I would add, put a 300-Ohm high pass filter between the
two 75/300 Ohm transformers.
Most TV's, especially those manufactured prior to 1982, have
no shielding against direct pick-up (which would also affect fundamental
overload). There's little you can do, but just be aware of this.
Many aftermarket TV amplifiers, especially those available in supermarkets
and Joe's TV, are poorly made and shielded. If you or the neighbor uses one,
ask the cable company for one as they are usually of better quality.
73,
Bob AA0CY
----------
From: Blackburn[SMTP:blackburn@QNET.COM]
Sent: Wednesday, December 22, 1999 8:49 PM
To: rfi@contesting.com
Subject: Re: [RFI] Phone RFI fixes - no ring, lower cost solutions?
For some reason this didn't get posted...let's try it again.
Keith
Blackburn wrote:
>
> George,
>
> A couple more thoughts to try. The last house I lived in (abt 8 yrs
> ago) that had cable TV also had TVI problems with nothing more than 100
> watts & a dipole.
>
> 1. Make sure that all the cable connectors and any connectors going to
> splitters, etc., are in good shape, securely crimped onto the coax, and
> securely tightened, and that any unused splitter ports are capped. I
> fixed one TVI problem while in the process of tracking down loose
> connections by nothing more than disconnecting & re-connecting a splice
> in the cable (obviously had a poor shield connection).
>
> 2. Most TV's I have encountered (including both that I currently own)
> respond to relatively low-level common-mode HF signals on the antenna
> lines. An easy way to break the common mode path is to go to Radio
> Shack, buy a couple of 75 ohm - 300 ohm transformers, connect the 300
> ohm sides together, and install the pair in line with the cable coax at
> the back of your TV. Check the transformers with an ohmmeter to make
> sure there isn't a DC connection between the 75 and 300 ohm sides. This
> arrangement breaks the common-mode path while still passing the intended
> (differential mode) TV signals.
>
> Agree that a high-pass filter probably wouldn't do much to eliminate HF
> TVI...
>
> Gud luck & 73,
>
> Keith
> KB6B
>
> Jon Ogden wrote:
> >
> > on 12/21/99 7:47 PM, Gorsline Family at gorslin@pathcom.com wrote:
> >
> > > Ideally, I'd like to give the neighbours the plug-in modular filters -
> > > enough for every phone (say 5/house). At $30-40 CDN each, is there a
> > > less expensive way?
> >
> > Rich Measures, AG6K, has plans for homebrew phone filters on his website.
> > They are basically the same as what you would pay big bucks for. The URL
> > is: http://www.vcnet.com/~measures/T.RFI.html and
> > http://www.vcnet.com/~measures/phone.fil.GIF
> >
> > Hopefully that can help.
> >
> > >
> > > For the TVI - is there a high pass coax filter (ideally male-female to
> > > put in the CATV line)? Yes, lots of cable ingress/egress - 2m and CATV
> > > channel 18, pagers on channel 17 and 21.
> >
> > If you are having cable ingress, contact your local cable company. They are
> > responsible for leakage into as well as out of their system. If pagers are
> > getting in then lots of people have complaints and not just your neighbors.
> > The FCC holds the cable company responsible. Realize that if you are other
> > services are getting IN, then they are radiating signal which means, the
> > CATV will likely be interfering with YOU somewhere.
> >
> > If there is fundamental frequency ingress, filters won't help one bit. If
> > any of your VHF/UHF signals are getting into your CATV channels, then it
> > won't help to put a filter in line since your frequency and perhaps the CATV
> > channel frequency are the same. The only way to stop it is to make the
> > cable company close their system, which it should be.
> >
> > Hope this helps.
> >
> > 73,
> >
> > Jon
> > KE9NA
> > --
> > -------------------------------------
> > Jon Ogden
> > KE9NA
> >
> > http://www.qsl.net/ke9na
> >
> > "A life lived in fear is a life half lived."
> >
> > --
> > Submissions: rfi@contesting.com
> > Administrative requests: rfi-REQUEST@contesting.com
> > WWW: http://www.contesting.com/rfi-faq.html
> > Questions: owner-rfi@contesting.com
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