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Date: Sat, 20 Jul 91 10:00 PDT
From: John Higdon <>
Organization: Green Hills and Cows
Subject: Re: Serious RFI Problem

jonm@microsoft.UUCP (Jonathan MARK) writes:

> Certainly call the FCC -- they will send you a complaint form to fill
> out.  The radio station may be required to take measures to clean up
> their signal.  I get the impression that the FCC is pretty tough about
> this sort of thing.

The FCC will send you the standard sheet on how to RF-proof your
equipment. The assumption (and rightfully so) is that the station
involved is operating quite legally, within the terms of its license.
If you move into the near field of a station, it is NOT the station's
responsibility to redesign your substandard equipment so that it does
not receive RF. The FCC does not get "tough" with stations that are
simply carrying out their public trust.

There is a rule that requires NEW stations that begin or change
operations to solve "blanketing" problems within a one-mile radius of
the transmitter. They are required to do this for one year following
the commencement of operation. But existing stations are not required
to solve any and all RFI problems that occur every time someone new
moves into the near field.

A word of advice: many chief engineers are so bored with their jobs
that it would be a welcome challenge to help someone RF-proof some
equipment. This help could be invaluable and you should seek it out.
You will NOT get it if you come on as though the station "owes" it to
you. And more likely than not, a complaint to the FCC will not even be
forwarded to the station. If it is, then you may kiss off any free
help you might have received.

        John Higdon         |   P. O. Box 7648   |   +1 408 723 1395      | San Jose, CA 95150 |       M o o !

From: (Floyd Davidson)
Newsgroups: comp.dcom.modems
Subject: Re: Phone Line Impedance
Date: 7 Dec 1999 09:33:42 GMT

Henry Knoll  <> wrote:
>Does anyone know the typical phone line impedance at the phone?
>I want to design some RFI filters for my phones.

At voice frequencies, it is a nominal 600 ohms, but in fact the
line usually has a much lower impedance than that.  The
telephone instrument will be 600 ohms.

However it doesn't make any difference, relative to RF filters.
Neither the line nor the telephone set are specified at radio
frequencies.  And what you could see might be almost anything
from relatively low to several thousand ohms.

Unless you are dealing with VLF interference, the nominal
impedance of the telephone circuit will have little to
no influence on the filter, and visa versa.


Floyd L. Davidson                
Ukpeagvik (Barrow, Alaska)

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