[R-390] Filters

[Bob Camp]

Hi

If you are going to do an op amp filter, you need to do the math first. Op amps are fine for something that's 40 KHz wide and stable to a few KHz. One percent at 455 KHz is 4.5 KHz. The individual resonators in the 4 KHz filter are set up to within < 400 Hz of their desired frequency. 

Bob

On Feb 15, 2013, at 6:18 PM, quartz55 <quartz55 at hughes.net> wrote:

> Yes, I'm suprised no one has come up with a viable replacement myself after all this time, but hey.  I suggested an op amp filter, but it was poo-pooed at that freq, but with the new op amps we have these days, I wouldn't think 455 would be all that hard, but what do I know?  DSP would be too much of a project.
> 
> I'm sure the switch is fine, but it's really hard to tell with the filters in the circuit.  Now that they're out I'll check for sure, but everything except ohms to ground measures the same with a good IF module I have, and removing the 3 filters has raised the resistance to ground on the agc line on the IF with the bad filters.
> 
> I was measuring my filters with a Fluke 189.
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