Dbsrx agc?

GNU Radio
1

Hi,

I am running an experiment where I would like to monitor the magnitudes
of a
bursty, constant-envelope signal using the USRP and a DBSRX receiver. I
am
seeing some quasi-periodic amplitude transitions and wanted to know if
this
could be related to an AGC. Why I believe it is AGC-related is because
the
amplitude transitions occur ONLY on leading-edge boundaries (and never
intra-burst). What I see magnitude-wise in Matlab based on data from
usrp_rx_cfile.py is something like:

———|||||||||||||||———||||||||||||——|||||||||_—
… (magnitude vs. time — please excuse my ascii art:)

where there are really only two magnitude levels ( ||| and — , and
interburst ‘silence’ is denoted as _ ). Furthermore, I ran another
experiment using the same bursty, constant envelope signal using 2 DBSRX
receivers in a single USRP (with the proper mux of 0x3210). Both
receivers
experienced the same phenomenon, however there was some more
‘interesting’
behavior. When the DBSRX on side A transitioned from high to low, the
DBSRX
on side B transitioned from low to high. This was the case for multiple
runs, and again the transitions only occured at leading edge times. In
summary my questions are as follows:

  1. Is there an AGC in the DBSRX?
  2. If yes, can I turn it off?

Thanks in advance for any ideas, recommendations, or comments!
Rob

–
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2

Robert M. wrote:

Hi,

  1. Is there an AGC in the DBSRX?
  2. If yes, can I turn it off?

The only gain control on the DBS_RX is entirely under software control.
If the software doesn’t control it, it stays the
same. I’m not sure why you’re seeing magnitudes “inverted” between
DBS_RX.

Could you perhaps share the code?

I have an application that uses two DBS_RX, looking at two different
polarizations. They don’t see this
phenomenon at all.

–
Marcus L.
Principal Investigator, Shirleys Bay Radio Astronomy Consortium

3

Hi Marcus,
Thanks for the quick response. Attached is my code for piping data from
2
DBSRXs to separate files. I simply made a few modifications to the
multi_file.py script in ~/gnuradio-examples/python/multi-antenna/.
After
seeing the phenomenon over multiple runs I then switched to using a
single
DBSRX and the standard usrp_rx_cfile.py script. Using both DBSRXs I
witnessed the same magnitude oscillations, with them only occuring at
leading edge transitions.
Thanks!
Rob

Marcus D. Leech wrote:

If the software doesn’t control it, it stays the

http://www.nabble.com/file/p24046153/MyMultiFile2.py MyMultiFile2.py

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