I use one single, tapped T68-2 core instead of two to obtain the required inductances for 40 and 30 m.
Instead of two SPST slide switches, I use a single SPDT 3-pole on-off-on switch, as proposed by Heinz, @HB9BCB.
I added a common mode choke in order to reduce the effect of unavoidable asymmetries between the radiator and the counterpoise.
Instead of four 10 ft. ground radials, my design can also be used with
a) one elevated, resonant radial, tuned for each band by winding up the remaining wire, or
b) three elevated, resonant radials attached to each other.
The enclosure is also a winder, same as with Packtenna antennas.
I have not yet tuned this one, because it is just too cold outside right now
Enjoy!
73 de Martin, DK3IT
Edit: The details of the tapped loading coil are as follows: With 0.5mm magnet wire, wind 25…26 turns, then add a short tap, then another 20…21 turns. Leave at least 10 cm on either end so that you can adjust the tap by adding a turn on one side and removing one on the other. Now tune the loading coil with a component tester or other device for measuring inductances. The total coil should have 11.5 - 12 uH, the 25…26 turns should have 3.4 - 3.6 uH. It is important to shorten the rest of the coil (i.e. the 20…21 turns) while measuring the inductance of the lower 25…26 turns. The 0.5 mm wire fits on the T68-2 core and should be thick enough for high efficiency and QRP levels.
I did the QRP-Guys (or rather the USPS) an injustice - the antenna kit has just arrived here today 5 days after they sent it. Now I have to wait for the wire I ordered for it’s driven element and four radials to come and the new on-off-on switches.
as for the counterpoise, I am now considering (and hope to be able to compare) several alternatives:
a) four non-resonant ground radials, as in the original design - not so much influenced by differences in the ground, but less efficient).
b) single counterpoise on a winder with markings for each band; fine-tuning for compensating differences in ground, same as @G8ADD has proposed.
c) three pre-tuned resonant counterpoises, soldered to a single 2mm plug with no winders on the end.
d) same as c), but with a small inductor for loading a shortened counterpoise for 40m. Will make the set of cps easier to manage on a small summit. Unclear impact on performance, likely more difficult to tune (narrower bandwidth).
e) single radial with markings and a variable L-network/transmatch for the counterpoise, i.e. adjusting the resonance of the cp by a variable inductor or capacitor. The advantage is that you will need no fully-fledged ATU and do not have to retract and redeploy the cp for a band-change.
When I first started in SOTA, I made myself some resonant end-fed half waves and for the counterpoise, I experimented with lengths by having the antenna analyser attached. I was surprised to find that counterpoise elements of just an 1/8 wavlength looked good on the analyser. I saw no reason why 1/8 wave should work and I reverted back to longer lengths when actually operating. Then I bought myself a linked dipole and a squid pole and the difference was so great I never went back to the end-feds. Note - the end-feds were just being thrown on the top of hedges or into tree branches, had they been taken vertically up the squid pole, I’m sure they would have worked a lot better.
I see your point, but I think it is unfair to compare an EFHW thrown over a few bushes with a center-fed dipole mounted on a squid-pole. With my 3- and 5-band EFHWs on a 6m mast, I get excellent results - often 17 - 20 dB around Europe, and occasionally NA contacts.
The thing about the counterpoise is IMO that in you case, i.e. on an end-fed antenna, the feedpoint has a very high impedance; thus, an imperfect counterpoise will be just okay (often just the braid of the coax). But with my proposed Up-and-outer design, the feedpoint impedance will be in the 30 - 70 Ohms region, thus the counterpoise will be essential for effective radiation.
AFAICS, a linked dipole and an end-fed differ just by the position of the feedpoint (and that traps or links will be symmetrical in a dipole and just one per band on an end-fed).
That’s why I said, I think they would have worked a lot better on a pole.
My point was the counterpoise length of 1/8 Wavelength appearing to be good by the Antenna Analyser - might be worth trying if you have the time to see if you find the same.
Hi Ed,
actually, I can already tell you that it is very different on this vertical / up-and-outer, because I tested in with the previous versions, like this one
Electrically, it is equivalent to the new design; the difference is that the loading coil is an air coil in the first version and wound on a toroid in the new design.
When tuning the first version, even 10 cm +/- make a difference. So 1/8 will not work.
What still surprises me, though, is that the resonant length for the counterpoise is typically significantly less than 1/4 lambda.
This is also equivalent to the counterpoise lengths recommended for the ATX-1080 antenna - they indicate a length of
counterpoise_length = 54 / frequency_in_MHz
But I do not understand where this formula comes from.
