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Date: Mon, 01 May 2006 13:09:58 +0200
From: Marek SQ5BPM <sq5bpm@wp.pl>
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To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
Subject: LF: EMF sensitivity?
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Dear LFers,

It happened to me for the 4th time. After long activity on LF I got a 
rash (or heat) on my face. Previously I related it to other things (like 
food, my dog etc.). Now, when I was inactive for months and it did not 
ever happen to me and after two days of activity I got it again, it 
seems to me it must be somehow connected with the LF transmitting. I 
suspect that this is due to one thing or everything connected, with 
decreasing order of probability:
- the loading coil, generating a strong field around it and being only 
less than 2m from me most of the time,
- air coils in final TX filter, which generate a wide range of spectrum 
from the incoming square wave,
- square switching of final FETs causing a few watts to be radiated in 
the VHF/UHF spectrum,
- the antenna itself, which starts indoors and goes up through the window,
- grounding wires which cause some energy to be radiated inside the club 
room as well.

The transmitter is in principle unshielded, only it's components are 
shielded against each other. The level of EMF in the club is noticeable, 
the 137kHz signal can be seen on CRT monitors as very subtle waves.

Strange, because apart from microwave burns I didn't know that such 
power levels (500W) can cause any visible effects. I've been working on 
HF for years, including participation in major RTTY contests for 48h 
with full legal power and never observed such an effect. FYI, I am 
generally not acquiring any allergies etc.

Has anybody seen that 'LF effect'? Or is that only my 'LF allergy'? ;)

Google found this: http://www.aehf.com/articles/em_sensitive.html - 
interesting, that skin effects appeared in the 20-50 kHz range.

73! Marek SQ5BPM