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Re: [Discuss-gnuradio] Trouble understanding multiple independent signal

From: Eric Blossom
Subject: Re: [Discuss-gnuradio] Trouble understanding multiple independent signals
Date: Thu, 20 Oct 2005 12:01:32 -0700
User-agent: Mutt/1.5.6i

On Thu, Oct 20, 2005 at 12:03:31PM -0600, David R. Palchak wrote:
> I'm having trouble understanding exactly how to go about
> sending two independent, real-valued signals to different
> SMA connectors on the same transmit daughtercard.  The
> signals I want to transmit are streams of type short.  Do I
> need to convert these to one stream of complex type and use
> a usrp.sink_c(), or can I interleave them and send them to
> a usrp.sink_s()? 
> Thanks,
> David Palchak

Hi David,

As the software is currently built, you cannot send two independent,
real-valued signals to different connectors on the same transmit
daughterboard.  The reason is that we are using the digital
up-converters in the AD9862, and have the AD9862's configured in
"Dual Channel Complex DAC Data" mode.  See pages 20-21 of the AD9862

Here's a more detailed explanation:

It is possible in hardware to use the two channels on a tx
daughterboard independently, but that would require several changes to
the usrp host library and FPGA code.  For starters, if you need digital
upconversion, you'd need to perform it in the FPGA, not the AD9862.
[We had this working at some point in the distant past, but removed it
since using the AD9862 DUC's saved us a ton of FPGA resources.]

If you only need two independent Tx channels, the quick fix is to use
two Basic Tx daugherboards.  This is supported.  Just tell the USRP
that you're using two channels of data, then provide a stream with two
interleaved channels of I & Q data.  If you like, I can whip up an
example.  Let me know.


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