My understanding, based on the statements by G. Janzen in his publication “Monopol- und Vertikalantennen” is as follows:
Monopole antennas (usually mounted in a vertical manner and therefore simply called Vertical antennas) are, as the name implies, only Half-Antennas. For these monopoles to radiate, a maximum of current must be able to build up at the base - which requires an electrically equivalent counterpart.
This electrical counterpart was/is called Gegengewicht by the German-speaking antenna experts (in English: counterweight or Counterpoise).
This Gegengewicht/counterpoise can then be realized either exclusively through the earth (Marconi antenna) or by metallic plates/roofs or radially arranged wires, the so-called Radials.
So, radial(s) is understood as a possible realization of the electrical counterpoise.
IMHO, with a little generosity, the two terms can be used quite synonymously, isn’t it?
I believe the term “counterpoise” is an attempt to distinguish between tuned radials (normally quarter wave) and one or more much shorter conductors thrown into a design because they make an antenna show a usable impedance when without them, it doesn’t.
One of the articles I found in an archive of articles by LB Cebik W4RNL pondered the introduction of the term “counterpoise”. He eventually concluded that the term had no established meaning in antenna theory and declined to use it. He was a purist but perhaps his puzzlement over the term indicates a lack of theoretical validity.
But now, some years later, I suppose it is taken to mean lots of different things. Like many things in amateur radio, some are well supported by communications theory and some are not.
Indeed, there are actually about as many opinions as there are experts. Too bad that a joint meeting with all these experts could unfortunately not take place, hi.
BTW, I myself am not an expert on monopole antennas, only a few 100 out of over 28’000 SOTA QSOs were made using such antennas.
Yes that was the article I dimly remembred. I did not remember that he was saying that “counterpoise” had that specific meaning, but that is not how it is used today.
His conclusions are what stuck in my head. That the term had been misused and corrupted steadily through the years.
As you say it would be good if the experts could form a joint view of all these matters and put some fallacies and myths to rest. but that is not going to happen…
I have a resonant efhw for 20m it’s a UK commercial one. I put it as vertical as possible on a 10m pole. So it’s slightly sloping in fact. I’ve had a s2s with Australia on it from g/tw003 a year or two ago. It has no dedicated counterpoise wire attached.
So I like it.
The “Upper and Outer” has a venerable pedigree - an internet search and search of the reflector will turn up quite a bit of interesting info
Shortening of the required length of the element run close to the ground is a well known phenomenon, ascribed to the increased capacity to earth experienced by it. It has been suggested that a way to adjust the length of this element is to monitor the current in it, and adjust for equal current in both legs.
This is equivalent to .18 of a wavelength, or 72% of a (physical) quarter wave which is comparable with the shortening quoted in other sources, though I’d have thought this would be a very ball-park figure, subject to the vagaries of a host of variables.
I suspect the formula may have been derived empirically?
As Cebik points out, many antenna configurations can be resolved into an off-centre fed arrangement - it could be that Ed found a serendipitous sweet spot which provided a good match with the radial at that length?
Here’s an anecdote about the QRPguys antenna. I made the kit Saturday night. My family wanted to hike yesterday so I packed the radio, figuring I’d test it out over at a Michigan State park. I definitely like the smaller footprint of the vertical over my normal 60’ of EF wire. I immediately found two problems though: the 40m torroid wasn’t working properly (I am guessing I didn’t get the enamel off the wire) and I didn’t pack a fresh battery for the KX2. I called cq twice and the power dropped to 5w.
I made a couple contacts on 30m, way up into Alberta Canada. When I switched to 20m I got quite a surprise. In the span of 20 min I worked Romania, Italy, and Belgium along with a few more distant Canadian stations. I’ve only been a ham for ~6mo, and before yesterday I’d made only two DX contacts. So this was one heck of an exciting trip to the park for sure. The last time I used code outdoors it saved my bacon on Mount Guyot. This time I talked to the other side of the world on 5W. I feel like the code gods are trying to tell me something.
Of course, it was probably the conditions yesterday, not the antenna per se. I’m going to straighten out the 40m torroid and give it another shot this weekend (hopefully on a couple of summits).
Yesterday there was the ARRL HF DX contest on, so that will have helped get some activity on the bands. Well done with the DX contacts - it’s quite something to work those distances on QRP!
I’ve just received the wire for the driven element and the four radials so it’s time I get busy and build the kit as well!! Mine will be (I hope) a 20m, 40m, 60m version as I don’t operate CW hence 30m outside of IARU Region 3 is of no interest.
