Building the popular end fed half wave antenna (EFHW) that performs well can be a challenge, so here’s a few tips on how to make your EFHW work well… it’s often not what you might think.
First, you have to decide what the primary purpose of your antenna is to be? One size does not fit all. Will it be NVIS for regional communications, local net checkins, or will it be used for longer range continent wide contacts and DX?
NVIS
NVIS: This is the propagation mode that’s primarily used on the 80, 60 and sometimes the 40 meter bands. At these low frequencies, the antennas are quite long, so they often need to be installed in a sloping or horizontal fashion. The antenna can be configured as an inverted vee, or even in an L shape if space is limited. For optimum NVIS performance, the highest point of the antenna should be no higher than 35′ (8 or 9 meters) above ground. The idea is, you want your signal to radiate upwards at a high angle. With NVIS your range of reliable 80m low band communications will usually be around 250-350 miles;, ideal for the BCPSN and local rag-chew contacts. With NVIS, the orientation of the antenna is unimportant.
DX
DX is a bit different. For DX, you want to get your horizontally mounted EFHW up as high as possible. As the antenna is raised up, it’s radiation pattern tends to flatten out with more of the RF being radiated towards to the horizontal plane and less in the vertical. My low band EFHW is up between 60′ and 70′, strung between two 2 story buildings.
I worked Catalonia Spain (EA7), an honest 5X9 on 40m on only 100 watts. Two days earlier, a pedestrian mobile on 20m, 5X8, at one point he was peaking over 9, all the while walking around a Riverside California park, and running only 10 watts from one of those small inexpensive SDR transcievers. The antenna orientation of a horizontally mounted antenna is important as radiation is mostly off the sides and less from the ends.
Wishing a low to the horizon omnidirectional pattern, particularly on 20m, I decided to install a second 1/2 wave EFHW as a vertical. So I purchased a 12m, (40′) Spiderbeam mast for CA $215 from Vibroplex. As Vibroplex don’t deliver to Mexico I had it muled down from Santa Fe NM. Made in Germany, these 12m Spiderbeam poles are of excellent quality, are light weight (about 7 lbs), and all you have to do is tape the antenna to the mast as you slide it up.
The results were startling. First contact C5O in Gambia Africa, I beat the pileup with 100 watts.. next VK7AB long path, he said his beam was pointed towards Africa.. We had a 1/2 hour chat.
Getting the omni directional radiation pattern of your vertical down to 5 degrees above the horizon is the secret to DX success. You do this by adding four 1/4 wave counterpoise wires just below the raised matching transformer. No tuner is needed, and the 20m EFHW works fine on 10m being the second harmonic of 20.
Ferrite Cores and Impedence Matching
The smallest ferrite core in the photos is the Fair Rite 2661102002. It’s a special cable core; small, light, this core is made of 61 ferrite material, which has now been proven to be the most efficient option for 40m and up. The larger, heavier 2643251002 ferrite core of 43 material comes in a close second.
https://www.digikey.ca/en/products/detail/fair-rite-products-corp/2661102002/8594114
The above YouTube video is pretty funny; you’ll have to take this guy’s off-beat sense of humour with a grain of salt…but he does his homework.
Mine is wound autotransformer style… 14/2 with a 120pf TDK compensating capacitor. The 61 core works 60m and up.. However due to it’s lower (125) mu, the 61 core does NOT work efficiently on 80; but on 60m and up it works fine giving 90%+ efficiency. and the match is excellent giving 1:1 vswr The antenna wire itself can be just about anything, even speaker wire would work OK… I use #16 stranded house wire.
About the ferrite cores in the first photo below. I’ve tried em all. The original go-to ‘doughnut style’ FT 240 43 has largely fallen out of favour due to it’s lower efficiency; on some bands. If you want an all band antenna 80 through 10 meters the second cable core with the fat form-factor and blue 100pf TDK capacitor (Fair Rite 2643251002 from Digi Key) is the one to buy @ about $8 each. This core can support power levels of upwards of 300 watts SSB or 100 watts FT8 without saturating out and overheating. Key down @ 100 watts I have seen no sign of VSWR creep, a sure sign of the core heating up as it saturates, so it’s quite efficient.
The third core, the smallest, is a bit of an experiment. It’s made of 61 ferrite material, Fair Rite 2661102002. Although it has a smaller cross section and form factor, this core has a proven efficiency of over 95%, approaching 97% on 40m, but only if wound auto-transformer style 14/2 and using a 120pf compensating capacitor. The 61 material core only has enough mu (125) to be efficient on 60m-10m. This is the core I use for my 20m vertical EFHW as noted in the second picture.
In the excellent video above, the use of tape at the feedpoint is really not necessary, the ferrite core is a magnetic device, not a conductive one… for 80M and above the 2643251002 is the best all around with a loss of less than .5db. at 80m… for 40 and up the 2661102002 core, is the one I use on my vertical and both are available from Digi Key.
https://www.digikey.ca/en/products/detail/fair-rite-products-corp/2661102002/8594114
https://www.digikey.ca/en/products/detail/fair-rite-products-corp/2643251002/8594030
As a bonus my 20m vertical works well on 10m being the second harmonic of 20m and becoming full wave. A 1/2 wave vertical on 20 has a gain of about 2.5db over a 1/4 wave vertical. By installing 1/4 wave radials (really a counterpoise) the angle of the antenna’s radiation pattern will drop towards that ideal DX magic 5 degrees to the horizon. VSWR is zero reflected across the entire 20 meter band. Coax is 30′ of RG58u, so the loss in the coax is only .25db @ 20m. Like the 264325002 core made of 43 material, this small 61 ferrite core when wound auto transformer style exhibits excellent efficiency and shows no VSWR creep @ 100 watts key down.
If you want a slightly higher angle of radiation for continent wide communications; for example; on Field Day or perhaps on a POTA trip, just leave the extra radials off and raise the feed point up about 1m above ground. The coax shield will still serve nicely as the couterpoise. As a portable antenna, the EFHW vertical on a Spiderbeam mast can be deployed in about 10 minuites. Without the radial style counterpoise and only using the coax shield as a counterpoise, the antenna does remain efficient. The radials are not essential for antenna efficiency, rather they primarily serve to lower the radiation pattern towards the horizon for a better DX radiation pattern.
If you bring the coax away at right angles or behind the radiator (not parallel) you should not need any decoupling or chokes. and as an option you could provide an ‘earth ground’ at the rig to bleed off any electrostatic build up which can cause RX noisel. An earth ground does not change the characteristics of the antenna itself.
So…..for maybe $50 worth of bits and parts… add CA $214 for a Spiderbeam mast (if you need one), and you can build yourself an inexpensive performng antenna that can be used for both field portable or in a permanently fixed situation.
If you have any questions feel free to send a note to: chemainus@gmail.com
Richard VA7AA/XE1, Jalisco Mexico
