[R-390] R-390A Cost Reduction and Improvements (was dead horse Hi)

[John Kolb]

The mechanical filter could be replaced with a single IF
transformer or one or two tuned LC circuits, but the
overall bandwidth of that filter position will no longer
be 2, 4, 8 or 16 kHz with steep skirts. Instead, it will
be the overall selectivity of the replacement LC tuned
circuits plus the added rejection of the remaining IF
transformers in the set. It would take a number of hi-Q
tuned circuits to match the response of a 2 kHz mechanical
filter.

There may be a shortage of R-390A mechanical filters in the
Collins "N" case, but there's not a shortage of 455 kHz
mechanical filters - many flow past on that auction place.
Many could be adapted for use in the R-390A if one doesn't
need the replacement to fit within an "N" filter case.

Alternatively, a goo ceramic filter and matching circuitry
would fit inside a replacement filter case, and would give
a rounded top response rather than the rectangular top
of a mechanical filter, but could give a good shape factor.
(Wouldn't have the MF ringing either)

You can find a couple of R-390A filter plots as well as
some ceramic filter plots on my website,
<http://members.cts.com/king/j/jlkolb>

John

On Wed, 11 Jun 2003, Joe Foley wrote:

> Ok, so what's the recipe, ala R-390 style, for an LC
> filter?
>
> Can the R-390 filters be used in an R-390A?
>
> Or do we have to start from scratch, winding a coil
> shouldn't be too tough, selecting a cap to go with it
> should be easier.  Or do we have to have a tuneable
> cap for adjustment?  Would a slug tuned coil be
> better?
>
> Any ideas/possibilities for producing a short run of
> such a thing?
>
> Joe
>
>
>
>
> --- Todd Bigelow - PS <tbigelow@pop.state.vt.us>
> wrote:
> > Joe Foley wrote:
> >
> > >Has anyone ever tried to brew up a coil/capacitor
> > >replacement for the mechanical filters?
> > >
> > >
> > >Joe
> > >
> >
> > I seem to recall our pal Nolan posting something
> > about this. Maybe it
> > was Dr. Jerry, or a combination of both? It all came
> > from the
> > understanding that, eventually, all of the filters
> > would fail and we'd
> > need to figure out some way to
> > repair/replace/retrofit them.
> >
> > Might be something in the archives?
> >
> > ~ Boomer
> >
>
>
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