[RFI] NOISE GADGETS
David Jordan
wa3gin at erols.com
Thu Nov 11 07:57:15 EST 2004
I agree with Tom...his experience is that power line filters he has
tested make poor RFI fitlers. That is a fact of his experience.
My experience is different and I've been working in telco long before
the Internet and PCs when there was just one phone company...
But I have to tell ya Tom, my ISDN circuit ran error free with numerous
"power line" filters installed.
My conncection in the country is over 8 miles from the CO, all analog to
the switch. I consistantly get 28.8kbps connections, better than any of
my neighbors and yup, you guessed it, I've got a power line filter in
the line.
I'm just sharing my experience with the reflector Tom.
73,
dave
wa3gin
Tom Rauch wrote:
>>>The impedance of the wires has almost nothing to do with
>
> the
>
>>>design impedance of the system, because the wires are not
>>>large fractions of a wavelength long. The critical
>
> parameter
>
>>>is the source and load impedance. In a short line,
>
> standing
>
>>>waves have no place to stand.
>>
>>In a central office or studio, that's absolutely true. But
>
> if I'm miles of wire
>
>>from the central office it isn't.
>
>
> Central offices have little to do with it Jim.
>
> The signal is often in digital form over copper pairs, and
> is converted to analog at an equipment cluster near a
> distribution point. You can be 20 miles from the central
> office and have a 50-foot long analog pair, and your view of
> life will be that of someone 50 ft from the central office
> (unless you do a ping and echo test).
>
> My specific points in this are:
>
> 1.) Telephone systems are designed to be 600 ohms.
>
> 2.) It is impossible to predict characteristics of random
> power line filters, and how those filters will affect random
> systems
>
> 3.) Ability to survive poor balance and improper loading
> depends on what you run through the line and how far you are
> from the D/A conversion, which is almost NEVER at the
> central office.
>
> 4.) My experience, and I work on this stuff every week, is
> that power line filters make very poor telco RFI filters
>
> I can't add anything else to this topic.
>
> 73 Tom
>
>
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