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Linked EFHW Design

I am using a QRPGuys EFHW Mini-Tuner with my FT-817. This is essentially the same as the Hendricks tuner unit, only without the case. I have had success using this tuner on 40-30-20-17-15 meters while using mono-band half wave Antenna wires and the recommended length of Counterpoise wires. However, storing the wire set for one band and getting out the different wire set for a different band has convinced me that I need to build a multi-band Linked EFHW version. That would be less to carry and would sure make it a lot faster to switch bands.

My design question is : Do I have to make a linked Counterpoise wire as well as a linked Antenna wire? Or, could I get away with just using the 40m length of Counterpoise wire all of the time? Somehow, the right way to do it sounds like make a linked Counterpoise wire. But, I thought I would throw this out and see if others would share with me how they have built their Linked EFHWs, and how well they have worked out for them.

Thanks,
Jody - K3JZD

In such cases I tend to use two or three wires of different lengths and all connected together at the tuner. I think a linked counterpoise is an over elaborate addition.

I agree with Richard (of course - as he’s the expert) - if you make counterpoise wires for each band, have them taped together and always connected. This is what I do with my tripod mounted vertical and it works just as well as having the individual wires attached seprately. It’s much more practical for packing and set-up.

73 Ed.

Hi Jody -
I (and others I have read about) have found that a counterpoise doesn’t seem to make much difference with the EFHW. You might see about simplifying your antenna by trying things without a counterpoise as well as the other suggestions posted here.
ALSO, instead of links for adjusting your antenna length for different bands, you might look at the traps available from SOTABeams or ones you can build yourself. I now have a “no-tune” three band EFHW that is delightfully easy to set up and to operate with. And it works great without a counterpoise.
73, Etienne-K7ATN

Hi Etienne,
You may well find that the outer of the coax ia acting as the counterpoise, if no other is attached. As long as one only runs QRP, this should not create too many problems.

Ed.

Hi Jody,

This is my homebrew variation to the QRP EFHW and tuner (impedance transformer).

73, Andrew VK1AD

That’s nicely put together Andrew. I used to use the same connectors as you have there until I was told about these things.

They don’t tarnish, they fit together and pull apart easier than those car spade connectors and you don’t need to take gloves off to connect/disconnect them.

I have a linked EFHW for 40-60-80 with a HB matching unit. On 5w I find counterpoises make no discernible difference and the short coax feed screen seems to be enough.

Last weekend I experimented with using traps in the counterpoise, here’s what I’m playing with. For a variety of reasons I’ve lately been putting up verticals, so I have a 33’ mast that I raise with 33’ of wire. For 17m and 20m bands I have a 9:1 unun, and the tuner in the kx3 matches it (i also have a link 5’ from the ground on the vertical wire but it turns out I didn’t need it). No counterpoise needed for those bands. For 40m and 80m it’s not an EFHW. I normally lay out one or two 33’m and 66’ counterpoise wires per band (with a switched balun set to 1:1 for 40m and 4:1 for 80m, and a coil for 80m). But I find it a real PIA to deploy and stow these wires. My wife hikes with me, and she really doesn’t like waiting. I bought Sotabeams W3DDZ traps, put 33’ of wire on one side and 22’ on the other. I connected two of these to my vertical in the backyard, and it worked great on 40m. It was the middle of the day, and 80m was too noisy to check. I didn’t have time to test 80m that evening, and now I’m on travel for work. Will try it when I get home. So this configuration reduces the number of counterpoise wires by a facter of two. I’d really like to have four counterpoise wires, so this factor of two is worth it for me.

Cheers,
Kevin

To me the obvious solution is a counterpoise for 40 but shorten it for other bands by coiling up the far end of it around your fingers, marking the positions for other bands with coloured tape.

Brian

1 Like

I have used end fed half waves in the field since 1963, put up on hundreds of occasions, mainly on 80 m and in non-amateur context on 2.8 MHz for the first decades. Properly voltage resonated I found them in no need for counterpoise what so ever, except for the capacitance of my small QRP rigs to the universe! I just pruned the wire length until touching the box had no effect on tuning or loading.

In practice this was somewhat affected by (low) height above ground or moving more than a few percent in frequency. So I soon settled for 39 m on 80 m and just a few, but random, meters of insulated wire on the ground to increase the capacitance to cope with higher return current on either side of resonance. That was all there was needed. In a pinch I would simply put one hand on the box while transmitting.

This became a standard outfit for my rucksack till the present day. Later I added 20 m to the arsenal for DX work. Then it came in handy that same principle applies to every multiple of a half wave. So most often I have used the 39 m wire as a 2 lambda LW for 20 m, taking advantage of its directivity if possible. Since only the far end half wave needs shortening due to end effect, overtone resonances become progressively higher in frequency than the integer multiple of the fundamental. That, along with lower and lower resonant resistance with increased number of half waves, puts some increased demand on the meager counterpoise. So, as much as I have always advised against a stake in the ground for current resonated antennas due to its ohmic resistance, I added clips for 2-3 tent pegs to my ground wire. Even that alone works fine with an antenna resonated to exhibit a few kohms. It also eliminates corona discharge and static bites!

