EH STAR antenna for 40m

About 3 years ago I was looking for a mono-band 80m antenna and came across a schematic for an EH vertical antenna designed by Ted Hart, W5QJR. It looked interesting so I bought a second hand EH Venus and stuck it at the end of the garden about 4 feet above ground level. I had an A/B antenna switch in the shack and I switched between my Fritzel OCF (off centre fed) 80m – 10m dipole for a few evenings rx just to see how it performed. I was amazed that the EH rx was only 1 S-point down on the dipole which was strung along the garden at a height of about 30 feet at its highest point, down to 10 feet at its lowest. Even more interesting was the fact that the signal to noise was much better on the EH

which meant that the signals I received were much ‘cleaner’, easier to copy and less fatiguing on the ears. I decided to open up the EH antenna to see what it looked like inside and was pleased with its solid construction. I then decided to build one for 40m so I joined an EH yahoo group. I then found that a lot of hams see this type of antenna as a dummy load, works only in conjunction with common mode currents, snake oil etc. etc. It is a very controversial antenna for many hams to say the least. That said, its mode of operation appears to be very different to the conventional Hertzian-type antennas, it has a physical length of just under 4m, worked reasonably well just 4 feet off the ground, and for ops with limited space or needing a visually-low antenna, this looked too good to ignore. However, this antenna build I would say is for someone who can follow the instructions precisely or for those with advanced knowledge of RF engineering. I fall into the first category but I learnt an awful lot about antennas and was well happy when I finally managed to get the EH to actually work (on my third build). !! I then found a review article in the 2002 edition of the RSGB (Radio Society of Great Britain) RadCom which more or less confirmed what I had found performance-wise in my quick & dirty receive test. I do like to play when it comes to antennas and although I do not fully understand how the EH works, the only way I can try to understand it is to build one. Theory is fine and I understand why the Hertzian antenna paradigm is so strong within amateur radio but amateur radio is also about experimenting and I like to keep an open mind in all things. One caveat here, tuning an EH is entirely different to tuning a Hertz-type antenna. A Hertz antenna relies on antenna resonance and low VSWR being as close together as possible for maximum radiation. The E&H waves for Hertzian antennas are also out of phase and do not combine to produce maximum RF until they are at least 1/3 wavelength from the antenna. The point of maximum radiation for an EH antenna is based on the simultaneous phase relationship of the EH waves at the antenna and a purely resistive 50 ohm load. If you do not follow the EH tune procedure to the letter, it ain’t gonna work. Basic operation: The EH can be thought of as a short fat vertical dipole. It has two aluminium cylinders one stacked above the other. The space between the two cylinders is for a phasing coil. Below the lower cylinder is a tuning coil and below this is what is known as the source coil. The various design parameters for the band of interest can be found using a small program called eh.exe

Please refer to Figure 2: The cylinders act like radiating elements. The EH components of the radiated waves are respectively the Electrical and H is the magnetic waves. The phasing coil is necessary to ensure a 90 degree phase shift of the EH waves at the antenna itself, not its near field. The in-phase EH fields results in an extremely strong RF field produced at the antenna. The amount of phase shift is 6 degrees and maximum radiation can only occur when the EH waves are in phase (at the antenna) and not at the antenna resonance /low VSWR point for Hertzian-type antennas. Figure 2 below is the build schematic for an 80m STAR EH and is shown for illustrative purposes only.

The tuning coil and the number of turns required can be obtained from the eh6.exe program but essentially, this coil is a piece of wire with a length that is resonant for the band of interest. The source coil enables an exact 50 ohm impedance match with hopefully, no reactive components. More on the tune later. Materials and equipment required:

1. Aluminium cylinders. You can be creative and use beer cans, baked bean cans or whatever. I sourced my aluminium cylinders cheaply from a B&Q-type shop that sold these cylinders for air conditioning purposes.

2. Plastic soil waste pipes are ideal for use as formers on which the

aluminium cylinders and coils sit on. The diameter of the former is more or less standardized and you pick the correct diameter for the band of interest. For my 40m EH antennas I used a former diameter of approximately 2.25 inches.

3. Wire gauge is fairly flexible and you can use whatever is in your junkbox

or you can buy 12 or 14 gauge single strand wire from your local DIY shop.

4. My soldering skills although improved of late are still pretty cr$p and in

order to mount the cylinders onto the plastic former and to wire up the coils to the various cylinders I used a pop rivet gun.

5. One of the most useful bits of kit for building EH antennas is the use of a

glue gun. During the tuning stage you need to be able to squeeze the matching coil both ways and measure its tune parameters. A spot of glue works wonders in keeping everything where it should be, whilst you decide what to do next.

