Build your own tiny antenna for 80, 40, 20 meters.
EH Antennas are a controversial antenna patent # 6,486,846   designed by Ted Heart www.eh-antenna.com.    Ted claims a scientific breakthrough but I find his explanation of how they work, difficult to swallow.  I have read quite a bit about the EH antenna and in my humble opinion, the claims about the E and H fields don't make any sense.  This leaves us with two possibilities: 1 - the antenna is nothing new or 2 - nobody has properly explained how the EH antenna works.  You will have to decide for yourself.  This much I am sure of;  the EH antenna is physically very small, easy to construct definitely does work.    Many of the critiques of the EH antenna have been based on computer models of wire antennas.   Wire antennas are a 2 dimensional thing while the EH antenna is a 3 dimensional thing.  Trying to apply a 2 dimensional model to a 3 dimensional object doesn't make any sense.   

DANGER There are high voltages present on this antenna and you could get yourself killed if you are not careful!  Also, at one point, I nearly burned my house down.  It seems that somewhere along the line, I drilled a hole in the plastic and forgot I had done it.  Later on, I mounted the capacitor plates so that the hole was between them.  While testing, I noticed the SWR was jumping around so I went upstairs to see what was going on and SMOKE was coming off the antenna!  

How I think EH antennas work
My crude experiments indicate that the EH antenna is nothing more than a matching network connected to a dipole made of short, fat elements.  The only requirement for these short, fat dipoles is that they have sufficient surface area for the frequency they are to be used on (see splatter screen antenna below for equation).   Antenna efficiency is the ratio of the energy that is radiated divided by the energy that goes into the antenna.  The EH antenna does not get hot and has a 1:1 swr at some frequency so it must have a high radiation effeciency.  

A short dipole has a very high impediance.   The matching network must transform the high impedance of the dipole down to 50 ohms to match the transmission line to your radio.  I think that if the surface area of the dipoles is too small for a given frequency, the impedance of the dipole will be too high and the losses in your matching network are too high, making the antenna inefficient.  My experiments indicate that the surface area of the dipoles is the important factor, not their shape.  I played around with various shaped dipoles and they all seem to work about the same as long as they have roughly the same surface area.

There is lots of internet talk about the E and H fields of the EH antenna (thus the name EH), interacting in some special way.  This talk of E and H fields interacting in some special way is all nonsense in my opinion.   Maxwell's laws still work the way Maxwell said they work.  It doesn't matter how the fields are created.   

These little antennas seem to act as a point source of radiation and as such, are bound to have a low gain compared to a dipole or any other antenna which has a radiation pattern that is distorted.  The whole idea of antenna gain is to design an antenna with a distorted radiation pattern and then point the antenna in the direction you wish to communicate.   If the radiation pattern is more distorted than that of a dipole, it works better than a dipole and is thus said to have gain of a certain number of db.  An antenna acting as a point source will have a negative gain because it doesn't work as well as a dipole.

The bottom line is this: my wife will not allow me to build a decent sized antenna so these little antennas are just the thing for me.  They get me on the air and she doesn't have to look at them.  Anyone who wants to see them can come with me into little room over my garage and we can sit with a can of beer and argue about what makes them work so well.  This much is for sure; these antennas do work and have an SWR of 1:1 at some frequency.   The matching network doesn't even get warm so the the vast majority of energy from my 120 watt transmitter must be going off in the form of electromagnetic radiation.  This means that they are indeed efficient radiators!  I have tried every possible orientation for the antenna and the performance is unchanged, which means that they act as a point source (isotropic).

I read recently a comment on EH antennas by TOM W8JI that "operational descriptions almost always include strong indicators of problems with feedline common-mode current".  I haven't had this problem.   As far as I am concerned, the only reason there are problems with RF burns from feedline coax and other similar problems is that the matching circuit has not been properly adjusted for the frequency you are operating on.  My experience is that if you adjust the matching circuit properly, you will get a 1:1 SWR with no nasty RF burns or anything like that from touching the chassis of your transmitter.   Adjusting the matching circuit is quite touchy and may require lots of trial and error.  If you have a problem, contact me and maybe I can help.  

         
80, 40, 20 m, EH antennas living in my garage roof space  -   40 m Splatter Screen Antenna      -    80 m Wastebasket antenna (details at bottom of page)

  dimensions of the brown wire I used on all the coils.

EH antenna for 40 Meter Band
My dipole cylinders and capacitors are made from stainless steel stove pipe, cut with an electric jigsaw all mounted in PVC plastic drainpipe.  The EH antenna is a vertically polarized dipole.  The 40m unit stands about 1.2 meters high.  I get a 1:1 SWR over about 30 khz. and less than 1.2 over 100 khz.  I can get to within 2:1 over the entire 40m band.   My 40m design is from the website of VK5BR http://www.qsl.net/vk5br/EHAntenna20_40.htm   I have made a few changes such as the use of stainless steel for the cylinders.   It has been suggested that the use of ferrous metals may result in losses.   The best thing about stainless steel is that it doesn't rust.

