Your opinion and comments on the Half Square antenna

Discussion in 'General Technical Questions and Answers' started by G0GQK, Feb 26, 2009.

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  1. K3STX

    K3STX Ham Member QRZ Page

    It is kind of strange it is not better than the single vertical. However, depending on how high off the ground your vertical was, that could be QUITE an antenna! I had a 40 M vertical elevated about 20 feet with 8 elevated radials and it was a GREAT DX antenna. Your half square should hear best BROADSIDE to the horizontal wire, not end fire! You should have about 4 dB of gain relative to a single vertical. You are feeding it at the top corner, right?

    paul
     
  2. AE5RC

    AE5RC Ham Member QRZ Page

    Half Square Antenna....

    I own and have used a half square . I only have a 10 meter version so anything I say is based solely on the performance on that band.

    I had a vertical for 10 meters (read a cut down cb antenna) at about 40 feet at the base of the antenna. I wanted to see if the half square would work better/same/worse in a comparison. I climbed on top of my house and tied a piece of string to the end feedpoint connector of the half square and reached as high as I could to tie the string to my antenna mast (used some electrical tape to wrap the string so it did not slip down). I tied another piece of string to the opposite end connector and connected that to a small weight and tossed it over a limb in the tree in my backyard. As best I could figure the half square was about 20 feet(the horizontal wire) off the ground. With the coax connected and run into an antenna switch, I went inside to compare the two antennas.

    I made a call and a California station came back to me (I am in Texas). We chatted several minutes and I asked if he could do the comparison. No problem, so I changed to the half square. The California station went away (vertical) and I am now talking to a ZL station. He told me he was using a yagi and had tried to break in my qso several times. I never heard him. Now the California station did, so when the half square was used the ZL came from no reception to readable (I do not remember exactly what signal strength was). That is about the best comparison I can give.

    You can read all about how much this or that any antenna does. I can tell you a half square does work and under certain conditions will grab some dx when other antennas are not producing the goods. Go to Antennas and More web site and take a look at the article about the antenna. It is easy to install and it will work. Now for any other bands aside from 10 meters I cannot say because (again) I only have the 10 meter version of this antenna.

    Good luck.

    73
     
  3. W8JI

    W8JI Ham Member QRZ Page

    Mel,

    Let's look at the facts.

    First, radiation angle doesn't mean a thing by itself. It is the absolute field intensity at a given angle that matters, not the peak angle alone. Any antenna sold as having a low take-off angle is being sold much like a used car vendor would do.

    A dipole at modest height (in wavelengths) has as much low angle field intensity as a vertical does, unless you happen to live where the path goes right to a salt marsh or the ocean in the desired direction.

    The Fresnel region ground affects the half-square just as much as in any other vertical. The earth for several waves out from the antenna forms the pattern, and if it is less than perfect for that distance the accumulated loss and phase shift attenuates the low angle signals. That just a fact we have to live with, unless we can put the vertical several wavelengths in the air.

    So what is a half-square? It is two 1/4 wave verticals with maximum current at the tops spaced 1/2 wave apart that are fed through a half wave single wire feeder. In a perfect lossless antenna the two verticals would have equal currents and the single wire feeder would have some, but minimal, radiation because it acts like a two current sections 1/2 wave and less apart that are out of phase. That's the PERFECT model of the antenna.

    The gain of two 1/2 wave spaced verticals over a single identical element is easily calculated. If you look at broadside gain at this page:

    http://www.w8ji.com/stacking_broadside_collinear.htm

    Gain is 3.6 dB for 1/2 wave spacing for a theoretically perfect lossless system. That's over a single identical element. In a perfect system the addition of that 1/2 wave phasing line will cost about 1/2 dB from radiation in generally useless directions, so you have about 3.1 db gain over a single element in a lossless system.

    Over perfect lossless soil the antenna has about 9dBi gain, while a dipole at 5/8th wave height would have 8.6 dBi gain.

    Now real earth losses added:

    When we throw in real earth losses we have 3.1 dBi gain at 21 degrees TO angle with the half-square. That is the absolute gain peak. It has 1.3 dBi gain at 10 degrees wave angle.

    A dipole at the SAME height as the half-square top wire has 2.63 dBi gain at 21 degrees TO angle, and significantly more gain at higher angles. It has -2.1 dBi gain at 10 degrees, so the low dipole is 3.4 dB down from the half square at 10 degrees wave angle.

    A dipole at 5/8th wave has just over 8 dBi gain at 23 degrees TO angle, that is the absolute peak gain. It has 4.22 dBi gain at 10 degrees, 3 dB MORE than a half square at 10 degrees.

    This is for a perfect feed on all antennas, something easy to do with a dipole but very hard to do with a half-square..... so it is much more likely the half-square would under-perform the perfect feed models.

    Objectively a half square, unless you live in a saltwater marsh, will be about the same as a half wave high dipole at best at low wave angles. The 1/2 wave high dipole will be better at higher angles, while equal at low wave angles.

    This is why the user feedback we get will be mixed. Certainly it will work, but depending on losses or imperfections it will only equal a modest height dipole in the best directions and angles.

