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Re: [Discuss-gnuradio] XCRV2450 tx gain

From: Nick Foster
Subject: Re: [Discuss-gnuradio] XCRV2450 tx gain
Date: Mon, 22 Nov 2010 19:10:35 -0800


Look a little closer in the db_xcvr2450.cpp source. Both baseband and
VGA gain are implemented in the MAX2829. The gain specified in the UHD
block is independent of the transmit power amplifiers, which are always
enabled during transmit.


On Mon, 2010-11-22 at 23:16 +0100, Jorge Miguel wrote:
> Hi,
> I can see that the XCVR2450 allows to set a TX gain from 0dB to 30dB.
> I see in the XCVR2450 schematics that in the TX path path there is a
> MAXIM2829 chip (which has a programmable TX gain register from 0 to 64
> value) and then a power amplifier which amplifies 25-30dB (depending
> on the frequency band). I also see in the firmware of the UHD that the
> value set in software (from 0 to 30 dB) is not split between the MAX
> chip gain and a IRM046U7 Power amplifier.
> However I can see Ettus website that the XCVR2450 board in the
> transmit path has a gain of:
> VGA: 0-30 dB range
> BB: 0-5 dB range
> Is VGA gain the gain of the power amplifier and BB gain is the gain of
> the MAXIM chip? How are these two values set from the overall gain set
> in software (0 - 30 dB) ? It is not detailed in the firmware code. I
> need to understand where the 0 to 30 dB gain is psychically placed in
> the XCVR2450 (MAXIM or power amplifier)
> Many thanks,
> Jorge
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