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Re: [RFI] Defibrillator and RF Exposure Query

To: "Jim Brown" <jim@audiosystemsgroup.com>,"RFI List" <rfi@contesting.com>
Subject: Re: [RFI] Defibrillator and RF Exposure Query
From: "Jim P" <jvpoll@dallas.net>
Date: Mon, 15 May 2006 21:52:49 -0500
List-post: <mailto:rfi@contesting.com>
----- Original Message ----- 
From: "Jim Brown" <jim@audiosystemsgroup.com>
To: "RFI List" <rfi@contesting.com>
Sent: Sunday, May 14, 2006 10:38 PM
Subject: Re: [RFI] Defibrillator and RF Exposure Query

> On Sat, 13 May 2006 23:05:11 -0500, Jim P wrote:
> >Maybe I'm missing something in regards to the caveat: "and 
> operate 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 

I think you're overlooking something here Jim, vis-a-vis near-field
versus far-field effects (1) as presented by an excited antenna. 

The effects which I am addressing are the strong non-radiated 
'fields' an antenna exhibits as opposd to the radiated 'wave' it 
creates and one experiences at a distance from said transmitting 
antenna; 'fields and wave's: there is a difference (3).

Take and consider for a moment the high voltage E-field as well
as the strong H-field in the proximity of an excited dipole (2) - 
THESE are the effects are seen close in to a transmitting antenna
and the effect one experiences with an 80 M dipole strung between
two trees over a house.

Currents LARGER than those seen due to the simple reception of
a signal from a distance can be made to to flow in a device in
the near-field *owing to* displacement currents created by the 
effects of capacitive coupling from the high RF voltages present 
in the near field ... no?

The 'Simple Proof':  Ever see the demonstration where a nominal 
3.5 Watt Class D 27 MHz radio 'fires' an NE-2 Neon lamp with 
a  65 V ionization voltage (between electrodes) when held near 
the end of a 9' whip while said rig transmits?

Again, the effects you seem to keep alluding to are the *far-field* 
effects, i.e. the effects as seen along the lines of a wavelength 
and more (1). 

SO, with all this in mind, let us again consider the wavelength of  
an 80 Meter signal (260') and how far away the aforementioned 
E and H 'fields' exist knowing the wavelength of said 80 M signal
(around 260'), and furthermore, that these fields will be seen 
and experienced by equipment and to a lesser degree by per-
sonnel present in said antenna's 'near field'. 

Jim P  //  WB5WPA  //


(1) Near field or far field?

Copyright fair-use excerpt:

  "Because the far field exists, logic suggests the 
   existence of a close, or near, field. The terms "far field" 
   and "near field" describe the fields around an antenna 
   or, more generally, any electromagnetic-radiation source. 
   The names imply that two regions with a boundary be-
   tween them exist around an antenna. ...

   These boundaries are not fixed in space. Instead, the 
   boundaries move closer to or farther from an antenna, 
   depending on both the radiation frequency and the amount 
   of error an application can tolerate. 


Copyright fair-use excerpt:

  "Although E-Field, H-Field, and power density can be 
   mathematically converted in a far-field plane wave environ-
   ment, the relations provided earlier do not apply in the 
   near field, consequently the E- or H-field strength must 
   be measured independently below 100 MHz."

(3) Fields and Waves Demonstrations

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