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Re: [Discuss-gnuradio] question about mux

From: cswiger
Subject: Re: [Discuss-gnuradio] question about mux
Date: Thu, 25 Aug 2005 16:39:27 -0400 (EDT)

On Thu, 25 Aug 2005, Martin Dvh wrote:

> Hi Chuck,
> >
> > When the other cable between J19 & 48 is removed the scope
> > channels 3 & 4 flatline, just as expected.
> Just checking we understand each other.
> If you remove the cable between J19 & 48 both 1&2 and 3&4 receive channels 
> flatline?
> The purpose of my question is to see if the two channels interact 
> (cross-modulate).
> This is easally seen if you just pas through one of the channels and see if 
> the waveform of the still connected channel changes.
> If it changes, there is some interaction.
> If it doesn't change, there is some other problem.

Just two channels flatline when one cable is disconnected - when J19 is
disconnected channels 1&2 go flat, but 3&4 are still there.  And when J18
is disconnected channels 3&4 go flag, and 1&2 are sill there.

The Rx side makes sense - it's the Tx side I don't understand.
With Tx mux = 0x0008 there's still a signal coming from DAC1, or at
least from J49.

Oh, the docs in usrp1_sink_base.h and usrp1_source_base.h  point
out that in set_tx_freq and set_rx_freq the channel must be 0.
So it looks like all DUC and DDC must be at the same frequency.


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