[R-390] filters

[Cecil]

We know there is some kind of foam material in them that turns to gum that impedes propagation through the filter that probably accounts for the filter loss seen in these aging filters.  There have been those that have opened them up..cleaned them out and replaced the foam with some positive results.

I guess we had get good at this since that is where they all are heading unless we find a suitable replacement.

Cecil

Sent from my iPad

On Feb 7, 2013, at 5:45 AM, Bob Camp <ham at kb8tq.com> wrote:

> Hi
> 
> The mechanical filters are made up of resonators. They work by acoustic resonance. You need to be very careful about how you mount them.
> 
> Bob
> KB8TQ
> 
> On Feb 6, 2013, at 9:31 PM, John Wendler <wendlerjrv at gmail.com> wrote:
> 
>> Would any of the knowledgeable folk on the list care to comment about the
>> donut material and whether the old material was chosen as an acoustic
>> isolator to prevent microphonics?
>> 
>> 73 de John, N5CQU
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