My End-Fed Half Square Antenna

[marsofold]

My first post here so please hold your fire

I put up an end-fed half-square antenna for 20 meters between two north-south trees near my house at 20 feet up. Used AWG#10 wire coated with heavy rubber insulation from an old spool of wire my former company was pitching out. I expected to have a velocity factor of around 0.94 or so, but my Autek RF-1 declared 40M (7.21MHz) resonance at 53 feet, so I guess due to the thick insulation the wire's velocity factor is actually about 0.78. I'm using a 49:1 transformer from eBay (radioman79) that seems to work well. I had tried an LDG transformer, but had no success with it. Due to the second tree's connection point being a few feet lower, I made the first vertical section a foot higher than the second to try to compensate for the height difference by equalizing their peak current points. So the dimensions are 14ft vertical, 26ft horizonally, 13ft vertical (and 6 feet to ground). The 14 foot feed vertical's lowest 18 inches was trimmed and replaced with a short retractible whip antenna. A short alligator clip jumper connects the end of the whip to the 49:1 transformer lug. Thus I can conveniently adjust the total whip length at head height to tune the antenna for perfect resonance on a daily basis if necessary. Used a 7 ft long ground wire (0.05 wavelengths on 40M) to a metal ground rod. And five ferrite beads also spaced 7.5ft out on the 200ft RG-8X coax feeding the antenna. At 40M it is high angle horizonal polarization, on 20M it is a half-square with low angle vertical polarization. At 7.21MHz the SWR meter barely flickers, going to 1.2:1 at the edges of the band. On 20M, it is 1.32:1 at center, and 1.38:1 at the edges. Just checking, 15M at center was 1.4:1. So I'm kinda pleased. I'm in West Virginia and 40M stations out 1200 miles come in strong. On 20M I've heard South Africa. I've been using an old Index Laboratories QRP-Plus, but just bought a Yaesu FT-891. The menus look daunting and I have yet to turn it on. I'm also putzing with a #4AWG spiral radial for 40M.

Anyone else playing around with end-fed half-squares?

 

[secret squirrel]

Awesome work.

 

[1KT001]

A drawing would be ideal to see what you're talking about.

Thank you.

 

[fourstringburn]

Un disegno sarebbe l'ideale per vedere di cosa stai parlando.

Grazie.

Not too many speak Italian around here but I believe you're asking to see a picture or drawing of his antenna

 

[1KT001]

Non molti parlano italiano da queste parti, ma credo che tu stia chiedendo di vedere una foto o un disegno della sua antenna

Yes

 

[fourstringburn]

Yes, I would like to see his antenna too. I haven't heard of a end fed "half square", just an end fed half wave if this is the same thing.

These end fed half wave antennas seem to be the latest fad in antenna design, but it seems without an effective transformer, it wouldn’t work very well and will have great losses in the transformer. This is why a low SWR is achievable.

Because these are usually horizontally hung it seems to be nothing more than a vertical antenna in a horizontal position using a transformer due to a lack of counterpoise being half of a dipole antenna.

A simple dipole antenna would be much better.

 

[BJ radionut]

Build a Half Square DX Antenna - Radio Amateur 05-1997

It's about as simple as they come. And it sure works f William Van TUburg KG8AN 5198 West Valley Circle Portage MJ 49002-1932 Fig. 2, Feeding ihe cable and

www.radioexperimenter.us

Half-Square Antenna: Easy Wire DX Antenna | Amateur Radio Club Oroville CA

w6af.com

A cheap 40M DX machine: the twin half-square array

A cheap 40M DX machine: the twin half-square array Overview -- the basic half-square A simple half-square antenna for 40M is cheap and...

www.yf1ar.com

Wire_Antennas_for_Ham_Radio

 

[marsofold]

I strongly disagree about end feds being inefficient, but will not argue about it. Half square antennas have been around for awhile. I first learned of them from on4un's low-band dxing book. http://on5au.be/content/a10/scv/scv4.html has quite a bit of information about them, including the end-fed versions. My reading on W4RNL'S write up on them is that they are an easy way to get a low solid angle of radiation for the least height, with the vertical wire parts acting as a pair of phased vertical elements. Basicly, you pick a band to get low angle vertical polarization using 1 wavelength of wire. Then you route the wire with the first 25% going up vertically, continuing for 50% of the length horizonally, then going downward vertically for the last 25%. Then the wire is trimmed to resonate at its fundamental frequency that is HALF of the design frequency. So, my design for 20M is trimmed to resonate at 40M. I get a mostly omnidirectional NVIS pattern on 40M, and a low angle bidirectional 74 degree wide pattern on 20M. As W4RNL shows, there is negligible difference whether high impedance end feed or low impedance corner feed is used. End feed gets me multiband use, although with very different patterns on the two main bands (20M & 40M). Although the 49:1 transformers well match a halfwave length wire, they still have very acceptable SWR results on the frequency of which the wire is one wavelength. I am considering making an end-fed transformer with a TAPPED secondary winding to choose multiple high impedance values such as 64:1 and 81:1 for a selectible end-fed SWR match.

