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Re: [Discuss-gnuradio] Can another DUC chain be added to USRP N210?

From: Anisha Gorur
Subject: Re: [Discuss-gnuradio] Can another DUC chain be added to USRP N210?
Date: Sat, 29 Sep 2012 12:45:37 -0400

Thanks Josh, 
What I am looking for on the TX side of things is basically the same thing I have on the RX side. If I set the subdev spec on the basic RX to "A:A A:B" and then use usrp->set_rx_freq(uhd::tune_request_t(freq)) for each channel, I get two separate rx channels, both with their own IQ pairs. On the TX side I only manage to have one IQ pair, as in I through TX_A and Q through TX_B. We were trying for a 4 channel transmit on 2 USRPs, so that they could all be connected by s MIMO cable. One more question, when you say "too complicated to be worth it", generally, what kind of modification would be necessary?
Thanks for your time!

On Fri, Sep 28, 2012 at 6:36 PM, Josh Blum <address@hidden> wrote:

On 09/28/2012 08:49 AM, Anisha Gorur wrote:
> Hello All,
> I am using a USRP N210. When i set the subdev spec for my basic RX
> daughterboard as "A:A A:B" I can receive two channels. However, if I try to
> do something similar for the basic TX I get an error like "The user
> specified 2 channels, but there are only 1 tx dsps on mboard 0." I assume
> this is because there is only one DUC chain in the N210. Is there a way to
> modify this so that I can have two DUC chains in the same way that I have
> two DDC chains?
> Thanks,
> Anisha

I think adding two complete DUC chains into N210 would be too
complicated to be worth it.

Is there something specific that you cant do with the single DUC chain?
As long as the cordic is set to zero, I and Q will remain completely
separate from host samples, all the way to the SMA connectors A and B.

Otherwise, perhaps you need a different rotation for I vs Q? I think
that would be better accomplished by two different cordics. Then perhaps
a custom DSP in the FPGA is for you:

I hope that helps.


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Anisha Gorur
Class of 2012
Electrical Engineering

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