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[aprssig] Helmet Antenna - dont bother.

Rich Garcia k4gps at arrl.net
Mon Mar 7 05:06:27 UTC 2005


Yes..I have noticed that along with Yaseu doing the same for their 1.2Ghz HT
many years ago.
I believe it is the same product that is sold in many Asian countries where
1.2 and above
abound but it seems that even with current production 1.2 and above
equipment is rarely
imported even in small or by special order.

As far as the 2M HT A.J. yes you are correct there is no difference and it
should be treated
with great respect. Proper knowledge is a powerful thing, I had a lot of
concerns for my wife
who worked for several years in a Heart Cath lab and was exposed not only to
several types of
radioactive materials but also to constant X-Rays while in the room with the
patient. They have
the protective gear and the proper training and Dosimeters so they have the
knowledge to work
with it 40+ hours a week.

Same goes with a HT, knowing what we should all know now that it is part of
the FCC rules we should
be more careful with a VHF HT than what some think would be worse a UHF HT.
I remember that the human body will
resonate both at 27Mhz with another smaller peak in the VHF Commercia/Marine
band from the charts in ARRL
publications.

How can we still enjoy the hobby as we know it ? By reducing the duty cycle
which would lower our MPE, reducing the power,
and placing as much distance between our body and antenna as we can possibly
do. Meaning use a external
antenna if we use a HT, or avoid gain antennas on VHF since that will
increase your ERP, and if all of
that is not possible keep the transmissions as short as possibe, any or all
of the above will help.

Packets are short, so OK the MPE may have not been reached for a small bike
ride but if someone does this
all the time, for long marathons or heck for commuting to work or school I
would worry. It's not the
first time of a HT worry, the NYCTA (Transit Authority) PBA first brought up
the concern due to concern for
eye damage with their "New 800 Mhz" radios, this was a long time ago. Due to
these PBA studies and concerns
the union was able to make a valid point and then I think Motorola started
making the Elevated Feed Rubber Duck,
these were used both on the HT's and/or the shoulder mic's that had antennas
mounted on them so that the 1/4w
element was not level with the retna. Now that I think of it same style of
antenna came with the Motorola "Brick
Phones" that were popular well into the late 90's.

Rich

-----Original Message-----
From: aprssig-bounces at lists.tapr.org
[mailto:aprssig-bounces at lists.tapr.org]On Behalf Of Ian
Sent: Sunday, March 06, 2005 10:06 PM
To: 'TAPR APRS Mailing List'
Subject: RE: [aprssig] Helmet Antenna - dont bother.


Icom's T-81A quietly disappeared even though it was the only game in town
for 1.2GHz HTs. Some lawyer must have advised Icom after figuring out that
our eyes resonate just below 23cm that this was product liability in the
making.

73 de Ian
N8IK

-----Original Message-----
From: aprssig-bounces at lists.tapr.org [mailto:aprssig-bounces at lists.tapr.org]
On Behalf Of Gerry Creager N5JXS
Sent: Sunday, March 06, 2005 9:25 PM
To: TAPR APRS Mailing List
Subject: Re: [aprssig] Helmet Antenna - dont bother.

Simply put, Rich's comments are on-target.  HT's are made the way they
are for convenience and tradition.  That they're not the safest
configurations in the world isn't a major concern to the radio
manufacturers.

A.J. Farmer (AJ3U) wrote:
> When you hold an HT up to to talk, you have the antenna right in front of
> your face and close to your head.  What's the difference?
>
> -----Original Message-----
> From: aprssig-bounces at lists.tapr.org
[mailto:aprssig-bounces at lists.tapr.org]
> On Behalf Of Rich Garcia
> Sent: Sunday, March 06, 2005 8:50 PM
> To: TAPR APRS Mailing List
> Subject: RE: [aprssig] Helmet Antenna - dont bother.
>
> 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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--
Gerry Creager -- gerry.creager at tamu.edu
Texas Mesonet -- AATLT, Texas A&M University
Cell: 979.229.5301 Office: 979.458.4020 FAX: 979.847.8578
Page: 979.228.0173
Office: 903A Eller Bldg, TAMU, College Station, TX 77843

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