Hello Javier, the "slantedness" of the constant frequency tone (the fact that it's not a perfect circle) looks like quite a bit of IQ imbalance to me – how many samples are those? What frequency did you work with?
The other two graphs, based on the const freq graph, look familiar – one "swing" has about the shape of the const freq loop, and it slowly rotates – the effect of the frequency difference between transmitter and receiver. So, what worries me is the fact that your constant frequency plot doesn't have the same dimension in I and Q! Best regards, Marcus On 08.11.2017 12:48, Javier Coronel (Expo Impex, S.L.) via USRP-users wrote: > 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! > > > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
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