Re: [Discuss-gnuradio] How to configure SBX with two channels, one for communications, one for sensing?

[Alex Zhang]

Thanks!

I am trying to set up two channels on RX2 as Nick said. And the subdev is set as "A:0 A:0". Please see the attachement for the GRC flow graph.

But my problem is that it seems that both the channels can not receive the expected signal(I am using an OFDM transmitter for test).
The single channel with frequency of 908M or 928M works well as I can see the OFDM spectrum from the observing FFT plot window.

On Mon, May 21, 2012 at 5:37 PM, Josh Blum <address@hidden> wrote:

On 05/21/2012 03:09 PM, Alex Zhang wrote:
> Hi,
>
> What I want to do is try to use the two antennas of SBX simultaneously.
>
> The TX/RX is used for duplex communications and the RX2 is for sensing. The
> two antennas are working different frequencies.
> But this solution seems to be unfeasible, as someone said the receiver
> chain of SBX is the same. The TX/RX and RX2 can not work simultaneously.
> As suggested in the community, I am trying to using 3 frequecies on one
> antenna (TX/RX): f1, f2, f3.
>
> f1(tx) and f2(rx) are used for FDD duplex communications,and f3 is for
> sensing path. And f2 and f3 are within the 40MHz difference.
>
> My problem is how to set it in USRP source block for this kind of
> configuration? Does anybody has such example? And I met the error like
> below:
>
> Runtime error:vector::_M_range_check
>
> which seems to be caused by incorrect setting of subdev. However, I don't
> know what the valid value fo subdev in such kind configuration.
>
>

Correct, you can only receive from one antenna at a time. If your RX
frequencies of interest are reasonably near in frequency, lets say 40
MHz, you can use multiple DSPs in the FPGA as a kind of 2 channel
filterbank.

You can set the subdev/frontend spec to "A:0 A:0", this will map the
frontend A:0 to both DSP0 and DSP1. If you setup the USRP source for 2
channels, DSP0 will be output 0 and DSP1 will be output 1.

Be careful with the tune_request so that you are setting the rf
frequency to the same setting, but with different target frequencies to
get the DSPs to shift appropriately. There should be some mention of
tune request in the docs inside the USRP source block properties dialog
in GRC.

-josh

>
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-- 

Alex,

Dreams can come true – just believe.

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