Adjustable gain pre-amp

[Repwoc]

In this (rather old) video on the White's V3i the presenter shows (0:20) how to set the Rx gain - the setting is 1 - 15 where 1 is low gain and 15 high gain. Does anyone know how this was achieved with the V3i? I guess it was probably a system of switching different resistors in and out to change an op-amp gain, but maybe there's a better way?

[Altra]

Not sure how the V3 did it? The MXT used a CD4051 to switch resistors in the pre-amp. Today we have programable gain amplifiers (PGA), one example is the MCP6S22.

[boilcoil]

Most likely it is not done through a hardware change, but through a software procedure after averaging the ADC samples.

[Carl-NC]

The second stage feedforward resistor is switched:

[boilcoil]

Thanks, Carl.

[Repwoc]

Yes, thanks Carl. It must have taken a while to figure out all the resistor values to produce 15 total gains (stage 1 * stage 2) ranging from ~22 to ~330 all evenly spaced by ~22.