    Like many antennas our view of how it works will depend on how poorly or well we install the reference antenna, and how poorly or well we install the half square. It is in fact about equal to a modest height dipole at very low wave angles, so it is more about what we do wrong with one or the other if we see some dramatic change.

    At my QTH a half square was about equal to a ~ half wave high dipole at the best, but for many signal reports was actually a good bit weaker. That's why I settled on either directly phased verticals or high dipoles on the low bands.

    It's very tough to beat a good dipole for a simple wire antenna.

    73 Tom
     
  4. M3KXZ

    M3KXZ Ham Member QRZ Page

    "Objectively a half square, unless you live in a saltwater marsh, will be about the same as a half wave high dipole at best at low wave angles. The 1/2 wave high dipole will be better at higher angles, while equal at low wave angles."

    Difference being, of course, that a half square for 20m has the top wire only 5m or so above the ground, whereas the dipole at "1/2 wave high" is 10m above the ground. The fair comparison is between half square at 5m and dipole at 5m when comparing performance in available space - so half square wins assuming it's highest gain at lowest angles that is wanted, yes? Important on 20m for DX. But then on the lower frequencies then higher angle radiation may be the requirement for NVIS type comms, in which case the low dipole might be the better choice.

    Also....something worth doing....feed halfsquare half way along the horizontal section and you have two verticals fed 180 degrees out of phase regardless of frequency (just make it so the vertical sections are a decent length on each band you want, and the horizontal section gives decent separation like 1/4 to 1/2 wave on all bands). Makes a nice bi-directional endfire array, much like half of a W8JK array when "properly" fed

    Pete.
     
    Last edited: Mar 1, 2009
  5. G0GQK

    G0GQK Ham Member QRZ Page

    Hello everybody,

    Thanks for all the replies, quite a lot to absorb. To AE5RC, I don't suppose really there should be much of a difference between 10 and 30 metres on the face of it, other than when 10 was wide open there was some good ionisation of F3 (?) which would have been worth a few thousand miles. Its good to know that when things do improve, a half square will astonish us

    Hello Tom. I'm still looking for that pot of gold that's around somewhere !
    Big problem though, the highest I can get a wire is 25 feet, and the 30 metre half square legs stop about a foot above the ground. Perhaps if I were able to get it higher it could be better. Had to smile at a comment made on one group about ten years ago. The chap wrote his half square legs were about 10 feet off the ground and would it help if he laid rabbit wire, we call it wire mesh, on the ground below the dangling vertical wire. The reply was "if I were you I'd build a shed underneath it with a tin roof " That made me chuckle !

    Pete, that seems an interesting idea, big problem is, once again, I would be unable to feed it and get coax into the shack. I don't know why I just don't give up ! I suppose we're all the same thinking a new untried antenna might be better than the one we have.

    If we had a few sunspots and some decent conditions all we would need to do is to go down the hardware shop, buy a ball of string, put it under the tap and hang it between two poles. Voila !

    Kind regards, Mel G0GQK
     
  6. AI4IJ

    AI4IJ Ham Member QRZ Page

    It depends on the band...

    A half-square antenna is an excellent alternative to a dipole, for DX, when top height is the limitation. But, if you can get a horizontal antenna at least 1/2 wavelength above the ground, there are better alternatives than the half-square.

    What this means is that few people implement a half-square at the higher HF frequencies - there are better antennas easily implemented at 1/2 wave and higher above the ground.

    I've used a half-square on 20M and it was a decent performer with the top wire at about 20 feet above the ground - better than a 20M dipole at the same height. Not only did it have a better signal at the desired angles of radiation, it also had less noise, as the sensitivity to high angle signals was GREATLY diminished on the half-square, while the dipole was very sensitive at the higher angles. This means that a half-square is a better DX antenna at heights below 1/2 wave above the ground - not so much for the additional gain, but for the ease in pulling out weak DX signals (If you can't hear them, you can't work them).

    73
    Richard
    AI4IJ
     
  7. G0GQK

    G0GQK Ham Member QRZ Page

    Reading all the various comments and articles about the half square I think I'm inclined to agree with you Richard, its the old height above ground thing again. My 30 metre half square, as I wrote doesn't seem to me to be an improvement on the vertical with four quarter wave radials, because its at the maximum height that I can achieve.

    However I bet that if I made a 10 metre half square at 25 feet it would show the characteristics which I read about, low angle take off and the ability to hear distant signals better than those within a thousand mile range.

    Well its always worth a try, and one of its assets is that made of wire it vanishes into the background, it can hardly be seen, but, its only a single band antenna.

    Kind regards, mel G0GQK
     
  8. AI4IJ

    AI4IJ Ham Member QRZ Page

    For 10M at 25 feet, I would prefer an Extended Double Zepp, rather than a Half-Square. It's just a simple 44ft center-fed doublet; but, at 25 feet above the ground, it would probably outperform the 10m Half-Square. You can either feed it with balanced feedline for operation with a tuner between 40M and 10M, or you can use a matching section of ladderline to coax for monoband operation without a tuner.

    A Half-Square is primarily a low band antenna. It really starts to shine at 40m and below. At 20m and up it's an average performer.

    73
    Richard
    AI4IJ
     
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