Truth test for EMF Calculators
From
G8MNY@4:902/6 to
WW on Wed Dec 11 05:58:00 2024
To : TECH@WW
By G8MNY (Updated Jul 21)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
The new guidance limits originate from ICNRIP, for measurable body effects (often good for you, like hospital diathermal machines) & are many magnitudes below any serious safety limits! These limits have now been set into law for UK hams to comply with by UK regulator Ofcom.
Here is a simple exercise you can test an EMF calculator's grasp of reality. (EMF does not mean Electro Motive Force, as all engineers were taught, but now means Electro Magnetic Fields).
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.
From first principles, both of these aerials will have the same high voltage at their ends (near field V/M field strength), but the true ERPs are nearly 6dB different!
So for near field hazard results, both examples should produce the same caution distance on a proper EMF hazard near field calculator, but a 6dB difference (2x the distance @ 400W) in a FAR FIELD NON HAZARD calculator.
I always avoid the word "Safety" as the new regulations are based on "investigation levels" principles that "just might have a detectable effect on the body", & not actually "safety levels"!
N.B. Near fields (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
-----------------------------------------
ARGEN-X BBS - IPV6 TELNET LU9DCE.DYNU.COM -----------------------------------------
--- Mystic BBS v1.12 A48 (Linux/64)
* Origin: ARGEN-X BBS (4:902/6)