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 dimensions too 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:
20mhs
"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:.."
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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 costly RG11.

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 to me! 

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...


                                  Half Square                    Ground Plane

G station (England)       559  ...                          NO copy

CT2IZE (Portugal)       S5                                    S3

sp80pzk (Poland)        S3 ,                              NO copy

9K2UU (Kuwait)           S3                              ZERO copy

California   stations      S5                              S5  no difference.

Florida stations ,          S3                                S5

WWV 15Mhz             S9                            S9+10

N2NC New Jersey      S1                             S1

PA3EBB (Netherlands ) S2                      ,No copy.


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  armstrong method.  

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 !!!!!! 

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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.