Re: [Discuss-gnuradio] UHD USRP sink does not react to gain changes (gr-ieee802-11: between two usrp devices)

[Nasi]

> Meanwhile I use the second laptop and USRP N200 device as the receiver by running the ./ofdm_rx.py. The error rate is very high.

>

So you receive some packets or none?

Yes, I receive hopefully. But the packer error rate is too high. I went through different configurations and gains. And finally I see that the problem is the transmission side. The gain does not have any influence on the error rate.

> The problem is that when I change gain in the USRP sink nothing changes (i tested it using 'wxgui_fftsink').
> (I think it is a software problem since I tested it with another project. There it changes when I change gain.)

Can you please be a litte bit more verbose? Where do you plug in the FFT sink? What do you see? What did you expect to see.

Yes, sure. So I attach FFT sink to the USRP source in the ofdm_rx.grc. You should see an FFT plot like a normal FFT block. I set FFT size to 64 and frequency to the frequency which I transmit or receive. Ok. lets say we do not care what we see, but when I change the gain in the transmitter nothing changes in the plot. You know that the curve dB should go higher, isn't it? However in this case the receiver signal dB is below -80 dB which showa that there is very low signal.
Even I detach the antenna it works, funnily. I testet this with benchmarks to see if it is a hardware problem or not. It seems like smt. is wrong in the transmission side.  Do you have any idea what can cause it?

If you plug it in after the USRP block it is not a problem of the receiver, but here the actual signal might be hard to spot. In that case I would try gr-fosphor. If it is after the signal has been normalised it is obviously independent from the gain setting. I started a readme file with some tips (see github) maybe you find something interesting in there.

Bastian

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NE