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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?
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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. -
Most likely it is not done through a hardware change, but through a software procedure after averaging the ADC samples.Comment
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The second stage feedforward resistor is switched:
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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.Comment
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It's just a binary-weighted network, nothing unusual. 2:1 ratios: 4k, 8k, 16k, 32k. It produces 16 different gains ( 24 ), one of which is 'all switches open', meaning 'Zero gain'.
If you want to replicate it with E24 resistors, use:
7k5; 15k; 30k; (30k+30k)
or:
(7k5//7k5); 7k5; 15k; 30kComment
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