> -Original Message-
> From: Repeater-Builder@yahoogroups.com [mailto:Repeater-
> [EMAIL PROTECTED] On Behalf Of Jeff DePolo
> Sent: Monday, January 14, 2008 11:21 AM
> To: Repeater-Builder@yahoogroups.com
> Subject: RE: [Repeater-Builder] Revisiting Shor
> -Original Message-
> From: Repeater-Builder@yahoogroups.com
> [mailto:[EMAIL PROTECTED] On Behalf Of Paul Plack
> Sent: Sunday, January 13, 2008 6:22 PM
> To: Repeater-Builder@yahoogroups.com
> Subject: Re: [Repeater-Builder] Revisiting Shorted 1/2-wave
> Paul,
>
> Curious who makes the RG-8M you have.
Jeff, the cable is Tandy. In the '80's, the Tandy Wire & Cable RG-8M was much
better than their own full-sized RG-8, and they'd sell you 20' off the roll at
the store. I used it in many mobile installations when there wasn't time to
mail-order s
Jeff: please sweep the other stubs you mentioned, so
we have something for comparison. Might as well do all
the varieties possible, and tabulate the results at
both 900 and the FM band.
Considering how easy it is to make such traps, perhaps
a short article could come out of it? You could add it
to
> My coax is RG-8M, similar to RG-8X. I couldn't find a
> published velocity factor for M, but thought I remembered
> .87. RG-8X is .84 (not .66). I cut a piece off an old scrap
> cable (with connector) to 41 inches, measured from the tip of
> the PL-259's center pin to the cut point, as a st
Guys, I appreciate the thoughtful responses. I've been taught the same stuff
about impredance transformation vs. electrical length, but I've also seen these
traps work.
Gary wrote: "This measurement that you made indicates that the cable is a
quarter wave (not ½ wave) at 146.15 if indeed you do
> One of the initial proposals
> was an open, 1/4-wave stub tuned for the FM broadcast
> frequency, fed on a coaxial T-connector. This is, indeed, a
> common method to "trap" a particular frequency.
>
> I set forth that this wouldn't work, as the desired pass
> frequency was too near the 9th h
Paul, I think where the problem with your measurements comes up is that your 41
inches of RG-8 is close to 3/4 wave at 2 meters, not 1/2 wave. Taking a rough
estimate of 19 inches for a quarter wave on 2 meters (the approximate length of
your quarter wave ground plane vertical element) you woul
will see the short
though.
73
Gary K4FMX
_
From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Paul Plack
Sent: Sunday, January 13, 2008 1:57 AM
To: Repeater-Builder@yahoogroups.com
Subject: [Repeater-Builder] Revisiting Shorted 1/2-wave Traps
I'm posting this with all due respect to those who disagreed with an earlier
post, and in the hopes of discovering any error I might be perpetuating.
A few weeks ago, a member of the group was asking for help with interference on
the input of a 900-MHz ham repeater from a co-located FM broadcast
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