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From: caesar@ge-dab.UUCP (Robert J. Caesar Jr.)
Newsgroups: net.analog,net.video
Subject: High-Q notch filter for cable TV signals
Message-ID: <394@ge-dab.UUCP>
Date: Thu, 9-Oct-86 08:53:44 EDT
Article-I.D.: ge-dab.394
Posted: Thu Oct  9 08:53:44 1986
Date-Received: Sat, 11-Oct-86 19:32:09 EDT
Organization: GE Simulation & Controls, Daytona Beach, FL
Lines: 25
Keywords: Coffee can, copper tubing, helical resonator
Xref: mnetor net.analog:869 net.video:2382

In order to eliminate the "objectionable noise" injected into some 
channels by the cable company,  Radio Electronics June issue suggests 
building a high-Q notch filter.

          "... An RF carrier can cause severe crosshatching.  Keying
           the carrier causes an annoying flicker, and the resultant 
           picture looks like a severe case of TVI caused by a CB or
           an amateur station.  In order to provide service to a 
           subscriber, a high-Q cavity notch filter can be made out
           of a coffee can and several feet of 1/8 inch copper tubing.
           Those materials can be used to construct a helical 
           resonator; tuning the resonator is merely a matter of
           adjusting its cavity of a notch at the interfering 
           frequency...."

Has anyone out there ever built one of these.  Any ideas on how it works?
Is the can common and the input/output taken off the tubing?  How might
one adjust the cavity of this high-tech device?


-- 
   Bob Caesar                   
   General Electric SCSD                      caesar@static.dab.ge.com 
   PO Box 2500 Room 4336                      (904) 258-3043 
   Daytona Beach, Florida 32015            ...!mcnc!ge-rtp!ge-dab!caesar