What do you call an end-fed three quarter wave antenna with a quarter wave counterpoise? Or is it an end-fed full wave antenna with a folded quarter wave section? Or maybe even an end-fed half wave fed with ladder line?
Here are some hints. It doesn’t need any ferrite toroidal cored transformers; so no hysteresis heating effect. It doesn’t need any radials; not 120, not 16, not 4, not even one. It can be erected vertically, horizontally, as an inverted V, an inverted L, a sloper, or even upside down!
An upside down antenna!
In fact the first users of this antenna routinely used it upside down – hanging from the bottom of a gigantic balloon filled with highly inflammable hydrogen gas. The antenna to which I refer is the Zepp and the gigantic hydrogen-filled balloon is, of course, a Zeppelin.
In my previous post I talked about YouTube experts presenting solid cases for the use of a large radial field for ground-mounted vertical antennas. We also discussed how a ferrite toroid core in an End-Fed Half Wave antenna could potentially overheat and cause illegal harmonic radiation. I needed a solution for a vertical antenna that avoided both of these concerns.
A quick look back at the work Steve Yates AA5TB did on End-Fed Half Wave antennas gave me the idea of trying a Zepp, so I built one. A Zepp is basically a quarter-wave length of window line with a half-wave length of wire attached to one conductor of the window line. It is strictly a monoband antenna and it is not quite resonant – but close.
The window line could be replaced with ladder line. In fact I tried both. The wider spacing of the ladder line may have been the reason why I got a better SWR than with window line. In either case a tuner may be needed to get the SWR down to 1:1 (if indeed you feel that is really needed).
A variation of this antenna is the J-Pole. The J-Pole is very similar except that the window line conductors are shorted at the feed end. The window line is then tapped at a point away from the feed end where the impedance is 50 ohms. That seemed like an unnecessary complication to my way of thinking.
I built my Zepp for the 20m band and strung it up rather haphazardly as a low sloper in my backyard just to try it out. It worked without any delicate adjustments. Neither the length of the half-wave radiator, nor the quarter-wave window line matching section seemed critical.
“Life is too short for QRP”
For testing purposes I used my antique, original, non-ND, Yaesu FT-817 paired with an equally long-in-the-tooth LDG Z11 tuner. Remember: “life is too short for QRP” but despite that I managed to get QSOs in Georgia, Mississippi and Kansas from my QTH in southern Ontario with just 5 watts into my low slung Zepp.
So how does it work? Frankly I don’t know so I’ll defer to experts in antenna theory. I watched a video by Stan Gibilisco W1GV (SK) that offered a convincing explanation of the theory. All I need to know is that I have another proven antenna to take to the field for operations out in the Big Blue Sky Shack.
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Ham Radio Outside the Box 
You wrote “It is strictly a monoband antenna”. Not quite true. The antenna portion, being 1/2 wave long on the design frequency, is 3/2 waves long on the third harmonic frequency. And the feedline, being 1/4 wave long on the design frequency, is 3/4 waves long on the third harmonic frequency. So the impedance at the end of the antenna portion is high on the third harmonic, just as it is on the fundamental, and the feedline inverts the impedance on the third harmonic just as it does on the fundamental. This means that if you design for 40 m you can use it on 15 m.
Because of end effects not affecting the “inner ends” 1/3 and 2/3 of the way along the antenna portion on the third harmonic, the antenna portion will be a bit short on 15 m. You can fix this by attaching short stub wires 1/3 and 2/3 of the way along the antenna portion. These provide capacitive loading at the third harmonic and only have a slight effect on the fundamental since they are attached near a voltage minimum, current maximum point (the antenna centre). Go back and forth adjusting total length and stub length until you get it right on both bands.
Of course this will work on other odd harmonics too, but the amateur bands don’t really line up that way except for 40 m and 15 m.
David VE7EZM and AF7BZ
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That’s an interesting idea David and thanks for the input. I’ll build a 40m version and check it out.
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How about 80 meters and 30 meters?
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I don’t use 80m very often and for portable deployments a Zepp will be very long. I sometimes get on 30m, but 20m and 40m are my goto bands out in the field.
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You might think that such an antenna cut for 80 m would work well on 30 m but the numbers aren’t right. If the antenna is 132 ft long it will be resonant at about 3.55 MHz, fine for CW. But because of the end effect problem described above, the third harmonic resonance might be up around 11 MHz and the currents on the two wires of the feedline would be badly out of balance. You could try adding a short drop wire somewhere near 1/3 of the way along the antenna and shortening the antenna a bit. The drop wire would pull the 11 MHz resonance down a lot faster than it would pull the 80 m resonance down but there would be an unwelcome effect on 80 m too since there’s quite a bit of voltage 44 ft from the end of an 80 m half wave antenna on 80 m. You’d have to go back and forth with antenna lenght and drop wire length to get it as good as possible on both bands. This is like the 40 m/15 m problem, only worse since the numbers are more out of line.
Cut for the phone end it would be worse yet. A 120 ft antenna would be about right for 3.9 MHz but its third harmonic resonance would be above 12 MHz.
There’s another problem with any end-fed antenna. On harmonics the impedance at the end drops quite a bit as the order of the harmonic increases. An 80 m antenna might be up around 2500 ohms on the fundamental but by the time you get to 10 m the impedance at the end will be a lot lower than that. This exacerbates feedline balance problems as well as matching problems.
That’s why I like centre-fed doublets, low-loss high impedance feedlines, and tuners. If erected inverted V style they aren’t much harder to use in the field than end-fed wires, though their radiation patterns at higher harmonics can be interesting to behold!
David VE7EZM and AF7BZ
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