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Marry
a 2 meter ground plane with an HT I built the 2m ground plane
like the instructions showed in the project link above.... although I
just used 3 legs instead of 4. Please refer to it for lengths using
the handy calculator provided as a starting point. Stupid
Ham tricks: The previous week I had
attended a radio club meeting where the topic was HT antennas and how well
they performed, which was to say not all that well for the most part.
They usually depended on using your body as a poorly coupled ground
plane or counterpoise. I was bored one evening and thinking about
that while flipping through the hamuniverse web site. I saw the 2
meter ground plane project, and the "nerdtenna" idea started to
come together.
The parts
list:
Whats going to happen here
is that we're going to build a 2 meter 1/4 wave antenna and mount
that on a short section of very stiff coax, and put this (via an adapter
or 2) on a HT.
I soldered first and cut
second. In this case I took what would have been the ground wire
(bare copper), straightened, and inserted it into the center conductor of
the SO-239. Solder that in. I took the other three wires
(red/white/black), stripped the ends and bent hooks into them and put them
into 3 corners of the SO-239. You're going to bend these so that
they are 120 degrees from each other and down about 30-45 degrees. Get
them in the general direction you'll want them when you solder them in.
You can fix it later, so don't sweat the details. Let this cool a
bit since the connector body will be wicked hot for a little while.
Once it cools, check to make sure you have got good solder
flow.
I'm going to wave my hands
here and assume you'll figure out how to terminate both ends of the coax.
Crimp or solder, I'm not religious. Tip to tip, mine ended up
being about 20 inches. I wouldn't go much longer, since it'll bend
under it's own weight and I'd be worried
about over-stressing the HT connector. I actually cheated
and cut a good end off a damaged cable I had sitting around so I only
needed to solder on one connector. Use a meter to make sure you don't have
any shorts.
OK, now lets trim the
antenna "elements". I mounted mine on a MFJ-259
and kept trimming till I was happy. YMMV, (your milage may
vary), offer not valid in Delaware or where prohibited by
law.
These should get you
close, but if you have a good VSWR meter or antenna analyzer, you
could sneak up on these and probably get a better trim. Mine tested under
1.5:1 144-148 MHZ, so I think thats good enough.
It turns out that by
looking straight down you can eyeball these to about 120 degree angle.
A little off doesn't seem to effect things much. The "dip"
from horizontal for the ground plane wires should be about 30-45 degrees.
Again, pretty easy to eyeball and close seems to work pretty well.
You can also balance it on your finger tip (minus the coax) and it
turns out it will lean away from the wire that needs to come up. If
for any reason you think this will be exposed to rain/snow, weather seal
the connections, and put a little non RTV bath and kitchen caulk around
the vertical base.
You have to remember that
these wires will get bent for whatever reason, and you'll be putting them
right, so don't get too obsessed with the angles. Just try and get
them straight, equally spaced, and equally deflected
down.
Now we get to the nerdy
part. Going outside, I keyed up a local repeater using the "rubber
duck" antenna. I got through, but had reports of a fair bit of
noise. I swapped in the "nerdtenna". The reports back were
full quieting and some questioning that I was still on my HT. While
I was outside, the wife let it be known that I looked like the silliest
thing she'd seen for awhile. She thought it looked like an umbrella
frame. Ah, no one understands genius in its own
time.
The nerdtenna ranks pretty
low on the practical scale. You probably wouldn't walk down the street
using it (Hey, you could put someone's eye out!). I did it more as a proof
of concept, yet the more I thought about it the more I liked it.
It's not something you'd leave on, but you could fold and store it
pretty easily. I made mine out of scrap I had lying around (I only
used one new PL239). It would be cheap even with new parts. It
performed unexpectedly well over the stock antenna (which I guess isn't
saying much). I'm thinking it would make a good backup antenna for
when you needed more reach. For a new ham with just a HT, it could mean a
cheap way to hit local repeaters with a solid signal. In a pinch,
you could gin up a taller unit by supporting the coax against
a building or with a pole. Another ham here at work
suggested soldering a fishing swivel to the top so you could haul it into
the air suspended with small cord or string and feed it with rg58 to
the HT.
If any piece breaks off, it's trivial to fix. The gain.... would be equal to about half of a theoretical dipole or minus 3dBd. And thats my "Stupid Ham
Trick"
Jim - W6JMF
Email Jim for questions: Editor's
note: By using this simple method described in the project above,
you can extend the range much greater by the simple addition of more coax
and a ground plane to your ht..  Monitor police, fire, ham radio, rescue, ships and more!  Hamuniverse.com uses Green Geeks Web Hosting! |