I have never carried a coax on my hikes; I build hi-Z tuners into my rigs. But of course the shield of any coax from an ATU works the same as my ground wire. Sorry for the long text!

73, Villi TF3DX/P

5 Likes

Ditto on these RC power connectors - I took off the croc clips on my SOTABeams linked dipole and replaced them with these about 4 years ago and have have absolutely no problems with them.

Ed.

Andy, thanks for the feedback.

I will give the bullet connectors a go, I have ordered a set of 4mm gold connectors, not from the UK.

Funny you should raise this as a discussion point. Last night on Mt Stromlo I broke one of the 20m links on my homebrew linked dipole which is okay for Op on 20m but not so on 40m. I managed to strip back a short length of insulation and twist the exposed wire around the neck of the opposite spade connector. As it turned out the T Index was through the roof, no NVIS on 40m, not a single VK or ZL chaser on 40m. :frowning:

The link will be repaired (for now using spade connectors) for tomorrow’s S2S extravaganza.

I will retrofit the bullet connectors later.

73 Andrew VK1AD

Just for clarity Andrew - these are not the “12v auto bullet connectors” - they’re too “clunky” - these you can get from the Hobby King Australia warehouse - they are intended for RC cars and boats etc.

Ed.

Getting off topic. Yes thanks Ed, I do know the difference. I have 5.5 mm gold bullet connectors fitted to my LifePO4 batteries for which I made an adapter to 30 A Anderson PowerPoles.

Lets get back to the EFHW discussion before this post is hijacked. :slight_smile:

Cheers, Andrew VK1AD

My thanks go out to all who took the time to offer their thoughts, suggestions, and/or experiences regarding EFHW design and usage.

I have some of the gold RC power connectors all ready to go for making a linked EFHW. But the notion of using a trapped EFHW resonated with me (pun intended). While it looks like it will take a little longer to make and tune, I like idea of not having to stop and lower the antenna to be able to change bands. So, I have ordered some Pico Traps from SOTABeams and I will be making a 20-30-40 meter Trapped EFHW.

Whenever I’m using my End Fed Transmatch (I hate to use the word “Tuner” even though that has become the common terminology), I take advantage of the FT-817’s SWR Foldback circuit. I watch the power output indication on the FT-817 display and rotate the capacitor on the transmatch, centering it on where I see the FT-817 showing maximum power output rather the watching the tuning LED on the transmatch board. So, with a Trapped EFHW, I should be able to change bands in just a few moments.

Since I have lots of the SOTABeams Lightweight Antenna wire available to work with, if this three band Trapped EFHW works out well out on the summits, I will be making a 15-17-20-30-40 meter version later on. And, I may still go ahead and make a linked EFHW for 20-30-40, although with the bands being as changeable and wobbly as they are right now, it will probably be impossible to do any kind of real comparison test with the trapped version. By the time that I switched antennas, the band will probably be behaving differently.

As far as the EFHW counterpoise goes (which was my original question), there were lots of differing opinions on the need for one, as well as how I might do it. I liked the idea of making just one three-wire counterpoise which consists of lengths for 20-30-40 taped together. Easy to deploy, and pack. So, I will start out with trying that approach. And I will also experiment with not using any counterpoise at all, again keeping an eye on the FT-817 power output indicator.

If this thread remains open for a while, I’ll come back and report my results.

73,
Jody - K3JZD

SSSh Andy,

Don’t want everybody using these. Apart from the advantages you mention I find them easier to disengage and engage without inflaming my arthritic joints too much. I use them for connecting to 300 ohm feeder for my doublets as well for dipole links. I got mine for the same place we get our batteries.

73
Ron
VK3AFW

My approach is different. I have been using it for four houndred activations. First, no counterpoise. I have found absolutely no effect on signal at the other end using a counterpoise of any length with a halfwave wire. Second, no links. I have made traps using T50-2 cores and mica capacitors. I can make them very small and light. Antenna wire is #26 teflon coated. And lastly, no tuner. I use an 81:1 balun, and make minor antenna wire length adjustments until it is matched. Band changing is instantaneous, just change bands with the radio, done. a two band trapped wire is easy to do. Three bands takes more work as adjustments of wire lengths may interact a little. I have done four bands, 15/20/30/40 with three traps, but it took quite a bit of patience. - Fred KT5X ( WS0TA )

Similar experience made with more than 3’000 SOTA QSOs (incl. dx to VE, W, JA, VK, VK7, ZL).

Traps made from T-44 cores and mica caps, POLYS-26 wire used for the EFHW radiators, 1:64 impedance couplers wound on FT-82 and FT-50A cores.

Never connected counterpoise wires to EFHW radiators because an EFHW radiator of proper length (not quite as usual with inserted traps, hi) is self resonant and the return path for the very low current at the feedpoint is provided by stray capacitance (see 0.05 wavelength “counterpoise” simulation and conclusion by AA5TB).

Fred, are you using 2 or 3 turns for the primary on your impedance couplers (to cover 7-21 MHz with the same coupler)?

1 Like

I have been using three turns. Have never used two turns so can not compare results of one to another… fred