[R-390] Testing R-390 Mechanical Filters at a swap meet

[Tim Shoppa]

W7JPG asks:
> What is the "least complicated method"* to test a mechanical filter that is
> out of the receiver to determine if it is "good"**.

> What is the "absolute simplest and fastest method"** to test a mechanical
> filter that is out of the receiver to determine if there is a *high
> probability* it is "good"**.

Simplest is to ohm out the input and output coils and make sure they are not
open circuit.

Then make sure that neither input nor output coil is leaky to ground (again
an ohmmeter... a Megger on a lowish voltage setting if you have one.)

This does not test that the filter is a filter... it is simply checking that
over the years, the coils haven't opened up or shorted to developed leaks
to ground. But it will catch, in my experience, 100 percent of filter
failures.

Others have reported that the mechanics inside the filter can get
gummed up by the foam, and while my tests won't find gummed up
mechanicals, in at least some cases the gummy foam is responsible
for the leakage to ground.

Tim.