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Gain range - again!

Posted: Wed Oct 11, 2017 8:22 am
by mike_haben
OK, a variant on my previous question:

Why does mir_sdr_RSP_SetGr() error out on values of gain-reduction parameter gRdB above 59?

The "Default Gain Tables" document lists internal settings of baseband gain-reduction, mixer GR and LNA GR for gRdB up to 102, 85 or 83 depending on the frequency-band. So how do I get access to these higher levels of gain-reduction?

Thanks, Mike H.

Re: Gain range - again!

Posted: Thu Oct 12, 2017 9:56 am
by mike_haben
Finally worked it out - I need to use the LNAstate parameter of mir_sdr_RSP_SetGr() to switch the LNA and mixer gains. The API Specification document would be less confusing if the Gain Reduction Tables were not in a completely separate section (or even document!) from the functions they relate to, and if the terms "RSPI" and "RSPII" were replaced with "RSP1" and "RSP2"! (Doesn't help that I'm driving the RSP2 from a Python script, via the SoapySDRPlay layer).

Also the values in the gain-reduction table are not accurate across all frequencies. For the RSP2 in "Band 4/5" it states (2nd table in section 5.3):

Code: Select all

LNAstate:    0   1   2   3   4   5
LNA GR (dB): 0   7   10  17  22  41

At 870MHz, I measure 0, 7, 13, 20, 20 and 39dB.

Hope this helps somebody...