Backpack antenna for 2m

[treod...@gmail.com]

I see a need for an antenna (hopefully made using 3/4 in tape measure) that would be attached to a backpack for use in assisting Search and Rescue personnel. In most cases the radio operator would be using an HT pushing 5-8 watts. I've considered a tape measure j-pole and a 1/2 wave dipole. I could see going with a longer vertical element and using a wire counterpoise "weaved" throughout the exterior of the backpack. If you will, think back to the antennas used with military's Man Portable radios such as the PRC77.

I'm open to any thoughts, advice, or "been there, done that" info.

Thank you,

KE5EXX

[Jeff Liebermann]

On Sun, 14 Aug 2016 16:52:01 -0700 (PDT), treod...@gmail.com wrote:

>I see a need for an antenna (hopefully made using 3/4 in tape measure)
>that would be attached to a backpack for use in assisting Search and
>Rescue personnel. In most cases the radio operator would be using an
>HT pushing 5-8 watts.

Ummm... 5-8 watts about 3 inches from the head does not sound
particularly safe.
<http://hintlink.com/power_density.htm>
8 watts, 2.2dBi gain, 0.5ft spacing, 146 MHz, and no ground
reflections yields 4.5mW/cm^2 power density. In an uncontrolled
environment, the limit it 0.2mW/cm^2, so you're over the limit by
quite a bit. You would need to be 2.4 ft away from the antenna to be
compliant with the MPE limits. Note that the FCC MPE limit does not
include exposure time, which will be rather small for your
application. Therefore you should be able to get away with such an
arrangement without frying anyone's brain. However, I think you can
do better with an antenna that extends over the users head, possible
with ground radials above the head to act as a shield.

Or, since there's a backpack involved, you might be able to obtain
some directional gain and shielding by simply putting a foil reflector
at the back of the backpack. The rest of the antenna will be a simple
1/2 wave dipole. If too big, a loaded half wave dipole, or undersized
dipole with a matching system, to reduce overall length. Antenna to
reflector spacing will be arbitrary but I suspect will produce some
kind of directional effect. I must admit that I've never built such a
contrivance, but offhand, it sounds feasible.

More ideas:
<https://www.google.com/search?q=vhf+backpack+antenna&tbm=isch>

Search and Rescue Radio Tracking
<http://www.sartrack.co.nz/>
<http://www.sartrack.co.nz/images/BackPackAntenna1.jpg>

Well, maybe not like this:
<https://s-media-cache-ak0.pinimg.com/564x/12/14/67/12146779db1f1fb22d5d6b4277d51eaf.jpg>


--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[Jeff Liebermann]

On Sun, 14 Aug 2016 19:52:36 -0700, Jeff Liebermann <je...@cruzio.com>
wrote:

More ideas...

HELP NEEDED: Design for a robust backpack-mounted 2m antenna
<https://www.zombiehunters.org/forum/viewtopic.php?f=42&t=74605>

2W/5W backpack COFDM wireless mobile video transmitter and receiver
<http://www.0086cctv.com/2w-5w-backpack-cofdm-wireless-mobile-video-transmitter-and-receiver>
<http://www.0086cctv.com/media/catalog/product/cache/1/thumbnail/9df78eab33525d08d6e5fb8d27136e95/d/s/dsc_0798_3__1.jpg>

[Wayne]

wrote in message
news:8a594c5a-79f3-4b46...@googlegroups.com...

Is this a "soft" backpack or a frame type with aluminum tubing and
compartments?

For the frame type, I've used a CB antenna mount designed for putting on a
side mirror.
The antenna was a whip with spring at the bottom.

Do the SAR folks wear protective head gear? I've seen metal hats that have
an antenna connector on top for a rubber duckie.