The half square is a simple antenna design thats been around for a longtime:
- Offers good low angle gain with out the need for radials.
- Little more than 1/4 wave high (40ft at 40m).
- Current nodes/maximums are up high, compared to verticals this should have less interaction with near by structures on the ground and reduce noise pickup.
- 80 degree beam-width, can be fed directly with coax at a corner, or voltage fed at the bottom of one leg. I coax fed mine and put a 1M (million) ohm 5W metal film resister across the feed-point to bleed off any static buildup.
- Only down side is the bandwidth is a bit narrow in the model, but in practice it was more forgiving.
More reading by people smarter than me:
- Part 4: The Open-Ended Cousins - Cebik
- Using the Half-Square Antenna For Low-Band DXing - N6LF
- Bob Tails and Half Squares - K3KY
EZNEC Model: 40m Half Square.
Locations of available trees dictate running the antenna near north/south, the broadside will be near east/west. Plotting the bi-directional 80 degree beam-width on an Azimuth map from my location reveals some useful coverage, a good portion of the Pacific, Australia and Alaska, to the east it'll cover pretty much all of the lower 48, Canada, South America and South Africa:
I've had the antenna up for a few days, on JS8Call where I'm most familiar with what I can hear, this antenna has shown it's DX potential on 40m overnight, with more stations spotted across the Pacific than with the OCFD. Down side is performance (as expected) with closer in stations (~1000 miles) are weaker.
The SWR bandwidth is broader than the model, it's quite usable across 40m with it centered around 7.160 MHz.
Noise pickup is negligibly different compared to the OCFD, a stark contrast to the ground mounted 43ft vertical I had up a while back which was very noisy on receive in my city location.
If I had the room for more than one wire antenna I'd keep this one up, however it's a single bander. The OCFD is back up for now..
The half square can be taken a step further for some real gain (~6dBi at 20 degrees) on the low bands by adding a second one as a reflector, VA7ST built one - A cheap 40m DX machine: the twin half square array, a copy of the defunct Cebik link referenced can be found at https://www.antenna2.net/cebik/content/ao/ao11.html.
Phasing them is also a possibility - Phased Arrays - 40m Twin Half Square.
Unfortunately I don't have the room for one of these on 40m.
Models are good starting point, and a way to investigate and better understand antenna systems. These tools can also help guide us to and validate the final result, if a good correlation is observed in the real world then we can have confidence the patterns and other information are accurate.
The models I have created and made available may contain errors, or overlook something someone more experienced can see. I don't claim to be an expert or authority on the subject of antenna modeling or phased arrays. I simply want to further my own knowledge and understanding of antennas which I find fascinating. Comments, suggestions, discussion are welcome - lonney@gmail.com.
This post is one of several on Phased Arrays.