40 meter band EH antenna components ready for assembly 100 mm diameter stainless steel stove pipe  (2 cylinders like the ones to the right, are missing from the photo)

40 m antenna dimensions

wiring diagram of 40m EH antenna

EH antenna schematic

According to Lloyd Butler (VK5BR), the dipoles look like 2,368 ohms with a parallel capacitance of 10 pf.  The purpose of the capacitors and inductors is to match the dipoles'  2,368 ohms and 10 pf into the transmission line's 50 ohms and 0 pf.  I don't know what the two single turn coils are for but I assume they are to compensate for the 10 pf.  Other designs don't have the single turn coils but I thought they looked nice and technical so I left them in! 

The 40 m antenna components are:
1.5 m pvc drain pipe 103mm ID
1 m stainless steel chimney flue 100 mm OD
6 x stainless steel bolts m4 with nuts and washers (flat head counter sink type bolts)
8 m wire 1sq mm (1.2mm dia) solid copper wire covered 3 mmOD

40 m antenna (note CW key in foreground to show size)

CONSTRUCTION
Cut the cylinders to length.  Grind the rough edges off the metal cylinders.  Rough edges can lead to "hot spots" that can cause the PVC  to breakdown causing an arc.  Nothing is critical except the final tuning.  The two coils are held in place with tape or a bit of glue.  I don't know if the direction of the coil windings is critical but I suggest that you stick to the diagram above just in case because I know this configuration works.  The capacitors are formed by having a cylinder inside the PVC pipe and another sliding cylinder with a slit up the side, on the outside held together with cable tie.  M4 stainless steel bolts and nuts were used to hold the cylinders in position and to attach the wires.

Tuning: The final position settings for the adjustable capacitors are very close to the resonant frequency for the LC circuits.  If you have a grid dip meter you can use it to determine if you have the correct number of turns on the coils to allow the capacitors to be set at or near the resonant frequency.  If you don't have a grid dip meter, you can use a noise bridge to set the capacitor positions.  Just use trial and error to find the correct settings for the desired frequency.  If you don't have a noise bridge, you can build one: http://dj4br.home.t-link.de/rauschbr.htm .  If you don't have a noise bridge, you can tune your antenna using an SWR meter and trial and error with your transmitter.  You may, of course, fry your transmitter in the process.

If you don't get an SWR of 1:1 then you haven't got it tuned correctly.   The final position of the sliding capacitor plate is extremely critical with 1mm movement amounting to a change in frequency of 100 khz on the 40 meter band.    Finally I placed the antenna in the roof space of my garage and connected coax and made final adjustments of the capacitors  

updated May 07
If you can't get 1:1 SWR no matter how you adjust the capacitors, you may have to add a turn or remove a turn from one of the coils (ain't life a bitch).   If you can't get a 1:1 SWR, try tuning the antenna at a frequency above or below the band.  If you get it working above the band, that means you have to add a turn to one or both of the coils.  If you get it working below the band, then you will have to remove a turn.   Don't go adding or removing turns until you have done lots of trial and error.  Move one capacitor a small amount and then try all settings of the second capacitor.  Then move the first capacitor a little and again try all possible settings of the second capacitor.  This takes time but is all part of the fun of getting your EH antenna to work properly.  Just keep fooling around and eventually you will get your beautiful 1:1 SWR with no measurable reflected power at all.

Test results:  The 40 m antenna works really well.   I regularly get excellent signal reports over the entire length of New Zealand using my 100 watt rig.   Very impressive for such a small antenna.    For receiving, both the noise level and the signal level are lower than you would expect from a dipole.  Like almost everyone else who has played with EH antennas, I have not made any careful measurements against standard antennas so I have no way to measure antenna performance.  I do have quite a bit of experience with amateur radio and in my opinion this antenna works very well.

80 Meter Version of the EH Antenna:

components for 80 meter version, ready for assembly, 200 mm diameter stainless steel stove pipe

80 m antenna dimensions

The 80m version is exactly the 40 m version with all the dimensions multiplied by 2 so I used 200 mm dia. stove pipe.   My 80 meter antenna is a bit different from others found on the Internet.  My 40 meter unit worked so well that I decided to simply multiply the dimensions by 2 for the 80 meter unit.  I had to reduce the coil windings by 1 turn to make the matching network work.


completed 80m antenna

The top stainless steel cylinder (dipole) is sticking out of the top of the plastic pipe because I could not afford a longer piece of plastic pipe.  The plastic pipe is split down the side because I could not get one with a large enough diameter to go over the 200mm OD stainless steel pipe. 

