[USRP-users] Amplitude oscillation on B210

Javier Coronel (Expo Impex, S.L.) jcoronel at expoimpex.com
Wed Nov 8 06:48:43 EST 2017


Hi all!,

I am using a setup where Tx antenna is in front of Rx antenna, this way I
can measure all the signal path and environment interferences of the
transmission.

When I send an AM signal at a constant frequency, everything is right, I
receive the same signal (the amplitude depends on many factors, but it is
almost constant).

But if I send a FM signal starting at some frequency and gradually increase
that freq. in some amount, I get amplitude variations of the received
signal. This is consistent using a direct cable connection. Also I dumped
the wave I send into a file to check if everything is OK, and it is so.

Attached you can see polar representations of the I vs Q signals received
for the cases of constant frequency, 10 Hz variation and 50Hz variation.

I saw the schematics and the only reason I can figure is due to the switch
(SKY13335−381LF) or some kind of AGC digital filtering on the path. I set
the gain manually, but I am not sure if this is also affected by any other
configuration.

Should I call any function to get the same amplifier response as in the
case of constant frequency? Thank you in advance!.

Have a nice day!
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