Re: 回复： 回复： Problems implementing USRP b210 dual channel transceiver

[Marcus D. Leech]

On 07/12/2022 07:49, 能书能言 wrote:
>     The number of data packets in ① is not correct, but the number of 
> data packets in ② is correct. Therefore, to avoid more problems, I 
> choose ②.
>     By viewing the pictures in the attachment and your explanation, f_ 
> RF is LO frequency? Then the two channels share one LO, so setting f_ 
> Offset adjusts the frequency to f_ target?
>      I tried the following:
>         freq1=   2.4G
>         freq2=   2.39G
>         lo_off1=   5M
>         lo_off2=  -5M
>         samp_rate=300K
>     But the problem still exists, and the bit error rate is very high : (
> Another thing I forgot to say is that I did a dual channel 
> transmission experiment before (I call it experiment A. ), and the 
> parameter settings are the same as when I first set them（freq1 = 2.4G, 
> freq2=2.39G, lo_off1=2M, lo_off2=-2M,samp_rate=300k）,which performs 
> very well. The only difference between experiment A and this 
> experiment now is that the modulation of the signals on the RFA and 
> RFB of experiment A are different. I copied the USRP sink and USRP 
> source components directly from the GRC of experiment A, and the 
> parameter settings are the same, experiment A performed very well, but 
> in this experiment a high BER occurred, so now I am confused where the 
> problem lies
> Best regards！
You need to look *in detail* about how tune_request works.

In particular, the default policy for both the rf_freq and the dsp_freq 
is *AUTO*, which is not what you want in this case:

https://files.ettus.com/manual/structuhd_1_1tune__request__t.html

You likely want to tune the LO to half-way between your two desired 
frequencies, and then use DSP offsets from that.

With a policy of "auto", it will try to tune the chip so that the 
specified frequency appears in the baseband, but using
  an offset tuning--that's not *quite* what you want.

You need to specify the same (in-the-middle) rf_freq for both channels, 
with MANUAL policy, and set the DSP offset
  appropriately, again with MANUAL policy.