Re: Filter to remove AM radio from telephone lines
- From: macy@xxxxxxxxxxxxxx
- Date: 18 Jan 2007 09:38:16 -0800
mm wrote:
ALL Electronics sells DSL filters for around $3 apiece.
Thanks. I just noticed your post. I'm going to get one or two.
Jerry
The 'pigtail' type filters are only two wire connections for a singleFrom my experience:
phone line. If you use the other two wires, like a 2 line phone, they
don't work on that extra line
I've seen two types of pigtail filters: both cost around 10 to 12
1) simple single cap across the line - don't work well
2) common mode choke and cap - work very well
the choke looks like one of those 1/4 inch 600 ohm audio transformers,
actually has laminated core in it
Sometimes radio stations change their beam pattern to satisfy FCC
requirements. Depending on the time of day, you may see different
influences from that AM station. Like dusk, 6pm or so.
In Aptos, California near the 10KW AM radio station, the Station's
Engineer kindly supplied the excellent pigtail line filters to nearby
residents, who asked for them, at no charge, as a 'public relations
courtesy'
You mentioned that the effect gets worse with time OFF HOOK. Very
interesting, because ON HOOK you have high voltage and ON HOOK there is
lower voltage. Perhaps there is corrosion that is detecting the AM
signal.
Even using pigtails, keep in mind that *if* your lines are unbalanced,
the audio can get into them because the protection block is nonlinear
and detects AM. Once the audio is on your lines, it cannot be blocked
at any phone, because it is now legitimate audio.
- Robert -
.
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