The EFHW is a resonant antenna - used on its fundamental and any higher harmonics. So an EFHW for 80 metres is about 40m long (typically 132 to 134 feet at the usual heights we use in the UK) and is resonant on 3.5, 7, 10.5, 14, 17.5, 21, 24.5 and 28MHz, more or less, and it is therefore a true multi-band antenna. Some bands will be far enough out to need some sort of ATU - either a minor adjustment on a standalone ATU or to be taken care of by the ATU built in to a lot of modern Transceivers. It is possible to tweak it to get good SWR on all the bands without any ATU - but you may have to add a small loading coil 6 feet from the driven end and a physically small capacitor in the middle of the 134 feet. Mine is fine without either - I am happy to pass it through my ATU as I can then see outgoing (and returning) power on the nice big analog meters. Always good to see your signal going out!
These antennas are deceptive - on the one hand they are just half wave dipoles (on their lowest frequency) and radiate like a halfwave dipole - two lobes at right angles to the wire. On the next band up you get an extra pair of lobes but the nulls are not too deep.
We are well used to driving half wave dipoles in their centre - driving current through low impedances, that suits the transceiver and coax that we have, all fairly normal. Driving a "dipole" at its end involves driving very high voltages and very low currents. We are unused to doing this. It needs special care.
Having one antenna covering all band sounds like a magic antenna! and it can be but there are a few things to watch out for. It needs a transformer to convert 50 Ohm coaxial feeder to the very high impedance found at the end of a half wave antenna. It also needs care to sort out RF coming down the outside of the coax on the outer skin of the conductive sheath - this is invisible and often ignored but it has subtle effects sometimes. RF in the shack can sometimes be detected by "strange goings on" - PC loudspeakers bursting into life, RF burns on your lips or fingers or transceivers that stay in transmit and won't go into receive. However RF in the shack, or on your cable's outside is often missed - it can simple increase the noise level on received signals, create nulls or dead spots by affecting the directional pattern of the antenna or cause interference on nearby things - not always noticed either - maybe the download speeds on your neighbours WiFi reduces dramatically or nearby mobile phones drop from 3G to 2G. Current on the outside of the coax shield can also pick up local interference and pass it into your receiver, not just as noise but a birdie that desenses the receiver, perhaps noticed, perhaps not.
So as well as a transformer you must fit a choke preferably two (in the right places) and earth (somewhere). If you don't, your antenna will work. Antennas always work, but performance may be variable, sometimes ok, sometimes disappointing. Do not compromise, do it right!
Having one antenna covering all band sounds like a magic antenna! and it can be but there are a few things to watch out for. It needs a transformer to convert 50 Ohm coaxial feeder to the very high impedance found at the end of a half wave antenna. It also needs care to sort out RF coming down the outside of the coax on the outer skin of the conductive sheath - this is invisible and often ignored but it has subtle effects sometimes. RF in the shack can sometimes be detected by "strange goings on" - PC loudspeakers bursting into life, RF burns on your lips or fingers or transceivers that stay in transmit and won't go into receive. However RF in the shack, or on your cable's outside is often missed - it can simple increase the noise level on received signals, create nulls or dead spots by affecting the directional pattern of the antenna or cause interference on nearby things - not always noticed either - maybe the download speeds on your neighbours WiFi reduces dramatically or nearby mobile phones drop from 3G to 2G. Current on the outside of the coax shield can also pick up local interference and pass it into your receiver, not just as noise but a birdie that desenses the receiver, perhaps noticed, perhaps not.
So as well as a transformer you must fit a choke preferably two (in the right places) and earth (somewhere). If you don't, your antenna will work. Antennas always work, but performance may be variable, sometimes ok, sometimes disappointing. Do not compromise, do it right!
You can't just add a choke right at the antenna because you will choke the performance out of the antenna! - you need RF current in the antenna wire, that is what sends radio waves out into the ether.
You need some form of counterpoise and adding either a counterpoise wire (that takes up space) or adding a choke down the feeder a bit (8 feet or so) allows that bit of the feeder to act as a counterpoise. This is a subtle requirement that some hams don't realise. Tread carefully.
