Flatness of RX signal

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HB9FXX
Posts: 3
Joined: Fri Jun 18, 2021 4:17 am

Flatness of RX signal

Post by HB9FXX »

Hello all,

after some time trying to properly configure my new BladeRF 2.0 xA4 for reception i come here for some support for my multiple issues.

First of all when trying RX with no antenna attached, but only a 50Ω dummy load on the input connector, the received signal is not flat but rises the more it goes away from the center frequency. The same behavior is also present with a real antenna.

2 screenshots, one with signal acquired with bladeRF-cli and the other with CubicSDR (using SoapySDR behind):
https://ibb.co/23r4RPq
https://ibb.co/HpjFFJD

For the first screenshot the command used was:

Code: Select all

/usr/bin/bladeRF-cli -e "set samplerate rx1 4000000" -e "set bandwidth rx1 3000000" -e "set frequency rx1 2245000000" -e "set agc rx1 off" -e "set gain rx1 40" -e "rx config channel=1 format=bin file=fifo n=0" -e "rx start" -e "rx wait"
With higher gain it seems to get a little flatter, with lower gain even less flat.

Is this expected behavior or am i doing something wrong ?

Many thanks
robert.ghilduta
Posts: 156
Joined: Thu Feb 28, 2013 11:14 pm

Re: Flatness of RX signal

Post by robert.ghilduta »

The side lobes occur at low gains in the AD936x, please see https://ez.analog.com/wide-band-rf-tran ... isn-t-flat and https://ez.analog.com/wide-band-rf-tran ... hape-issue . Increasing gain should flatten the pass band, and by the highest gain, which is what the noise shaping filter is optimized for, it should be almost completely flat.
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