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[aprssig] Helmet Antenna - dont bother.

Robert Bruninga bruninga at usna.edu
Mon Mar 7 14:23:14 UTC 2005


Geeze, which is better.
5W radiating into your face from an HT or 5W
radiating above your head with your head inside
below a ground plane?   Or are you saying dont
use a radio at all.  Its too dangerous...?        Bob

>>> k4gps at arrl.net 3/6/05 8:49:50 PM >>>
Bob... I hate to preach but let me see here you have a 1/4 wave
antenna
right at the VHF frequencies somewhere near 1/2inch or less from your
head
at 5W.
Foil or no foil Bob please do yourself and your family a favor don't
take
the risk however small it is. I have not taught RF Safety in several
years
but take a look at some of the ARRL Tech License publications, they
point
out several things about VHF vs. Microwave and how many people are so
much
more afraid of MW than VHF and it should be the other way around.

That is not something I would be mentioning out in public. Actually for
some
time I saw a lot of geeky hard hats with BNC connectors on the top of
them
sold at hamfests, I think everyone got the message long ago since I no
longer see them for sale.

Rich



-----Original Message-----
From: aprssig-bounces at lists.tapr.org 
[mailto:aprssig-bounces at lists.tapr.org]On Behalf Of Robert Bruninga
Sent: Sunday, March 06, 2005 7:25 PM
To: aprssig at lists.tapr.org 
Subject: [aprssig] Helmet Antenna - dont bother.


Today I was tail-bike on a marathon.
Lesson:  Dont bother with a helmet antenna
for voice.  (APRS maybe, but not for just voice).

I took one of those tiny 19" mag mount
whips with a small base (like a kisses chocolate piece)
stuck it inside the helmet protruding up through the
air holes, covered the inside with aluminum foil and
then let a can lid stick to the bottom of the magnet.

I also, carried an identical HT with its own
long whip.  Conclusion was generally no difference
after lots of side-by-side tests...
Therefore, dont bother.

An HT held to my mouth with a similar 19" whip is
going to work similarly as a 19" whip on the helmet at
the same height.  I had just hoped that the slightly
better ground  plane might work better than the HT with
no real  counterpoise.... dont bother.

Now, for APRS where you are not holding the HT to
your mouth, then maybe the extra height and lack
of body blockage is worth it.

Just 2 cents...
Bob



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