[RFI] Defibrillator and RF Exposure Query
jvpoll at dallas.net
Mon May 15 22:52:49 EDT 2006
----- Original Message -----
From: "Jim Brown" <jim at audiosystemsgroup.com>
To: "RFI List" <rfi at 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.
(2) ELECTROMAGNETIC RADIATION HAZARDS
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
More information about the RFI