Data on the internet suggests that if the height above ground is less than 1/4 wavelength, performance will be degraded.  Both my 40 m and 80 m versions are about 4 meters above the ground which is 10 % of 40 m and 5% on 80 m.  

Tuning: Tuning the 80 meter version of the EH antenna is the same as the tuning for the 40 meter version.  The only difference is that because you are operating at a lower frequency, the percentage of the band over which you get a decent SWR is about half that of the 40 meter antenna.  Position of the sliding capacitor plates is extremely critical and if you are not careful, you might decide that the antenna does not work at all.  You have to be very careful and make very slight changes in capacitor position (1 millimeter makes a big difference) until you get things right.

Test results: At first, I thought the antenna was not working but I eventually discovered that the tuning is very critical.  I also discovered that the fluorescent lights in my radio room cause a great deal of QRN.

20 Meter Version of EH Antenna
As with my, 80 meter antenna described above, I decided to simply scale my successful 40 meter antenna down by a factor of 2. 

 
20 m dimensions


20 m antenna components ready for assembly (I eventually replaced the gray PVC with red PVC )

20m antenna

I used aluminum tube because I couldn't find 2 inch OD stainless steel tube to fit inside my 2 inch ID PVC drain pipe.


rebuilt 20 m antenna (exactly the same as the first attempt but with red PVC electrical conduit)

Test results:: The first attempt at the 20 m antenna didn't work because the PVC pipe used was heating up when transmitting.  This heating caused the SWR to be unstable.  I rebuilt the antenna using red PVC pipe of the type used by electricians as conduit.  My first CQ got me a reply form Kamchatka which is just about as far away from New Zealand as you can get.   This doesn't prove anything except that the antenna does work.  I tried to find out the difference in composition between the red PVC by Marley which works well,  and the white PVC by Iplex which doesn't work.  I never was able to find out much of anything of interest.  (note that the Iplex pipe is designed for plumbing, not antennas so don't blame Iplex). Although the 80 m and 40 m antennas don't seem to interfere with each other, they do seem to interfere with the 20 m antenna. 

More tests with noise bridge:   A noise bridge is a gadget so simple that you can build one yourself as I did..  Here is a link to look at if you want to build one  http://dj4br.home.t-link.de/rauschbr.htm    A noise bridge uses a white noise source in place of an oscillator and your receiver as a detector.  It measures the impedance of any unknown, at the frequency that your receiver is tuned to.  If an antenna is working according to theory, the reactance should be 0 (X=0) and the R should be 50 ohms.  In practice, if the antenna is operating correctly, you will get a definite dip at 50 ohms with a definite dip at X=0.

I got the 80 m antenna working by putting 5 turns on the top coil and 6 turns on the bottom coil.  I had cut a bit off the bottom capacitor slider which is probably why I had to put 6 turns on the bottom.  In any case, it gets 1:1 SWR over a fairly narrow range of frequencies and within 2:1 SWR over about a 100 khz range.  Adjustment of the sliding capacitors is very critical.   1mm of movement makes a big difference.  Once you have things adjusted, the bottom slider sets the frequency.  More capacitance lowers the operating frequency. 

Splatter Screen Antenna (SS antenna) (This is all my own design)
For the uninitiated, a splatter screen is something you put over the frying pan to keep the grease from splattering when you are cooking your bacon.  I tried to find a formula for determining the dimensions of the EH antenna dipoles but there doesn't seem to be one.    I decided to experiment with different shapes for the dipoles to see if other shapes will work.   After exhaustive research (about 15 minutes in the local Warehouse, discount store) I found a pair of "splatter screens".   I selected a pair of top class, 11 inch diameter, chrome plated steel, splatter screens for $NZ 2 each.  You should understand that I have very little idea of what I am trying to do here.  I just want a small antenna that is easy to build and works well.  

Splatter Screen antenna.

The matching network is the same as that used in the original EH antenna that I got from the web site of VK5BR     http://www.qsl.net/vk5br/EHAntenna20_40.htm     I left off the two single turn coils as I couldn't figure out what why they were there.  I read somewhere that the short dipole is equivalent to a resistor in series with a capacitor (red box in equivalent circuit below).  If it is adjusted properly, the matching network together with the dipole, looks like a 50 ohm resistor at one frequency.  

   
Schematic diagram of splatter screen antenna                                     equivalent circuit

I suspect that there isn't any reason to have one, series LC circuit upside down from the other but this was adapted from the original VK5BR design so I haven't got around to trying to change it to see if it matters.   I used the same mechanical construction as I used for my original 40 m EH antenna described above. 

matching network for splatter screen antenna 

Splatter Screen antenna wiring

Test results:  The dammed thing works!  What do you know?   It works better than the original 40 m EH antenna.