This antenna has had little press coverage in the radio amateur antenna text books but there is a growing body of hams who have experimented extensively and report on the internet their successes and failures. Thus there is a well known way of winding the transformers, there is good anecdotal evidence, backed up by experiment, on how to earth and where to choke the antenna. There are also alternative ways to do things, but I report here, the majority opinion. Safety in numbers!
The transformer should have a turns ration of 7 to 1, this makes it an impedance transformer of 49 to 1 as you need to square the turns ratio. This allows transforming 50 Ohms to 2450 Ohms which is close to what is found at the end of a dipole of ordinary wire and over ordinary earth. Actual impedance might be anywhere from 2000 to 4000 Ohms but a high voltage feed seems to be very forgiving and 49:1 is fine; some have experimented with 8:1 (i.e 64 to 1 impedance) transformation with little difference (except a slight reduction at 10m - it is hard to make a truly wideband transformer).
This antenna has had little press coverage in the radio amateur antenna text books but there is a growing body of hams who have experimented extensively and report on the internet their successes and failures. Thus there is a well known way of winding the transformers, there is good anecdotal evidence, backed up by experiment, on how to earth and where to choke the antenna. There are also alternative ways to do things, but I report here, the majority opinion. Safety in numbers!
The transformer should have a turns ration of 7 to 1, this makes it an impedance transformer of 49 to 1 as you need to square the turns ratio. This allows transforming 50 Ohms to 2450 Ohms which is close to what is found at the end of a dipole of ordinary wire and over ordinary earth. Actual impedance might be anywhere from 2000 to 4000 Ohms but a high voltage feed seems to be very forgiving and 49:1 is fine; some have experimented with 8:1 (i.e 64 to 1 impedance) transformation with little difference (except a slight reduction at 10m - it is hard to make a truly wideband transformer).
It is difficult to cover a large number of bands with a transformer and custom and practice is to add a small capacitor across the primary winding to give better performance at the high frequencies. Modern designs that work well use 1,2 or 3 toroids stacked together and with the wire going around the stack. You can superglue cores together - once, you will not get them apart afterwards!
The transformer should use ferrite cores such as the FT240-43 or FT140-43 or types -52 To get good broadband performance. You could use a powdered Iron core if you only want one band maybe two but for best broadband performance you need to use ferrites. Powdered Iron cores are painted and have a "T" prefix e.g T200-6 is painted yellow. Ferrite toroids have a prefix of "FT" and are unpainted. You will need more than one toroid if using higher power.
The transformer should use ferrite cores such as the FT240-43 or FT140-43 or types -52 To get good broadband performance. You could use a powdered Iron core if you only want one band maybe two but for best broadband performance you need to use ferrites. Powdered Iron cores are painted and have a "T" prefix e.g T200-6 is painted yellow. Ferrite toroids have a prefix of "FT" and are unpainted. You will need more than one toroid if using higher power.
Two versions that are common are two FT240-43 cores superglued together or three FT240-52 cores put together. Using smaller cores can be done but you may be wasting 20% of your power heating the toroid. I use two FT240-43 cores and use less than 100W SSB. This is good from 40m to 10m and "ok" on 80m. The cores are what I have. As well as a Transformer I use two chokes - described in a previous blog post, the first is about 8 feet or 0.05 of a wavelength of my lowest frequency (3.5MHz) down the feeder from the transformer and is 11 turns of RG58 wrapped on a FT240-43 . The second choke is positioned where my coax enters the shack (above my garage). and has 15 turns on a FT240-31. I run a thick copperwire from my ATU and Transceiver to an earth spike just outside the shack. Not Ideal as my shack is above my garage and not close to earth.
Specific details; I used a primary winding of 2 turns and a secondary winding of 14 turns of 1.0mm enamelled copper wire and a 100pF 3kV capacitor across the primary. I bought the 3kV capacitors on Ebay, they are coloured blue. The primary was tightly twisted with the beginning of the secondary and then the turns wound onto the cores, a crossover turn halfway around the core allows having the entry and exit wires on opposite sides of the core. the turns were not wound around 100% of the core but two small gaps kept to reduce unwanted capacitance - the aim is to extend the bandwidth of the transformer to reduce losses at 10m. I forgot to photograph mine before erecting it - it is at the top of a 30 foot mast, and the coax and choke are led away from the mast, the top 8 feet of the mast is made of wood but the bottom 23 feet is aluminium, an old sailboat mast. Avoid having your coax near metal if there will be RF on the outside of the coax.
