Sine output between packets

It seems my old patch that zeroed out the output of the USRP didn’t make
it into UHD- we’re seeing a constant sine output between packets- and in
our case this messes with the receiver unless we use some custom TX
cards that have an amp we can shut down with ATR.

Is there any way to fix this?

On 09/26/2011 05:36 AM, Tom R. wrote:

I’ve never noticed this with my work with the UHD. There are various
commands issued to the USRPs to turn it on and shut it off between bursts.
Maybe there’s something missing in the gr-uhd.

On the other hand, Josh and Nick have been working on using tags with gr-uhd
on the transmit side, which should fix your problem.

Any comments from the UHD folks?

The usrp1 shutdown mechanism in UHD is a little soft (because there is
no inline metadata with the samples). However, if you mark end of burst,
then the transmitter should get disabled.

You can do this w/ tags using this branch:
http://gnuradio.org/cgit/jblum.git/log/?h=mergme/uhd_tags_impl_on_master

I would verify that the behavior w/ eob is OK for you on usrp1 by
modifying some uhd (non gnuradio) examples before getting into tags.

And BTW, I didnt know about this patch. The UHD usrp1 images match the
gnuradio ones, so its definitely not in there:
http://gnuradio.org/redmine/projects/gnuradio/repository/revisions/4b5e1238492fe40727d19abefe22ae448c720419

It looks like the patch involves verilog changes. Is this an image that
you can just build and drop in place of the existing one or does it need
host code support? Have you tried it?

-Josh

On Mon, Sep 26, 2011 at 05:36, Tom R. [email protected]
wrote:

I’ve never noticed this with my work with the UHD. There are various
commands issued to the USRPs to turn it on and shut it off between bursts.
Maybe there’s something missing in the gr-uhd.
On the other hand, Josh and Nick have been working on using tags with gr-uhd
on the transmit side, which should fix your problem.
Any comments from the UHD folks?

Brett, if you are using anything beside the BasicTX or LFTX, then it’s
also possible you are seeing LO feedthrough/DC offset in the transit
mixer, which results in a carrier output between packets.

Johnathan

On Sun, Sep 25, 2011 at 8:07 AM, Brett L. Trotter
[email protected]wrote:

It seems my old patch that zeroed out the output of the USRP didn’t make
it into UHD- we’re seeing a constant sine output between packets- and in
our case this messes with the receiver unless we use some custom TX
cards that have an amp we can shut down with ATR.

Is there any way to fix this?

I’ve never noticed this with my work with the UHD. There are various
commands issued to the USRPs to turn it on and shut it off between
bursts.
Maybe there’s something missing in the gr-uhd.

On the other hand, Josh and Nick have been working on using tags with
gr-uhd
on the transmit side, which should fix your problem.

Any comments from the UHD folks?

Tom

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