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Here's the question I asked on Monday 5 June 1995:

Well, not actually from the headset, but from the resultant practice of keeping the HT with a quarter-wave antenna clipped to a belt in front or back of one's chest/abdomen. Since signals radiate outward, am I absorbing a lot more than if I held the HT to my ear and had the antenna way away from my head/body?

Should I build some sort of antenna-on-top-of-a-hat to (1) mitigate the RF I'm absorbing and maybe (2) increasing my range?

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Michael 'Mickey' Sattler     http://www.jungle.com/michael/ |
Digital Jungle Consulting Services           San Francisco, California |
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   Coordinator, Haight-Ashbury Neighborhood Emergency Response Team    |
 Bay to Breakers Red Cross Emergency Medical Technican/Communications  |
PADI Divemaster/Rescue Diver * KE6DZF * Bay Area Mountain Rescue Unit  |
 Macintosh bigot * mostly vegetarian * polyglot * ASL * owned by cat   |

From: Gary Coffman

Sure, but your trunk has a lot more wetted volume to absorb the power, and, unlike the skull, isn't resonant at VHF. The problem at the power level produced by HTs is the resonance effect on the skull, and the very sensitive to RF structures in the head, such as the eyes. Your body can easily absorb the 5 watts or so of RF heating, but your eyes can easily be damaged by heating at that level. So the idea is to keep the head and eyes as far from the source of RF as practical.

Belt mounting can do that, as can holding the HT at arm's length above the head while transmitting. Both tactics require an external microphone. The most damaging thing to do is to hold the HT in front of the lips to use the built in microphone. That places the antenna directly in line with, and very close to, the eyes.

Gary

-- 
Gary Coffman KE4ZV          |    You make it,     | gatech!wa4mei!ke4zv!gary
Destructive Testing Systems |    we break it.     | emory!kd4nc!ke4zv!gary 
534 Shannon Way             |    Guaranteed!      | gary@ke4zv.atl.ga.us
Lawrenceville, GA 30244     |                     | 

From: Edward Stafford

What multiple (including fractional) of two meters is your skull? The human body is pretty close to a whole wavelength. I do agree though that it is not a good idea to place an antenna so close to the head. I have always been amazed that people will use a clip to hold their rubber ducky on their hat. I think Darwin had something to say about that.

73s, Edward

From: Walter L. Zorn

Ed, et. al.,

RADIOFREQUENCY/MIRCOWAVE RADIATION THRESHOLD LIMIT VALUES (TLV) from the American Conference of Govenmental Industrial Hygienests (ACGIH), 1992. ISBN: 0-9367 12-99-6. On page 116, this document says (basically):

From 30 to 100 MHz there is a low with lead-in tapers from 3 to 30 Mhz (900/f**2) and lead-out tapers from 100 MHz to 1 GHz (f/100) for average power density. So, there is a reference that can be addressed. In this publication there are two notes of specific interest:

Note 1: "Needless exposure to all Radiofrequency Radiation (RFR) exposures should be avoided given the current state of knowledge in human effects, particularly nonthermal effects."

Note 4: "For partial body exposures at frequencies between 30 kHz and 1.0 GHz, the protection guides . . . may be exceeded if the output power of a radiating device is 7 watts or less. For example, if a hand-held transmitter operating at 27 MHz has a maximum output of 5 watts, it would be excluded from any further measurements."

Hummmmm. I guess we're to worry about this - unless we're CB'ers. But, operation above 100 MHz (2 meters) may be about the same as the region near 30 MHz (CB) - but, has an opposite slope. I know that's hard to understand without a picture, so:

Threashold Limit Values:

Average    100  __________\
Power                       \
Density     10                \                 /____________
(mW/cm**2)                      \           /
             1                    ________/


               30kHz     3 MHz   30MHz  100 MHz   1 GHz   300 GHz

I wish I understood all this. Anyway, what does this mean to me? I guess I'm concerned . . . I think of handheld antennas like a 5 watt "nightlight" (visual spectrum). I would not put a nightlight an inch from my eye for long durations. I also avoid staring at my rubber duck (except, when I'm not transitting and can't wait for a reply. Looking at the rubber duck at these times is like waiting for the pot to boil!)

"Blinded by the RF",
Walt / KF0OS

PS. Oh, what multiple (including fractional) of two meters is my skull? Geez. I measured and it seems to be about 7" (L), by 6 (W), by 5" (H). But the math for this big bald, kind-of round thing, is difficult - can you help me figure?

From: Doug

Yes your body absorbs quite a bit of the signal on your hip or chestpac. But most people don't leave them there all the time while communicating. The worst place is with the antenna next to your head RF Radiation wise. The signal gets out much better, but, your then zapping the RF into your temple area near you eyes. The higher in frequency you go the worse it gets, espically 1.2gHz radios. Would you stick you head in a micro wave oven?? Why then would you put the Radiation next to it? The safest way to emit signals with least amount of effect on the body is using a speaker mic so you can hold the radio about 2' away from yourself! This also improves the signal radiating out. Cheers Doug.

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*                     (ARS) KC6FRY  & Airedale Owner                     *
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Comments and views are strictly mine, and no way reflect the views of TRW.