VGA gain is limited to 30 dB, but MAX2830 allows for 62 dB.

rigexpert / gr-rigexpert

Fobos SDR receiver Complex IQ signal source block for GnuRadio. Full sourse code.

GNU Lesser General Public License v2.1

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VGA gain is limited to 30 dB, but MAX2830 allows for 62 dB. #2

Closed godsic closed 3 months ago

godsic commented 3 months ago

According to p. 21 of MAX2830 datasheet it allows for up to 62 dB of VGA gain (5 bits in Reg. 11). However in https://github.com/rigexpert/gr-rigexpert/blob/a52589b56945ab7865d48dc87d89e9addf354dc0/fobos/fobos.c#L1222 its value is limited to 30 dB (maximum allowed value in the register is 15 instead of 31). Is it typo or done intentionally?

rigexpert commented 3 months ago

Maximum VGA gain is deliberately limited to idx=15, because our MAX2830 has inexplicable behavior on higher gain index. I and Q channels gains are significantly different causing huge IQ imbalance. Datasheets not always provide completely correct information.

godsic commented 3 months ago

@rigexpert Fair enough, thanks for the explanation.

waterwin commented 2 months ago

The VGA Drop Down list is showing dB values from 0dB to 30 dB in steps of 2 dB, when choosing 30 dB the GNU Source block is showing 15. That is confusing.