your signal?
My signal is 25 KHz wide, centered at 25 KHz. (I mix the baseband signal with a sin function at 25 KHz)
Then find the nearest sample rate > your_bandwidth that satisfies the desired outcome that the computed interpolation rate (64.0e6 / desired_rate) is an even number. If the signal has artefacts that "spill" outside the required sample rate, then, yet, filter it first.
While experimenting, I discovered that with 870 KHz sampling rate works, i.e. without the half-band filter problem. However, I get the baseband signal mirrored at 50 KHz lower than the center frequency configured in the USRP. It seems like related to the sampling theorem (I mean aliasing, 2*Fmax=Fs)
I can't figure out how the USRP works internally, and why moves the baseband signal to the transmitting frequency (Yes, I'm not an RF/DSP expert, just intermediate :) Looking on-line,I found out that the function block diagram is something like: CIC (Intepolation) -> half-band filter -> DAC -> TX. Can you confirm it?
I appreciate.
on Aug 01, 2013, *embyte* <emb...@madlab.it> wrote: Hey Marcus, thanks for answering. > (1) 720Khz is not an exact integer fraction of 64MHz (the sampling rate > of the device)--so it rounded > > (2) It's warning you that you'll get a "humped" frequency response with > more rolloff than you'd like, due to the rounded-down sample rate > requiring an interpolation rate that is not divisible by two. If I understood correctly, this it means that the transmitted signal gets filtered more on the edges than expected? Note that by setting a sampling rate of 720KHz, the transmission and receiving work fine. That is, can I fix the sampling rate warning and preserve the transmitted signal by modifying the sampling rate (e.g. to 480KHz) and by adding a band-pass filter before the USRP sink block? Thanks for your insights. I appreciate. _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org <mailto:Discuss-gnuradio@gnu.org> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
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