A shortened, 20-foot half wave vertical
With toroid loading coils
June 21, 2007
This is an idea I have wanted to try for some time. It is a shortened,
end-fed half wave antenna that I will use on my backpack and marine
mobile outings. Normally I use PVC tubing to make the loading coils.
This time I replaced them with small toroid coils. For each coil
I glued two T50-2 cores together and wound 25 turns of #24 ga.
enamel wire. Actually I started with extra wraps then removed turns
until the antenna centered on 14.250MHz. I would have preferred to use
heavier wire and larger cores, but it was what I had in the junk box.
Here is a closeup of the tiny 1/2" coil against the Cabelas 20-foot
support pole. The ename wire at the bottom is twisted from the extra
wraps being unwound from the core. I may shrinkwrap the coils later to
protect them from the elements. How did it work? See report below the
next photo. . . .
I had only a short time to test the new
antenna this evening. With five watts from my Yaesu FT-817, I made it
from Colorado to Washington D.C. and Dan, NE3Z, who sent me a 5x6
report. This was excellent considering the SFI was 66, the K index was
3, and there was deep fading on the band. Afterward I called CQ and was
picked up by AB3DD/mobile in Maryland. He gave me a 5x4 from his car
compared to his 5x6 mobile signal.
I was in the front yard surrounded by 35-foot trees on either side and the house just fifteen feet away. The tuner was my homebrew parallel match unit seen here
at the bottom of the page. I noticed in tuning that, unlike my larger
PVC core coils, I had to retune as I moved across the band, indicating
a higher Q value in the toroids.
Below the next photo are the dimensions I used to make the antenna. I
hope to try this on 30 and 40 meters and maybe use plug-in coils.
I used #24 ga. stranded wire for the
antenna itself. Why 24 gauge? Because I bought a 5,000-foot
roll at a hamfest for $10. There are three sections of wire.
The center length is 10 feet, 8 and 3/4 inches. The two coils attach at
the ends of this wire. Then, the two outer wires are both 4 feet, 4 and
5/8 inches long. The antenna is fed at one of the ends. The actual
total antenna length is 19.5 feet to fit the fiberglass pole I will use
while operating pedestrian mobile.
----------------///------------------------------------///----------------[M] <match unit
. . . .