Gain Antenna For Weather Radio
- Warning: I'm having problems with my 'a' key in case come go missing!
Anyway, I put that antenna up I created last night and it works quite
well! I thought I'd post some of the details in case there are others
in a fringe area that could use just a little more signal. Total cost
was about $50, including 50 feet of RG-6 cable. I had to beef up the
construction due to the wind here in the lower right corner of
Wyoming, but quite a bit of cost can be eliminated by using smaller
PVC pipe without the extra reenforcement or using scrap cable you may
already have laying around.
The diagram can be found here:
For the elements I used four 1/8" by 36" brass rods from the hardware
store. Two of them are used for the center "driven" element, which is
built in two halves, one soldered to the cable's center conductor and
one soldered to the cable's shield. One word of warning: some cable
manufacturers are using aluminum braid for the shield to cut costs.
You can't solder to aluminum, so you may have to crimp a short piece
of copper wire to the shield and then solder the other end of the wire
to the element.
The boom is made out of 1" PVC pipe with a 1" oak dowel run through
the center for high wind strength. The boom is cut to a total length
of 32 inches. A three foot non-metallic mast is connected to the boom
made from more PVC and another oak dowel. Screws at the PVC T-fitting
that joins the boom to the mast keeps the dowels from rotating or
migrating inside the pipe.
The reflector element at the rear is left at its 36" length thanks to
a happy coincidence of math. It is mounted 15 1/2 inches back from
the center of the mast. The director element is trimmed to 33 3/4
inches and mounted 15 1/2 inches forward of the center. The elements
are epoxied in place.
As mentioned earlier, the driven element is actually two pieces cut
long enough for a total length of 34 1/2 inches. Each of the two
pieces should be half this length, with enough extra added for each
pieceto fit through the boom. 18 3/4 inches should work with most
boom materials, but feel free to cut them longer than this at first --
they can always be trimmed more later. Two holes are drilled in the
boom side-by-side, a quarter inch apart, 1 3/4 inches back from the
center of the boom. The driven element should be closer to the
reflector than the director. The diagram has a detail of this.
Not knowing what polarity the antenna should be, I made this version
of the antenna vertically polarized. Because I didn't glue the pipe
sections at the center T-fitting, I can rotate them to horizontal
polarity by removing two screws. At this time I don't know what
polarity the Weather Radio transmitters are, but hopefully tomorrow
the NWS will respond to the email I send them. If horizontal or
circular, I can rotate the antenna to horizontal and eliminate the
non-metallic portion of the mast to simplify things.
Looking at the photo below, you'll see how I coiled up the first
several feet of cable to decouple it from the driven element. The
cable then intentionally leaves the coil such that the cable leaves
the plane the elements are in. This prevents disruption of the
Once again I'll be able to simplify things by running the cable off at
a 90 degree angle if I can rotate the antenna horizontally. Another
suggestion would be to mount the antenn from the rear, which would
make it easy to run the cable out the back and down the mast.
Once completed, the whole thing is clamped to a steel mast.
Oh, and my space bar is malfunctiong now too which is really starting
to piss me off. Once I finalize the design (When I hear back from
NWS), I'll take some better photos and create a downloadable PDF file
with working computer...
Richard H. Brant