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Post Time: 20/03/2008 14:22:10 |
Jonny
Total Forum Posts: 7 |
It seems that the phone line can pick up and transmit other electromagnetic fields in the environment and these are experienced very unpleasantly by an electrosensitive using the phone. Do you know if and where I can get a filter that would block such fields? (I believe my old laptop had something similar - a thick plastic tube of about 3 cm in length that was part of the wire that went from the laptop to the electricity supply; it was located just a couple of centimetres along the wire before the plug that went into the back of the computer.)
Thank you
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Post Time: 04/04/2008 18:14:50 |
alasdairP
Total Forum Posts: 173 |
Jonny
I send my sincere apologies for the delay in our responding to your question. Yes, phone lines do pick up RF signals (especially if parts of their route are overhead on poles) and also all lines have now some ADSL broadband signals on them, even if you do not subscribe to telephone line broadband. The unrequested ADSL signal levels can be quite high.
So, the first thing to do is to install a plug-in ADSL line filter between the line and each telephone that you have. These only cost a few pounds, now. There are some neat ones here (www.rwapsoftware.co.uk/filters.html), but any computer shop or COMET or Currys or Argos etc will usually have them under 10 GBpounds.
BT sell their ADSL Micro Filter MF50 (or 4D46WS)for 7 GBP. You may find using two in series works even better as then you have an HF extra filter stage that should not affect your phone's working as UK spec is for about 32dB attenuation (1000-fold signal power reduction) from 30 to 300 kHz and some countries allow two-stage filters for 60+dB (1000,000-fold signal power reduction) and two filters in series should give you this in the UK.
Secondly, you can add one or more clamp-on ferrite filters such as you describe. EMFields actually stocks and sells one type that is suitable. Scroll down the following page to "Ferrites". These ones have a 6mm hole so that you can wrap a loop of your telephone cable back through the ferrite before closing the clamp and that makes it even more effective at stopping very high frequencies travelling along the cable. They cost GBPounds 4.59 each from EMFields.
( www.emfields.org/screening/overview.asp ).
If doing both those things doesn't stop enough then further filtering is possible but gets much more complex and expensive, especially if you are not into self-build electronics. However, for most sensitive people those actions together should be adequate. They will reduce the HF noise by a very large amount (difficult to put a figure without measuring because of local differences, but should be a very great reduction).
Alasdair
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