Figure 1 shows the transformer, annotated with notes from Steve Ellingtons youtube channel
Figure 1: Diagram of the EFHW transformer (From Steve Ellington)
Figure 2: Photograph of Steve Ellingtons Trafo - he used 3 type 52 cores, I used two type 43
This can be tested on the bench by attaching a 2450 non-inductive resistor to the output and seeing what SWR you get from 3.5 to 29.7 MHz. It will not be perfect. Perfect is the enemy of good enough. The resistors must be non inductive and of sufficient power to cope with your SWR measuring device - I used an antenna analyser. An alternative method is to make two transformers and place them back to back with one 50 Ohm port going to the transmitter and the other port going to a 50 Ohm dummy load.
If you stick to the guidelines I wouldn't bother testing it though - It will work. When you get the antenna built run it temporarily on full power RTTY to give a reasonable amount of power and see how hot it gets after 10-15 minutes. (I don't like to run my transmitter on key down at 100% power). It might be very luke warm as it is probably dissipating 5 Watts. Sealed boxes do allow heat to built up and it can be tricky to drill ventilation holes. It will be fine on SSB or CW, cut your power down a bit if using RTTY or FT8.
The antenna wire can be arranged in a variety of ways, You can place the trafo on the ground and run the antenna wire up a non-conducting pole and then horizontally - an Inverted-L. Do not use a metal pole though. Alternatively place the trafo at the top of the mast and run the antenna wire horizontally, I have used this as my shack is not at ground level.
Figure 3: My installation - a photo my trafo and choke and the metal/wood mast.
When considering which layout you should consider that any vertical portions of antenna wire will (a) give you useful low angle radiation but (b) possibly pick up local interference as most of this will be vertically polarised. So try and keep the vertical portion away from your house (and your neighbours!) and metal masts of course.
Also you have several choices on earthing. If the transformer is on the ground (within 1 to 2 feet) then run an earthing spike from the transformer ground onto a 3 foot copper plated steel rod (B&Q) driven into the earth (the Americans use 8 foot rods but I think they are hard to get in the UK). Place your choke(s) just as your coaxial cable enters the shack - assuming your feeder runs along the ground from the transformer to the shack. Having the coax on the ground this increases ground coupling and keeps RF on the outside of your coax reduced.
If the transformer is up in the air then DO NOT PLACE A CHOKE AT THE TRANSFORMER. Measurements of RF current on the actual antenna (and hence your transmitting efficiency) show dramatic drops if you choke at the transformer. You can experiment with a counterpoise of 0.05 Lamda but it I think most people just place their chokes 0.05 lamda down the feeder coax from the transformer - this allows that part of the feeder to act as a sort of counterpoise - allowing the high voltage RF to develop in the transformer. Do not have this part of the feeder close to a metal mast. Conventional counterpoises are usually a quarter wavelength (0.25 Lamda) and these have been measured as less effective, at least in some installations.
Figure 4 shows my SWR plots from 3.5 to 30MHz without tuning and with no extra components added. I just stuck up 134 feet of wire. The grey lines are the amateur bands.
Figure 4: SWR plots taken with a AA-30 Antenna analyser and its PC software.
Note the minimum SWR points are at; 3.74MHz, 6.84MHz, 10.34MHz, 14.15MHz, 17.6MHz, 21.13MHz, 24.7MHz and 28.22MHz and some of these are actually outside the ham bands. I did not bother tuning the antenna as the SWR is still "good enough" in the Ham bands and in any case I always have a ATU in circuit as I like to see its big SWR meters in action when I transmit. The diagrams below show the actual SWR in the various ham bands.
As you can see 17m (18MHz) and 40m(7MHz) are not great, but fine with a little help from an ATU. 60m (5MHz) is still tunable with an ATU but is poor. Still, 5 bands with no ATU and 2 with a little ATU makes this a really useful antenna, I hate beams and prefer subtle, unobtrusive wire antennas.
