Out of band rejection becomes worse when the AGC is used

Projects LimeSDR
1

Hello all,
When I debugged the LimeSDR USB board, firstly, I used signal generator to generate the unmodulated carrier fc with frequency offset 1MHz, then sent it to the board with suitable interface. through GUI, I set the VCO frequency to fc, and debugged the board with good suppression for Unwanted SSB。 pls refer to the following screemshot

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When I chose the AGC under the RXTSP tab and enable AGC under the TRX Gain tab, pls refer to the following screemshot respectively.

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found the suppression for Unwanted SSB became worse,pls check the following screemshot… Could you pls help me the reason?
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Meanwhile, I could not find the process how was the LNA, TIA and PGA gain controlled by the AGC, could you pls help me to explain the controlling flow of AGC, especially in the analog end.

Zack

martywittrock

Zydrunas Tamosevicius

Thanks a lot!

2

MCU AGC algorithm for controlling LNA and PGA : https://github.com/myriadrf/LimeSuite/blob/master/mcu_program/common_src/lms7002m_agc.c#L162

3

Thanks Ricardas for your quick response. Are these any documents to stress the process of AGC working flow?