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I tried to build a multiband EFHW antenna as described in articles by PA3HHO, PD7MMA, G0KYA and many others. I decided to start with a short 40/20/(15?)/10 meters version without any loading coils. Surprisingly, no matter what I tried I didn't manage to make the antenna work on more than one band. I was hoping someone could explain where my mistake was.

I used FT240-31 ferrite core for 64:1 (and later - 49:1) transformer, about 18 meters of wire (П274М, Russian equivalent of British D10 - I've used it many times before for long wires, dipoles and delta loops) and 2 meters of RG58 as a feed line and counterpoise at the same time. The second end of the cable was connected to a 1:1 balun. The antenna was installed in inverted-L configuration on a 10 meters long fishing rod.

Here is a photo of a transformer and 100 pF capacitor:

enter image description here

I easily got SWR from 1.5:1 to 1:1 on 40m. However the best I could get on 20m is 4:1:

enter image description here

I tried to get rid of the capacitor, to change it value with a variable capacitor, to change the 64:1 transformer to the 49:1 one, to change the length of the antenna, etc. Currently I spend three weekends on this project. No matter what I tried I get a single band antenna.

It looks like I'm missing something. Maybe the loading coil is not optional in this antenna, maybe it's important to use mix 43 (not 31) as other authors did, maybe something else. What would you do to make the antenna work on 2+ bands?

Aleksander Alekseev - R2AUK
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6 Answers6

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Eventually I managed to make the antenna work on more than one band. I used a modeller (CocoaNEC) to approximately determine the impedance on each band of interest for my antenna configuration (inverted-V on a 10m long fishing rod). The impedance was about 2450 Ohm. Thus I rewinded the transformer to 1:49. Also I used a 1:1 balun (8 turns of RG58 on FT240-31 core) to eliminate any common mode current. Using a variable capacitor I've found a capacitance (138 pF in my case) that gives the best SWR plot:

enter image description here

No counterpoise was needed since it's role was played by the coax in the 1:1 balun. Then I replaced a variable capacitor with a constant NP0 capacitors. You can find a little more details here. The article is in Russian, but Google Translate should manage.

The antenna was tested on all band where it has SWR < 3: from 80m to 15m. QSOs were made on all these band. However, subjectively the overall performance of the antenna is not great comparing to the performance of a regular dipole. I wouldn't recommend trying to repeat it, at least definitelyly not with cores I've used.

Aleksander Alekseev - R2AUK
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See this YouTube video titled: "The 49:1 Half-Wave End-Fed Antenna Transformer, Part 1." https://www.youtube.com/watch?v=MgZap6xWZLs

It says:

49:1 with 3 to 21 windings on the transformer is good for 40m & 80m bands

and

49:1 with 2 to 14 windings on the transformer is good for 40m, 20m & 15m bands.

I made the 2 to 14 with an FT240-43 toroid and 100 pF capacitor. I connected a 66ft vertical wire up a tree with 15 meters of coax and SWR is less than 1.3 on 40m, 20m & 15m bands.

Pyroyd
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I used a 2 to 14 wrap on a T240-31. Close wrap first 7 turns and run cross turn close to the first 7 then close wrap the last turns. You can adjust the spacing and it will lower or raise your SWR. Works for me, only had to adjust it once. Then I hot glued the turns so they wouldn't move. Also check out Steve Ellington videos on his research. This was his idea. Anything is worth a try.

Mike Waters
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Rick Riddle WD4DT
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Please excuse me for perhaps stating the obvious, but you need to cut the antenna wire for a half wave on 40M approx 66 feet, it will work ok on 20 and 10 Metres where there are multiple half waves on a 66 foot wire.

My homebrew EFHW 49:1 matching unit is attached to 132 feet of wire and works very nicely on the normal harmonically related bands 3.5 - 28 MHz and not too badly on the WARC 10.1, 18 and 24 MHz bands. Photo before I added the capacitor.

enter image description here

I used dual FT240-43 cores and 1.6mm enamelled copper wire 14 AWG.

Having been a seagoing radio officer, I learned to over engineer things a bit HI

73 and good luck Tony G3ZRJ

Tony
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I think your original wire was too long, 29.5 feet (overall) and type 43 core/s should have been used for 40, 20, & 10 meters without a tuner and all bands 40 to 10 meters with a tuner and the transformer ratio should be 64:1 for this length. Ron W4BIN

Ron W4BIN Youvan
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This is NOT 64:1 more like 144:1 and core is wrong must be 240-43 go back to the PA3HHO, PD7MMA, webb and read again the short an t with out smal coil wil be 10-20m only fit small coil it will be 19/20/and 40m Pieter

Pieter
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