Yes, they did sell window filter as a separate catalog item, but if they
were sold as such they would have had a factory sticker on it. The ones I
have don't have a sticker, which is why I said they were probably part of a
package that would likely have had an SP part number rather than a DBxxxx.
These cavities are very tightly coupled, typically about 0.3 dB or so
insertion loss per cavity. Strung together, the total insertion loss is
about 1.5 dB. Because of the coupling, each cavity individually doesn't
have a very high Q, so if you were to take one of these units and "split" it
to try to make a duplexer out of it, you'd probably only get about 40 dB or
so of isolation at 5 MHz offset. Even if you did want to try it, you'd have
to change cable lengths to get the pass response of each cavity to add
on-frequency rather than creating a wide window filter passband as they were
originally cabled.
They do tune fine down to 440 as-is (i.e. as a window filter).
--- Jeff
> -----Original Message-----
> From: Repeater-Builder@yahoogroups.com
> [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Eric Lemmon
> Sent: Monday, May 31, 2010 12:52 PM
> To: Repeater-Builder@yahoogroups.com
> Subject: RE: [Repeater-Builder] Re: Help Needed (Guidance and
> advice) tuning a DB Products Duplexer
>
>
>
> Not really. I had not seen this in any of my older catalogs,
> and I wondered
> if in fact the unit was made by Decibel Products. Like many
> RF products,
> ferrite isolators in particular, the frequency range stated in a
> manufacturer's catalog refers to the capability to construct-
> which is not
> the same as the field-tunable range of a specific product. I
> was curious if
> the window filter (AKA preselector) could be useful in the 70
> cm Amateur
> band without modifying the coupling loops or jumper cables.
>
> 73, Eric Lemmon WB6FLY
>
>
> -----Original Message-----
> From: Repeater-Builder@yahoogroups.com
> <mailto:Repeater-Builder%40yahoogroups.com>
> [mailto:Repeater-Builder@yahoogroups.com
> <mailto:Repeater-Builder%40yahoogroups.com> ] On Behalf Of Jeff DePolo
> Sent: Monday, May 31, 2010 6:09 AM
> To: Repeater-Builder@yahoogroups.com
> <mailto:Repeater-Builder%40yahoogroups.com>
> Subject: RE: [Repeater-Builder] Re: Help Needed (Guidance and
> advice) tuning
> a DB Products Duplexer
>
> Mine don't have labels on them. Usually they were sold as
> part of an SP
> package that included the window filters, multicoupler, etc.
>
> I haven't tuned or swept this particular set, but from experience, the
> cavity resonance will tune over a wide swath, probably the
> full 406-512 MHz,
> but the loop lengths may not be optimal over such a wide span
> (depending on
> how the cavities are being used), and likewise, the cable
> lengths will vary.
>
> You have something in particular in mind you want me to test?
>
> --- Jeff WN3A
>
> > -----Original Message-----
> > From: Repeater-Builder@yahoogroups.com
> <mailto:Repeater-Builder%40yahoogroups.com>
> <mailto:Repeater-Builder%40yahoogroups.com>
> > [mailto:Repeater-Builder@yahoogroups.com
> <mailto:Repeater-Builder%40yahoogroups.com>
> <mailto:Repeater-Builder%40yahoogroups.com> ] On Behalf Of Eric Lemmon
> > Sent: Sunday, May 30, 2010 12:29 PM
> > To: Repeater-Builder@yahoogroups.com
> <mailto:Repeater-Builder%40yahoogroups.com>
> <mailto:Repeater-Builder%40yahoogroups.com>
> > Subject: RE: [Repeater-Builder] Re: Help Needed (Guidance and
> > advice) tuning a DB Products Duplexer
> >
> >
> >
> > Jeff,
> >
> > Can you positively identify the window filters by part
> > number? Also, what
> > is the useful frequency range of the units you purchased?
> >
> > 73, Eric Lemmon WB6FLY
> >
> > -----Original Message-----
> > From: Repeater-Builder@yahoogroups.com
> <mailto:Repeater-Builder%40yahoogroups.com>
> <mailto:Repeater-Builder%40yahoogroups.com>
> > <mailto:Repeater-Builder%40yahoogroups.com>
> > [mailto:Repeater-Builder@yahoogroups.com
> <mailto:Repeater-Builder%40yahoogroups.com>
> <mailto:Repeater-Builder%40yahoogroups.com>
> > <mailto:Repeater-Builder%40yahoogroups.com> ] On Behalf Of
> Jeff DePolo
> > Sent: Sunday, May 30, 2010 8:39 AM
> > To: Repeater-Builder@yahoogroups.com
> <mailto:Repeater-Builder%40yahoogroups.com>
> <mailto:Repeater-Builder%40yahoogroups.com>
> > <mailto:Repeater-Builder%40yahoogroups.com>
> > Subject: RE: [Repeater-Builder] Re: Help Needed (Guidance and
> > advice) tuning
> > a DB Products Duplexer
> >
> > <snip>
> >
> > I bought two sets of those window filters from the same guy,
> > but I knew what
> > they were, caveat emptor is the golden rule at Dayton or any
> > other hamfest.
> > Actually I think I gave him $75 for the pair, and I took the two
> > cleanest/newest ones he had (the newer dark-tan ones).
> >
> > --- Jeff WN3A
> >
> > <snip>
> >
> >
> >
> >
> >
>
>
>
>
>