The harmonic relationships of the 80m to 10m bands is best at the lowest frequency in each band so to a certain extent this antenna tunes easiest for the CW end of the bands. The recommendation is to adjust the length to give best resonance on the 80m CW band and then remeasure across all bands. You may will not get an SWR of 1.0 (unless you have a corroded cable acting as a dummy load!) but should get under 2:1. The earth conductivity and nearby wires and metal may affect your readings and you may not wish to use a lot of ATU (ATUs always have some loss).
If you wish to continue to search for that elusive perfect SWR - or at least a better SWR profile then there are two tricks to achieve this.
Adding a small adjustment coil near the driven end - traditionally 6 turns on a 1" PVC pipe (1.5 micro-henries) placed 78" from the trafo - this will reduce the SWR minimum for higher bands without affecting lower bands.
A second adjustment is to add a series capacitor to the centre of the 134 foot antenna wire. This increases the resonant frequency on 3.5 MHz but does not affect the other bands as much. It is custom and practice to use high voltage (3kV) capacitors here despite this being a low voltage point on the antenna for half of the bands covered (the odd harmonics) In fact there will be high currents at this point on 3.5MHz and just less than 10.5MHz 17.5MHz and 24.5MHz. The resonances on the higher harmonics are always lower than the theoretical multiple due to the increasing relevance of real wire that gets thicker proportional to the wavelength and the end effects that real wire possess.
We rarely can buy capacitors that have clear data on their ability to carry high RF currents but have found in practice that high voltage capacitors can cope with high currents, I suppose they have a high quality (sic) dielectric. I personally think you should add a high value resistor across this capacitor to leak away static. It won't affect antenna operation but during thunderstorms and nearby static it may make your antenna a bit quieter. A 10 MOhm resistor should suffice. I have seen no one else mention this so I guess it is ok without it.
If you can't quite fit 132 feet into your garden there is also a shortened version that uses a coil, this time near the far end of the wire. See Steve's videos for details. You can also make this antenna for 7MHz and get good performance on 14,21 and 28MHz. Both will load up on 6m but the multiple lobes might mean you'll miss some signals and a 6m dipole or vertical is easy to make and takes up little room.
To a certain extent this is not an antenna for beginners, a simple wire dipole does not need much experimentation and will not require much adjustment - provided it is not near bits of metal and has a balun at its centre. (it "works" without it but may be noisier or have subtle RF problems)
The EFHW WILL have RF on its feeder coax, you may need to experiment to get rid of it. Most find the choke at 0.05 of a wavelength is sufficient. If you have lots of metal nearby you may need extra chokes and earth spikes and maybe even counterpoise wire added to the trafo box. Of course the EFHW always "works". Every antenna "works". It is up to you to decide how well it "works". The criteria is not just how many stations you work, the criteria is also how noise gets into your receiver and how much RF you are sending into things nearby. An antenna that allows you to work the world but sets off your neighbours burglar alarm is not a good antenna.
And that is as far as I am going with this antenna. I hope to gather some statistics on its performance using WSPR. The radiation patterns can be seen using MMANA-GA, although endfed antennas are difficult to model - there is an example included in the software. This antenna has multiple lobes that increase as you move up in frequency so it is not perfect. But it is convenient. Less visibly annoying than a beam and you get 40 and 80m.
On the other hand the subtle problems with RF current may prove to outweigh the convenience. One author gives a recommendation that EFHWs are ok as temporary or portable antennas but should be avoided as permanent home shack installations. I will persevere with mine for a while and see how it goes. I am also building a low cost cobweb!
References: (checked May 2023)
Steve Ellingtons youtube videos https://www.youtube.com/@n4lq
good for antenna current measurements with various earth/counterpoise arrangements
MMANA-GAL is downloadable from http://gal-ana.de/basicmm/en/
See also facebook pages: https://www.facebook.com/groups/440907656780779 there used to be a facebook page for Steve Ellington but it has disappeared lately. I don't like facebook!
https://vu2nsb.com/antenna/wire-antennas/multiband-efhw-antenna/ for a negative (but balanced ) review of the EFHW by Basu VU2NSB. Worth reading but don't let it stop you trying one yourself.
73 de Ian McCrum, MI5AFL
