[caption id="attachment_1055" align="alignleft" width="169"] Fiberglass mast
with two VHF j-pole antennas affixed.[/caption]
I recently started working with Calvert K9
Search, a local
SAR team that
specializes in using dogs to search for people. In an effort to improve
communications between the command post (base) and teams in the field I
embarked on a mission to find a simple solution to the problem of
There were several requirements that prevented the use of a repeater
(added complexity, weight, setup time), using a higher power base
station (may damage dog collar transmitters and GPSr
receivers:sup:`1 <#footnote>`__ and only amplifies one side of the
communication), or a portable tower (see repeater above).
The solution was happened upon almost by accident and the improvements
were immediately noticeable. Digging through the back of my car I came
up with a VHF j-pole and fiberglass expandable pole to put it up in the
air. A few adapters later and we were on the air!
The performance improvement was immediate! Suddenly communications were
possible at a much further distance and, when connected to the Garmin
Astro 320, dog collars could be received from a much further distance
Anyone who has examined the efficiency of a "rubber duck" antenna will
know that these stock antennas aren't great and that almost anything is
better. Stepping up to a j-pole antenna is a significant improvement
and then putting that antenna up in the air has a lot of wow-factor to a
[caption id="attachment_1057" align="aligncenter" width="640"] Two VHF antennas, straps,
and mast ready for activation.[/caption]
With the tests complete I built two j-pole antennas: one centered on
155.160MHz, our primary operational frequency, and one centered on the
average of all the MURS frequencies. The latter is used as a
receive-only antenna for the dog collars and hangs below the VHF "ops"
antenna. Both of these antennas are hung onto a fiberglass expandable
pole that holds the antennas up in the air around 20 feet or so. This
pole can be attached to a fence post, command trailer, tent pole, or
laid into a tree branch to keep it upright.
The most expensive part of the project was the LMR-240
feedline:sup:`2 <#footnote>`__ that we used. The antennas were made
out of 300-ohm ladderline with shrink wrap at each end to help keep the
elements out. The pole is actually made for pulling cable and wires and
is made by
It's really strong but isn't crush resistant so you have to be careful
not to step on it when it's laying on the ground.
For about the price of a good commercial antenna we were able to get a
working antenna system that is completely portable/pack-able and
lightweight and takes only a few minutes to setup and take down. It
also doesn't take up much space for storage meaning it fits into the
existing infrastructure without having to make changes.
We've deployed this antenna system several times this spring and summer
and have noted improvements over a variety of terrain. This project
would have cost around $350 for parts if not for donations of parts and
pieces along the way.