[R-390] Filter testing

[Bob Camp]

Hi

Even a simple 4:1 transformer will help you on the p-p voltage. You are close enough with the generator to your target 10V p-p for it to work. Of course 10V p-p is a very arbitrary goal. A lot depends on what your "detector" looks like. If your detector is a scope with a 5 mv / division sensitivity, two divisions would be 10 mv p-p. That would let you test things with 200 mv p-p input.

The resistance to ground is what's going to kill you. The way the AGC is set up you are in trouble with just about any measurable resistance to ground. There are various threads in the archives about rewiring this or that to get around  similar resistance to ground issues.   

Of course the old school approach to all this also still works. AM modulate the signal generator at 400 Hz. Use an AM radio with the AGC turned off as the detector. Measure the 400 Hz out of the radio with an AC voltmeter. Since you happen to have a 455 KHz AM radio sitting there….

Bob


On Feb 22, 2013, at 10:33 PM, quartz55 <quartz55 at hughes.net> wrote:

> Bob,
> Yes, and the function gen only goes to about 120K anyhow.  However, the R2005 service monitor I have does put out at least 4VP-P (it really only reads to 1V rms or 3.3VP-P out but cranks up a bit past that), so that may be good enough to work with. I'll just have to put a 100K resistor in series.  Plus it tunes in 10 Hz increments and is High Stab, so it's pretty accurate.   I'll give it a try tomorrow.  If I can get anywhere around .24VP-P out, the filter should be good, but I don't think it will be, because the resistance from the windings to ground is somewhere around 25Meg, much less than any of the others I have.  The foam has probably turned to sticky puckity and hopfully that will be an easy fix.
> 
> N3DT
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