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G8MNY > TECH 04.05.21 10:03l 45 Lines 1813 Bytes #999 (0) @ WW
BID : 32824_GB7CIP
Read: GUEST
Subj: Truth test for EMF Calculators
Path: IZ3LSV<DB0ERF<DB0RBS<OE5XBL<OE2XZR<OE6XPE<IW2OHX<UA6ADV<I0OJJ<GB7CIP
Sent: 210504/0851Z @:GB7CIP.#32.GBR.EURO #:32824 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (New Apr 21)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
Here is a simple exercise you can test an EMF calculator's grasp of reality.
Example 1, 400W to Example 2, 200W to
a Resonant Dipole. half of a Dipole
inverted L.
High
Current
Middle
ÄÄÄÄÄÄÄÄÄÄÄ¿ÚÄÄÄÄÄÄÄÄÄÄÄ High ÚÄÄÄÄÄÄÄÄÄÄÄ
High 200W ³³ 200W High current³ 200W 1 High
Voltage ³³ Voltage ³ Voltage
End 1 No Feeder End 2 coax===o)¿ End
Radiation ///
dBd gain = 0dB dBd gain = -3dB (-2.4dB?)
True ERP = 400W, Figure 8 pattern True ERP = 100W (150W), Omni pattern
The balanced feed represents no hazard, but the unbalanced feed wire against a
good ground is a problem until signal is in an unbalanced coax feed.
I am prity sure from first principles, that both of these aerials will have
the same high voltage at the ends (near field V/M field strength), but the true
ERPs are about 6dB different!
So for near field hazard results, both should produce the same safety distance
on a proper EMF safety near field calculator, but a 6dB difference (2x the
distance @ 400W) in far field non safety calculator.
Near field (transformer & capacitance effects) drops off at the cube of
distance rate (to 1/8 power @ 2x distance) for about the 1st wavelength or so,
then far fields @ square of distance (to 1/4 power for 2x distance) after that.
Why don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
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