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LF: Unwanted LF radiation

To: [email protected]
Subject: LF: Unwanted LF radiation
From: "Howard Aspinall" <[email protected]>
Date: Fri, 10 Jun 2005 11:27:03 +0100
Delivery-date: Fri, 10 Jun 2005 11:34:57 +0100
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This might be just a bit off the beaten track for the reflector, despite being 
LF orientated,
but I wonder if anyone has any useful observations or information they might 
pass on.

Whilst tracking down some noise interference problems, I discovered sizeable 
amounts
of wideband RF between 75 and 130 KHz. This manifests itself as
"smooth" noise. It extends outside these frequency parameters well into long/medium waveband, and is radiating from the overhead BT telephone drop line. Broadband internet RF seems the most likely culprit (there being a null between 130 and 140 KHz), but we do not have any broadband facility here.
An HP spectrum analyser close coupled to the line (common mode) shows this 
signal
level to reach at least 5 mV around 100 KHz.

Tests on BT lines in other areas where broadband is also not installed show no RF present other than broadcast stations etc.
Can anyone say if such common mode RF levels on BT lines can be typical, or might be
expected where no broadband facilities are connected? Are levels I am finding here
regarded as acceptable? And does anyone know of any regulations, codes of practice
or technical standards on the subject?
Howard   G3RXH









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