Possible residual carrier not reported correctly

Hi,
I am using the Basic RX/TX at 24Mhz. Both the tx and rx tell me that
there is no residual carrier. yet, the waveform I send seems to keep
flipping from positive to negative polarity. Is it possible that there
is
residual carrier that is not being reported correctly?

Thanks in advance.
Isaac

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On Fri, Jul 25, 2008 at 02:12:38PM -0700, isaacgerg wrote:

Hi,
I am using the Basic RX/TX at 24Mhz. Both the tx and rx tell me that
there is no residual carrier. yet, the waveform I send seems to keep
flipping from positive to negative polarity. Is it possible that there is
residual carrier that is not being reported correctly?

No, there’s no residual frequency offset.

Are you seeing any over or underruns (“uOuO” or “uUuU”) on the console?
How wide is the signal you’re trying to send?
What interpolation and decimation values are you using?

Try sending it at 10MHz.

What version of GNU Radio are you using?

Have you isolated the problem to the Tx or Rx path?

Eric

Eric,
I have answered you questions inline:

Are you seeing any over or underruns (“uOuO” or “uUuU”) on the console?
Occasionally, I see “u0” on the rx. But, even if i post process data
offline, i still get the “flip”

How wide is the signal you’re trying to send?
The rx interp is 256 and the tx interp is 512 giving a BW=250Khz.
Since I
am just sending random samples, I am using the whole band.

What interpolation and decimation values are you using?
See above.

Try sending it at 10MHz.
I did. The Rx cannot see my signal anymore; a PSD confirms this. Not
sure why… maybe an antenna issue.

What version of GNU Radio are you using?
I do not know what version the radios are. How do i find this out? The
serial numbers are 1460 and 1461 and there is a date on the sticker that
says 4/16/07.

Have you isolated the problem to the Tx or Rx path?
I believe it is in the Rx path. The TX path simply reads up a data
file
of samples and sends them to the USRP… very simple. The RX path
receives
the data and attempts to correlate on the samples I sent. However, I am
noticing that the correlation is postive, then negative, and continues
this
way alternating about every 1000 samples or so.

Isaac


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Eric,
I pulled GNU Radio from the SVN repository no more than 3 months ago.
What do you mean the FPGA had a flipping problem? Wouldnt this affect my
USRP hardware or does the GNU Radio code correct for it?

Isaac

Eric B. wrote:

How wide is the signal you’re trying to send?


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On Mon, Jul 28, 2008 at 12:27:22PM -0700, isaacgerg wrote:

Eric,
I pulled GNU Radio from the SVN repository no more than 3 months ago.
What do you mean the FPGA had a flipping problem? Wouldnt this affect my
USRP hardware or does the GNU Radio code correct for it?

Isaac

I was thinking of ticket:179
http://gnuradio.org/trac/ticket/179
It was fixed in r6764 on the trunk on 10/31/2007.

Eric B. wrote:

On Mon, Jul 28, 2008 at 11:34:01AM -0700, isaacgerg wrote:

Eric,
I have answered you questions inline:

Are you seeing any over or underruns (“uOuO” or “uUuU”) on the console?
Occasionally, I see “u0” on the rx. But, even if i post process data
offline, i still get the “flip”

If you’re getting “uO” your machine is not keeping up. This would
cause a discontinuity in the received data, post-processed or not.

Eric

On Mon, Jul 28, 2008 at 11:34:01AM -0700, isaacgerg wrote:

am just sending random samples, I am using the whole band.
serial numbers are 1460 and 1461 and there is a date on the sticker that
says 4/16/07.

Sorry, not the board, the GNU Radio software you’re running on the host.

There was a problem in the FPGA code that was fixed quite a while
ago (6 or 9 months) where there was some kind of flipping.

Have you isolated the problem to the Tx or Rx path?
I believe it is in the Rx path. The TX path simply reads up a data file
of samples and sends them to the USRP… very simple. The RX path receives
the data and attempts to correlate on the samples I sent. However, I am
noticing that the correlation is postive, then negative, and continues this
way alternating about every 1000 samples or so.

Isaac

Eric

Eric,
When you talk about the FPGA, do you mean that I can repull and
reinstall
the FPGA code for the USRP? This I have never done since the radio has
been
purchased 2 years ago.

Isaac

Eric B. wrote:

I was thinking of ticket:179

Are you seeing any over or underruns (“uOuO” or “uUuU”) on the


Discuss-gnuradio mailing list
[email protected]
http://lists.gnu.org/mailman/listinfo/discuss-gnuradio


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Eric,
I read the ticket. We are just sending float data and it doesnt
appear
that the arms are getting flipped, but that over time, their phase is
changing. Our correlation peaks go from being very positive to being
very
negative over a gradient.

Any ideas?

Isaac

Eric B. wrote:

I was thinking of ticket:179

Are you seeing any over or underruns (“uOuO” or “uUuU”) on the


Discuss-gnuradio mailing list
[email protected]
http://lists.gnu.org/mailman/listinfo/discuss-gnuradio


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On Jul 28, 2008, at 2:09 PM, isaacgerg wrote:

Eric,
When you talk about the FPGA, do you mean that I can repull and
reinstall
the FPGA code for the USRP? This I have never done since the radio
has been
purchased 2 years ago.

Isaac

The FPGA code is dynamically loaded when the USRP is initialized. As
long as you have an installed copy of GNU radio newer than 10/2007 you
should already be using the updated RBF file which is the FPGA code
image.

  • -Dan
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