Path: utzoo!attcan!uunet!cs.utexas.edu!sun-barr!decwrl!ucbvax!bloom-beacon!mit-eddie!genrad!decvax!ima!mirror!frog!john
From: john@frog.UUCP (John Woods)
Newsgroups: sci.electronics
Subject: Re: How do I make a notch filter with cable?
Keywords: filter, notch, cable, short, simple, hi-Q
Message-ID: <1681@frog.UUCP>
Date: 24 Jul 89 22:24:00 GMT
References: <4436@merlin.usc.edu> <29800@cci632.UUCP>
Distribution: na
Organization: Misanthropes-R-Us
Lines: 30

In article <29800@cci632.UUCP>, dvh@cci632.UUCP (David Hallidy) writes:
> In article <4436@merlin.usc.edu>, cyamamot@nunki.usc.edu (Cliff Yamamoto) writes:
> > Greetings,
> > 	I am trying to make a sharp notch filter to cut out an overbearing
> > paging transmitter that swamps my PRO-2004 scanner on the VHF bands.  I
> > *think* I've read somewhere before about how one can cut a piece of cable
> > to a certain length and short it at the end to kill the frequency of said
> > wavelength.  Something like this...
> > The pager frequency is 152.4 Mhz.  So using the ol' ARRL handbook I get a
> > wavelength of 1.96 meters (length of the "stub").

This may not be a practical solution to your problem, but it's an interesting
one:  some years back in QST magazine (probably between '76 and '78) someone
had an article about a 2-meter (~146Mhz) resonator used for allowing two
stations to share the same antenna (during contests, I believe).  The author
had discovered that a standard 55-gallon garbage can was very close to being
a resonant cavity for that band, requiring only a modest (adjustable) 2-plate
capacitor in the middle (which was large enough that hot dogs could be
rested on it and heated while transmitting (with a little retuning,
of course)).  If you can dig up the article, and if it appeals to you, you
might be able to get away with it for this application.  Just think -- someone
comes in to your den, sees a garbage can, asks you what it is, and you can
reply, "Oh, that's where I throw away unwanted signals from pagers."

John Woods, WB7EEL/1
-- 
John Woods, Charles River Data Systems, Framingham MA, (508) 626-1101
...!decvax!frog!john, john@frog.UUCP, ...!mit-eddie!jfw, jfw@eddie.mit.edu
    People...How you gonna FIGURE 'em?
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