 

[1KT001]

Whatever antenna you decide to experiment with, I'm glad you try. We will all have an extra reference if you tell what you discover.

Good luck with your work!

 

[sp5it]

So is it half square or endfed antenna, because those are two different animals.
Mike

 

[Captain Kilowatt]

Yes, I would like to see his antenna too. I haven't heard of a end fed "half square", just an end fed half wave if this is the same thing.

These end fed half wave antennas seem to be the latest fad in antenna design, but it seems without an effective transformer, it wouldn’t work very well and will have great losses in the transformer. This is why a low SWR is achievable.

Because these are usually horizontally hung it seems to be nothing more than a vertical antenna in a horizontal position using a transformer due to a lack of counterpoise being half of a dipole antenna.

A simple dipole antenna would be much better.

An end fed half-wave is definitely NOT simply half of a dipole. If it were, it would be a quarter wave and would be an easy match to 50 ohms. The fact that any end fed half-wave antenna has an extremely high impedance, it requires a matching transformer as the driving impedance is in the order of several thousand ohms. An end fed half-wave is also VERY MUCH more forgiving of a counterpoise. Some even call them ground independent. The low SWR is not due to great losses in the transformer. If the transformer is built properly, it should be a 49:1 ratio btw, it will exhibit decent SWR on the bands on which it was designed to be a half wavelength or a multiple thereof. I made an end fed half-wave a couple of years ago and strung up in an inverted L configuration with a total length of around 135 feet. It actually performs rather well: better than I had expected, in fact.

 

[binrat]

Since the whole lockdown thing started I have made close to 200 EFHW antennas. Gave away most of them. Along with half squares (corner fed), EDZ (pain for portable use) linked dipoles, trapped dipoles, wire yagi's.
An end fed half square would be a full wave in length wire wise.

 

[fourstringburn]

An end fed half-wave is definitely NOT simply half of a dipole. If it were, it would be a quarter wave and would be an easy match to 50 ohms. The fact that any end fed half-wave antenna has an extremely high impedance, it requires a matching transformer as the driving impedance is in the order of several thousand ohms. An end fed half-wave is also VERY MUCH more forgiving of a counterpoise. Some even call them ground independent. The low SWR is not due to great losses in the transformer. If the transformer is built properly, it should be a 49:1 ratio btw, it will exhibit decent SWR on the bands on which it was designed to be a half wavelength or a multiple thereof. I made an end fed half-wave a couple of years ago and strung up in an inverted L configuration with a total length of around 135 feet. It actually performs rather well: better than I had expected, in fact.

End fed antennas are in a sense half of a dipole because there is no return current flowing in a equal path.

Anytime you NEED a transformer, coil, or other matching device this means there will be losses in that device. Judging an antenna by the contacts made isn't a good judgment.

Many people think a transformer balun does indeed work as they intended because their SWR went down when they put one in. This is possible but only over a short span of frequencies in a one band
antenna. More realistically it is more probable that loss has been introduced into the system. Loss anywhere always makes the SWR read lower.

What I said is what I stand behind, "A simple dipole antenna would be much better"



From W8JI:

Can we end-feed a halfwave antenna, or end-feed any antenna, without a ground or counterpoise?

The answer depends on what we want to call a "ground". This simple rule applies to all end-fed antennas, and this rule cannot be broken. The rule is:

Current flowing into the antenna's end must be equaled, at that end point, by the same amount of current flowing into a ground or counterpoise of some type.

An end-fed antenna must have something attached to the feedpoint that carries the same common-mode current away from the feedpoint as current flowing out onto the antenna! The counterpoise can be accidental and not physically obvious, such as the outside of a coaxial cable's shield, parallel currents on a balanced feed line, or currents on a mast or metallic support. This is true no matter how many series traps, isolating devices or systems, or common mode suppression devices, installed at the feedpoint. This current would be called common mode current, and it always causes close-in, and sometimes even distant, radiation.