Equipment:

6. A field strength meter (FSM). You need one of these because its almost impossible to tune an EH without keeping an eye on maximum signal radiation.

7. An antenna analyzer. Beg or borrow the use of this bit of kit because it will make the tortuous EH tune stage that much easier and quicker to accomplish. I tried tuning an EH using a VSWR meter and FSM but gave up. I quickly bought a second hand MFJ 259B which is a great bit of kit.

8. You will need an SO239 chasis mount in order to connect the coax to the antenna.

9. You will also need to make up a short piece of coax with two flying leads, one will connect to the EH ‘ground’ and the other one will be looking for a decent swr match on the tuning coil.

Build stage: Open up the eh6.exe program and input the band of interest and its chosen frequency (usually mid-band or whatever) with all other variables. Other variables are the diameter of the cylinders, wire gauge and diameters of the phase, tuning and source coils. The screenshot (below) is a hypothetical 40m EH with a cylinder diameter to cylinder length of 9:1. You can change the angle of radiation by altering the cylinder diameter /cylinder length and I used a ratio of 9:1 because I was interested in high angle local hops. I also built a second 40m EH using a cylinder diameter /cylinder length of 3.1 to listen to lower angle stuff.

Screenshot of 40m variables

1. Cut cylinders to length and solder or rivet to the plastic former. Please refer to Figure 2 for cylinder spacing measurements and also where to place the various coils.

2. When connecting the phasing coil wire to the bottom of the top cylinder ensure you place the wire as close to the edge as you can.

3. Ensure the tuning coil wire runs up centrally up the plastic former. I used fairly rigid solid strand wire for all coils which makes the job a little easier.

4. A word on the tuning coil. In order to ensure that the EH tune went smoothly, I took selected bits off the outer insulation off the tuning wire.

See image below. The reason being is that it is easier to find that ‘sweet spot’ of pure 50 ohm resistive during the final tuning stage if you can actually make contact onto the tuning coil.

Tuning coil and fly lead from source coil looking for a low VSWR, maximum radiation

and point of resonance

5. Before I got to stage 4 I measured the length of wire needed for the tuning coil, added a bit more and found out where its resonant frequency was at. Its easier to be lower in frequency i.e. wire length too long than to add bits of wire. I used the MFJ 259B for this (go to advanced mode then ‘resonance’. One strange quirk of my MFJ is that I always found 2 resonance ‘dips’ fairly close to each other i.e. within 2 MHz or so. I trimmed the tuning wire for resonance on the higher frequency reading. The next stage of tuning is critical so I turn to Ted Hart’s EH book to describe and illustrate it.

Figure 3 First tune stage in shack

I normally tune the EH in two stages. The first stage of tuning takes place in my shack which is in the basement. This is situated 3 m below ground level. One of the nice things about the EH (like most antennas in general) is that if it hears well, it will transmit well. During my last EH tune I knew it was going well when I connected it to my IC-736 and heard local and not so local stations chatting away – a good start. When I have found maximum radiation (as measured by my FSM) and that sweet spot of 50 ohms at its point of resonance I tune it again in its permanent spot on the mast. The EH is very sensitive to any extraneous objects close to it and is easily detuned. Luckily, this second tune stage is much easier to do than the first stage. It’s also a good idea to read Ted Hart’s book in its entirety because you also need to ensure you use the correct electrical length of coax cable, make an RF choke etc. etc. I will upload this book onto the CT site as well as the eh6.exe program. What does it perform like? If you have tuned it correctly, you should be pleasantly surprised by the lack of noise and static. If it’s as noisy as your typical Windom or trapped vertical it has’nt been tuned properly. It ain’t no pileup buster but you can hear and get out reasonably well. It’s also perfect for mobile use because you do not have to worry about groundplanes, it’s easy to transport and it also works reasonably well not too high off the ground. Best of all, although time consuming to build and setup, they are very cheap to homebrew and you get to add to the general knowledge base of the ham fraternity. Do I understand the principles of the EH – nope, nor do I care, as long as it works in the way I intended. This aspect of ham radio is interesting for me in the sense that Hertzian antennas reign supreme at the moment but the guy who invented and got the first patent on radio (Tesla) said that the concept of radiating waves (Hertzian-style) is a very inefficient way of doing it. Tesla built his transmitting antennas on the basis of conducting RF energy around the globe using the geo-physical properties of the Earth itself (albeit at ELF/VLF). Tesla knew a thing or two about radio and the electromagnetic properties of mother earth and much of his earlier work has been sequestered but that’s another story.