Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!pacific.mps.ohio-state.edu!ohstpy!davis
From: DAVIS@ohstpy.mps.ohio-state.edu (JOHN E. DAVIS)
Newsgroups: sci.electronics
Subject: Re: How do I make a notch filter with cable?
Message-ID: <3070@ohstpy.mps.ohio-state.edu>
Date: 26 Jul 89 04:56:15 GMT
References: <4436@merlin.usc.edu> <29800@cci632.UUCP>
Distribution: na
Lines: 40

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...
>> 
>>          |<------------feed line cable length important??--------->|
>> 
>>          -----------------------------------------------------------
>> Antenna  ------------------------------+---------------------------- Receiver
>>          ----------------------------+ | +--------------------------
>>                               ^      | | | \
>>                               |      | | |  \ 
>>          The length of this   |      | | |   \___location of BNC "T" connector
>>          "stub" is cut to the |      | | |       important??
>>          wavelength of the    |      | | |
>>          offending frequency  |      | | |
>>                               v      |_|_| <---Short center conductor to shield
>> 
>> 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").
>> 
>> Has anyone heard of this before?  I know it's cheap and dirty, but I'm not sure
>> if the location of the "T" along the feedline is important.  There's no mention
>> of this kind of filter in the handbook, but I'm sure I've seen it before.

This is interesting. Can this type of filter be used to remove the
the "buzzing" sound and picture interference my cable company uses to 
scramble some of it's channels. Someone told me to use 300 ohm twin lead
and tin foil to do the job. Unfortunately I do not know the "scrambling
frequency" but I imagine it is somewhat standard.  


                                       Thanks
                                       John E. Davis
                                        OSU Physics