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Re: [RFI] Defibrillator and RF Exposure Query

To: "RFI List" <rfi@contesting.com>
Subject: Re: [RFI] Defibrillator and RF Exposure Query
From: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Sun, 14 May 2006 20:38:38 -0700
List-post: <mailto:rfi@contesting.com>
On Sat, 13 May 2006 23:05:11 -0500, Jim P wrote:

>Maybe I'm missing something in regards to the caveat: "and 
>on the lower HF bands".

The receiving antenna (within the subject wired with the 
electronic device) needs to be a significant fraction of a 
wavelength to receive significant voltage from the transmitting 
antenna. So, all things being equal (distance, power, etc.) lower 
frequencies will induce less current in the human body than higher 
ones by virtue of the electrical length of the receiving antenna 
(the human body). 

Example -- LF and VLF broadcast stations transmit with 
considerable power (100 kW to 2 MW), but RFI from these stations 
to audio equipment is almost unheard of. Why? The receiving 
antennas are FAR too short as a fraction of a wavelength at these 
frequencies to be efficient receiving antennas. 

Remember, I'm assuming an HF transmitting antenna that may be 
wires or a vertical of some sort, and thus potentially close to 
the subject, which is what the original post described.  I know 
this setup well -- I lived with it at the QTH that I just moved 
away from (see the link on qrz.com to my website). 


Jim K9YC

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