                
                    initial position                                      vertical                                                 shortened                                     side by side

Making the screens vertical as shown above is not a good idea.  The vertical antenna works fine but is unstable.  Just the slightest touch, and the SWR jumps all over the place.  I suppose this is because the screens are not mechanically rigid so they flop around a bit which changes the capacitance between them.  Anyway I changed the orientation back to the horizontal splatter positioning and did more testing.  The splatter screen antenna has 2 to 3 db more receiving gain than the original EH antenna made with cylindrical dipoles.  It may be that the SS antenna is just physically longer and thus performs better or it may be that the disk shape is superior to the cylinder.  It also may be experimental error!  I tried reducing the distance between the screens and the matching network. The shortened antenna seemed to work about the same as the initial position antenna but I had no accurate way of measuring performance.  Finally I tried side by side but that didn't seem to work as well as the initial position.
                                                                                     
Now here is an interesting discovery.  This discovery may be worth millions but it is my gift to the world.  The diameter of the splatter screen really does matter.   I decided to check to see if the idea of using a circular disk really amounts to anything at all, so I removed the splatter screens and replaced them with two different options.    I tried first a pair of straight, heavy gauge wires of the same length as the splatter screen and its handle.  Then I tried a a pair of 14 inch diameter splatter screens.  The straight wires of about 14 inches, did not work at all.  It was as if nothing at all were connected to the matching network.  My noise bridge gives a reading of zero ohms at resonance, just as you would expect from a pair of series LC resonent circuits.  The larger splatter screen did sort of work except that I ran out of adjustment on the capacitor to the right (see splatter screen antenna wiring above).   I couldn't reduce the capacitance enough to quite give me a 1:1 SWR.  I didn't have a small splatter screen to find out how much below 11 inches I could go and still have success.

The circular splatter screens really do work and their diameter is given by D=KW.  D is diameter in meters, K is around .00697 and W is the wavelength in meters.  For 80 meters this gives a diameter of 558 mm or 22 inches.  For 20 meters it would be 5.5 inches.   I can't wait to try it out on 80 m.  If anyone beats me to it, please let me know.  I suspect that a solid metal disk would do the same job as the fine, wire mesh of the splatter screen but it would be interesting to find out for sure.

Wastebasket Antenna for 80m
I suspect that the surface area of the dipole elements is the critical factor, not the shape.   In an attempt to prove that this is the case, I constructed a matching section modeled after the splatter screen antenna described above.   I designed the matching section for 80 meters.  The capacitors are twice the length of the capacitors for the 40m splatter screen antenna.  The left coil below is 10 turns and the right coil is 9 turns.  The matching unit is just under 1 meter long.  A center "T" mount was glued onto the center because I wanted to check to see if the antenna was directional when mounted for horizontal polarization.   I tried a pair of cheep foil roasting pans for dipoles which did work but they were so floppy, that it was not stable.  When  mounted on a 5 meter tall plastic pipe, there seemed to be no change in signal strength when rotated.   All these short antennas seem to be acting like a point source which is an isotropic antenna (I think).  If the antenna is acting like a point source, that will explain why the performance is not fantastic.

Next I tried a pair of wire mesh wastebaskets for the dipoles.  They are a bit floppy so I will have to add something for rigidity.

waste basket antenna wiring

 
Wastebasket Antenna for 80 meters

The wastebaskets are each 300 mm long with diameters of about 280 mm and 210.  Sitting on the floor of the shack, the antenna got good signal reports from around New Zealand.   The good news is the Wastebasket Antenna has a wider bandwidth (250 khz) than the EH antenna.  The bad news is that it does not seem transmit as well as the EH antenna.   Contacts report my signal is down from the EH antenna which is unfortunate because I really like the look of it.  For recieving, the Wastebasket antenna is about 1 db down compared to the EH antenna, close to the resonent frequency.   The Wastebasket Antenna outperforms the EH antenna as you move away from the resonent frequency.  I don't know what is happening here.  I need to experiment with adusting the matching circuit to make certain that the differences in antenna performance are not simply a result of different matching circuit settings between the EH antenna and the Wastebasket antenna.  I have only transmitted, close to the resonent frequency so I don't yet have comparisons further away from the resonent frequency. 

It is interesting to note that the Waste Basket antenna performed exactly the same when sitting on the floor of the shack with 1 meter of feed coax as it did when mounted about 3 meters above ground in the roof space of my garage with 9 meters of feed line.  I have not yet given up on the Wastebasket antenna.