Re: [Discuss-gnuradio] [USRP-users] Can use WBX to receive dual channel?

[Josh Blum]

On 01/13/2012 11:59 AM, Scott Johnston wrote:
> Hi Josh,
> 
> I am attempting to do what you described below, but I am seeing two
> problems. First, I see a power difference of about 30 dB going from one
> channel to two. Second, when I tune the second channel 100kHz away from
> the first, the first channel moves 100kHz and the second moves by 200kHz.
> 
> The one_channel picture is from the standard uhd_fft.grc in the examples
> folder. I am generating the signal by using an FRS walky-talky.
> 
> Thanks for any help
> 

So, while you can receive two channels, you still only have one RX
frontend to tune. You need to be careful when you tune. Suppose you want
one channel at f0 and another at f1, and LO to be at the center:

tr = uhd.tune_request(f0, rf_freq=(f0 + f1)/2,
rf_freq_policy=uhd.tune_request.POLICY_MANUAL)
usrp.set_center_freq(tr, 0)

tr = uhd.tune_request(f1, rf_freq=(f0 + f1)/2,
rf_freq_policy=uhd.tune_request.POLICY_MANUAL)
usrp.set_center_freq(tr, 1)

So, there is more than one way to tune everything, but this should give
you a good idea (and you can do uhd.tune_request in grc BTW).

It also dawned on me that it would be a lot less verbose if the whole
POLICY_MANUAL thing was set automatically and not specified by the user
since I'm sure thats what the user wants by specifying the rf_freq
explicitly in the first place. Anyhow...

-Josh