The counterpoise could also be currents flowing on an intentionally installed radial or counterpoise system, but even an intentional counterpoise results in currents dividing between the intentional counterpoise and accidental paths, like the feed line. Currents divide by how "easy" each path is, or the impedances of the various paths, at the antenna feedpoint. Without a reasonably-sized feedpoint counterpoise, even if we add common-mode chokes at the feedpoint, or use an isolating transformer or network at the feedpoint, voltage across the isolating device increases until the same end-current flows. Even without a direct electrical connection, displacement currents through stray capacitances will cause the same common mode current to flow on the feeder, or perhaps into another unwanted path, at the antenna feedpoint!

What misterminates the matching stub or feeder on an end-fed antenna?

One of the most common arguments we hear is the end of a half-wave antenna has infinite or near infinite impedance, so it does not require a counterpoise or "ground".

The end-impedance of a half wave antenna, even at exact resonance, is never infinite. The end-impedance goes through a relatively broad maximum when an antenna is approximately resonant as a half-wave, but the dissipative and/or radiating part of that impedance is limited to a few thousand ohms maximum, even for very thin conductors primarily having low-loss air insulation. The presence of lossy dielectrics, or use of a thicker conductor, reduces impedance further.

Because impedance is not infinite, finite voltages and currents are required to apply power to, or extract energy from, the antenna. The antenna end-impedance is always some finite value between a few hundred ohms (for very thick antennas, like large diameter tubing or tower sections) to perhaps several thousand ohms for very thin wire antennas that are up high and in the clear. Because the antenna end-impedance is some finite value, sometimes even lower than we might expect, significant current must be forced into the antenna end. The feed line or stub connection cannot force current up or out into an end-fed antenna without equal current flowing into some form of counterpoise at the feed line or stub connection.
Also, without equal load impedances on each conductor, like a symmetrical dipole would have, it becomes impossible to have perfect feeder terminal voltage and current balance. The end-fed antenna is grossly non-symmetrical, or unbalanced. To have a non-radiating feed line, the balanced feed line must have exactly equal and opposite currents and voltages at the feedpoint and all along the line. This means feed line currents in both conductors must flow into some type of similar termination at the antenna feedpoint, otherwise the feed line will radiate. The worse termination imbalance becomes on each feed line or matching stub terminal, the greater unwanted feeder radiation becomes.


Why does a problem exist with end-fed antennas?

Kirchhoff's Law has been around a long time. It is a perfect unbendable rule, just like Ohm's law. It says, in a roundabout way, current leaving one point must be matched by current entering the same point from some other path or paths. In other words, at any junction, we cannot force current out into something without the same net current coming from something else.

This means we cannot force power into a single terminal load. There has to be a return path of some type, even if it is not obvious. The path in a high frequency AC system (like an antenna) does not need to be a direct connection. The path can be through displacement currents (currents through electric fields), but there MUST always be a return path to the source. In the Zepp antenna system, or any end fed half wave, this displacement current must get back to the feed line somehow. If it didn't, it would have no current at the ends.

In a normal "push-pull" center fed fed dipole, displacement currents largely (but not totally) flow from one side to the other. This establishes the electric field, and allows current to flow outwards into the wires hanging "open" in space. With an end-fed, current flowing from the stub or feeder out into the end of the radiator must be returned to the opposing conductor of the feed line. This returned current (called displacement current) always equals the common mode current flowing into the antenna end. Without a suitable counterpoise, common mode or radiating currents must flow onto the feed cable or supporting mast. This means, lacking a proper counterpoise and common mode isolation, an accidental (and generally unwanted) feed line or mast common-mode current must exist. In the Zepp or J-pole (both are electrically identical), or with any form of end-fed halfwave, the mast, balanced feed line, or matching stub has to carry common mode, and to some extent must radiate. If the antenna did not have such common mode, it would be impossible to apply power to the antenna.

 

[marsofold]

So is it half square or endfed antenna, because those are two different animals.
Mike

When I read this, I know that the poster did NOT read the link I provided, since the link proved the exact opposite. Kinda of a bummer getting this on my first post. I'm not going to argue over labels, whether somebody wants to call it a dipole (not me), a half wave, or a half square. Call it whatever floats your boat, I don't care. The half square design originally used a tapped resonant parallel tank circuit for the 50 ohm match, fed at the END. I use a more broadband solution for my match which is working well for me on both bands.

 

[marsofold]

My antenna is grounded at the transformer. Might be a while before I post here again.