All is not lost Josh - I'm running Motorola T1507 which are 4-can
pass-only cavities on my Micor. Actually pass-only are better for
commercial sites since they will help keep out a lot of intermod on
either side of how they are tuned.
Pass-notch on the other hand will pass the tuned frequency, but do a
poor job of "everything else" rejection (other than the notch of course).
On 05/29/2010 08:27 PM, Josh wrote:
Certainly not what I was expecting... Yeah, I bought one from 'that
guy'. It's more than an untrained eye - he straight lied to me... said
'under these caps are where you'll tune the capacitors' - I should
have popped one off and looked down the hole. Maybe he was clued in,
maybe he wasnt - either way, that's what I bought. Dangit :P
So if all I have are pass cavities.... what 'are' they good for ?
Guess I've got to find another dupelxer.
j
--- In [email protected]
<mailto:Repeater-Builder%40yahoogroups.com>, "Jeff DePolo" <j...@...>
wrote:
>
> > Ok so here's what I've got (I think)
> >
> > http://www.n2ckh.com/FORSALE/REPEATERS/DUPLEXERS/DB4076/DSC02678.JPG
> >
> > Hamvention special, 4 cavities, appears to be a DB Products
> > 4076 family unit. My bench tools: HP 8924c w/ Spec Analyzer
> > and Tracking Generator.
>
> There was a guy at the Hamvention that had several sets of Decibel
> four-cavity window filters, selling for $50 each, which, to the
untrained
> eye, would look like an older DB4076. As you said, there would be
nothing
> in the hole where the capacitor would be in a regular DB4076. In
essecence,
> what you have are just plain-jane pass cavities.
>
> As a second means of confirming that you do, in fact, have a window
filter,
> is there an antenna "tee", or are the four cavities cabled together in
> cascade? If the latter, then you probably have a window filter.
>
> And as a third means of confirming, is there is a label on the front? If
> not, was there any signs of a label having once been there? If not, then
> that's yet one more indication that it isn't a DB4076.
>
> Decibel made two varieties of pass cavities used in window filters
in that
> era. One had adjustable loops (less common), the other had fixed
loops. If
> your loop connectors have a rectangular chrome plate around them with
> insertion loss calibration marks, you have the less-common
adjustable ones.
> If you just see four philips-head screws and no chromed plate around the
> connectors, then yours is not adjustable.
>
> If you have the adjustable type, you could probably use them as a
pass-only
> duplexer, but with mediocre isolation, even with the insertion loss
cranked
> up higher than you'd like. If you have the non-adjustable ones, they
have
> very tight coupling, so you're not going to get the isolation you'd
need for
> a repeater.
>
> > Did I buy a piece of junkola? Teach me obie-wan.
>
> Not junk, but maybe not what you were expecting...
>
> --- Jeff WN3A
>
