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

[Bastian Bloessl]

On 12 Dec 2013, at 15:26, Nasi <address@hidden> wrote:

> 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.

Just to be sure: do you have the current version? (some weeks ago I normalized 
the signal power to 1 without pushing updates of the flow graphs. That lead to 
distorted signals. In that case, changing the gain does not help.)

> 
> 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?

Thanks, I guess the problem is that just very few samples of your incoming 
stream belong to WiFi frames. So chances are that the frame is not visualised 
at all (I think that the FTT sink uses a subset of the samples based on the 
sample rate and the update rate of the GUI). If you really want to stick to 
this approach I would recommend to  checkout gr-fosphor. I found it really 
helpful.

https://www.youtube.com/watch?v=mjD-l3GAghU

Best,
Bastian