Re: [Discuss-gnuradio] An analog RF question

[CEL]

Hi Marcus,

> Use digipots to set the R values, and use a fixed value for C, or
perhaps selectable C as well (probably only two or three values).

friends of mine tried to do variable attenuation for powerline
communication frontends using digipots, and: these can be very
frequency-selective, even below 10 MHz. Maybe they were just using the
wrong components.

> Or, a small number (4?) of selectable L-C-R low-pass filters, and fix the 
> sample rates to a small number.

That sounds like a nice choice, given the existence of highspeed analog
switches (which have gotten really affordable due to USB2, PCIe and
USB3).

I wonder if one could build an active filter with a (video?) opamp and
make components in the feedback branches exchangeable, assuming the
contribution of the analog switch compared to the effective component
values at the frequencies of interest are negligible. Then again, this
pretty much sounds like a non-integrated digipot, doesn't it?

Best regards,
Marcus

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