The KJ6VW Half-Square Antenna
By Andy K3UK
I thought I would share this antenna design with folks, it may be
useful for those wishing for a bit more gain and an easy to
make/erect antenna. I had used a half-square antenna before and
had some good results from
one at a previous QTH. I decided to make one for 40M. After hours
of trying ways to erect a 40M antenna I gave up , 33 foot vertical
sections in a small lot get very frustrating indeed.
I had shared my half-square idea with George KJ6VW and he modeled
the antenna and suggested a few changes. Finding The 40M
difficult to handle on my own, I asked George to model the same antenna
concept for 20M. The results were an antenna easy to build, easy
to erect by myself , and performs well. Here's what George
and his software came up with:
"Andy, your half-square
antenna, trimmed for 20m and fed with 75 ohm cable,
would be 20.0 feet high and 32.5 feet long. I assumed #12 wire for the
top and 1" tubing for the verticals. With the verticals ending 10
inches above the ground, the SWR is:.."
For my small lot, an antenna with 3.8 dBi in two desired directions
seemed worth a try. Especially since I already had 75 Ohm RG6
laying around from satellite TV instalations. . I also
constantly retrieve old antennas that
people are throwing away, so I have plenty of aluminum tubing for the
vertical sections. Since George mentioned that the vertical
sections are the ones that would need trimming , I did not feel like
trimming aluminum tubing . So I decided to make the last few feet
at the bottom end of the verticals out of #12 wire. I also
need to have the antenna 10 inches off the ground, I decided to achieve
this by having PVC pipe touching the ground. So, the
antenna looks a tad "ugly" in that I use scrap metals that do not taper
perfectly . I had two very light 15 foot booms from old
Yagis. So I simply used them for the first few feet,and made up
the rest with some narrower tubing and #12 wire at the bottom .
So the diameter of the sections was not to the original one inch
assumptions that George made. More like 1.5 inches for about 15
feet , a couple of feet at one inch and a few feet at #12 wire size!
(picture coming soon) . I fed the antenna at an
upper corner . You may want to consult the ARRL Antenna Handbook
for more about the varying methods of feeding this antenna . You
may also find the document at http://rudys.typepad.com/ant/files/antenna_halfsquare_array.pdf
to be useful.
The horizon section was also made 32.5 feet of #12 wire. That
cost me approximately $18.00. I used F Female -UHF
Male Coaxial Adapters by Philmore (NO. FC71) to connect the RG6
to my SO-239 antenna jack . That was $2.46 from a local store.
My thoughts regarding RG6 were simple, I wanted to see how this antenna
would perform generally , before I invested in 100 foot of more
So , on a hot and VERY humid day, I decided to try erect the
antenna. After a nightmare trying the 40M design and getting
things stuck in everything in my backyard, small 20 foot vertical
sections were easy to handle. . I had the thing up in 10
minutes, no one needed to help me. I used a fence , a tree, and
some rope, to secure the vertical masts. Essentially the antenna
follows a fence line NNE to SSW. I anticipated a few
minutes of trimming to get an good SWR.
After all , my vertical sections were not at all precise to the
original specifications. Low and behold ! The SWR was quite
good first try! Pretty much as George and his software had
predicted. Under 1:5:1 over the entire 20M band ! A miracle
So, what about the results? The first few minutes were spent
comparing it to my other 20M antenna, a home brewed 20M 1/4 wave Ground
plane , mounted 17ft above ground. Here are the
first few RECEPTION results...
G station (England) 559
sp80pzk (Poland) S3
California stations S5
N2NC New Jersey
PA3EBB (Netherlands )
I was very happy to find it a better performer to Europe. It is a
little disconcerting to find the antenna you have been using was
not even hearing Europeans that another simple antenna can get
S3. Tests later in the week have also found some occasions
where stations to my south are copyable on the ground plane vertical ,
but not the half-square. Although the half-square is much better
than the ground plane, the opposite lobe indicated in the modeling
software does not appear to have occurred. Signals to the west or
SW appears no different on each antenna. I have not had a chance
to work any stations further out than 2000 miles to the west or
SW. Perhaps when the band is open, West or South West
signals around 3000-400 miles will be similar to the results I am
experiencing with European signals . My half-square does have
some tree branches around it, perhaps that is altering the gain
directions. I will work next on clearing the branches.
This antenna is movable. I could move one of the vertical
sections in an arc. This would give me the ability to alter the
direction of the radiated signal. Not something I am likely to do
very often, but if I needed a couple of dB more in a certain direction,
to get that "new one" , I could do it quite easily with the
George became more interested in the half-square antenna after
modeling this for me. He experimented with several ideas.
His latest is TWO half-squares and some radials (not usually
associated with a half-square). George has dubbed this a "
half-square beam " and it has a predicted gain of 9.6 dB
Email me if you need more info
about this variant of the KJ6VW Half-Square.
My actual tramsissions with the 20M half-square have not been many, too
busy to get on the air much . But I did work 5-6 Europeans in
a row during the Worked All Europe CW contest. I will post
more on my transmit results during the next few days.