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Linked EFHW Design

Well, I finally did something with all of these well thought out opinions, good advice, and experiences. Now it is time for me to report back on what I ended up doing with it.

As mentioned in my initial query, I use a QRPGuys EFHW matching unit that has a tuning capacitor. Whenever working with a simple single band EFHW, I adjust the matching unit’s tuning capacitor for maximum power out on my FT-817, thus letting the FT-817’s SWR foldback circuit tell me when I have achieved the best antenna match. Experimenting with using that particular matching unit without any counterpoise connected has shown that I cannot achieve the full 5w output from the FT-817 without having a counterpoise. That seemed to be true on every band. So, in my case, as long as I’m using this QRPGuys EFHW matching unit, I will use a counterpoise. Later on. I may try a different matching unit to see if there is another one which can provide full output from the FT-817 without using a counterpoise.

Rather than pursue my original plan of making a Three Band Linked EFHW, the discussion here led me to making a Three Band Trapped EFHW instead. I used SOTABeams Lightweight Antenna Wire and SOTABeams Pico Trap Kits and built my Trapped EFHW for 20-30-40 meters. I started out using the antenna wire lengths that matched what I had previously used for single band versions. I made a three-wire bundled counterpoise using the same SOTABeams Lightweight Antenna Wire, using the counterpoise lengths that were recommended by QRPGuys for 20-30-40m.

I tuned the antenna for each band with an antenna analyzer, by first adjusting the matching unit’s tuning capacitor for maximum power out on my FT-817, and then switching over to the antenna analyzer. Surprisingly, I only had to shorten the 20m segment by a few inches and then add that same length back into the 30m segment to end up where I wanted to be in each of the three bands. I did not make any length adjustments to the three-wire bundled counterpoise. Throughout this tuning period, I looked at the reports that I was getting on the Reverse Beacon Network from sending out a ‘test de k3jzd’ a number of times on each of the bands - I wanted to rely on more than the just antenna analyzer readings.

By using the SOTABeams Lightweight Antenna Wire and one of their medium size winders, I ended up with a compact and light spool to pack, even with the three-wire bundled counterpoise. While my Chasing over the last week showed me that the bands were pretty weak with a lot of QSB, I decided to try a CW Activation anyway. Yesterday (15JAN17) we had a break in the wet weather in WPA, so I went out and used this antenna during my W3/SV-008 activation. I used it as a sloper, with the high end connected to my 25’ pole and the low end with the matching unit 12 inches off of the ground. I laid the counterpoise on the ground, under the sloped antenna. I pointed the high end of the antenna toward the West. Considering the poor band conditions, I think that it did pretty well. There were a lot of simultaneous activations going on yesterday, and there might have been some contest activity, making it a tad more difficult. Nonetheless, a lot of my regular 20m Chasers who are out in the Midwest and on the West Coast who were not out there themselves managed to hear me and work me. I gained a lot of new Chasers while using 30m, with some pretty good range and reports there. I did not make a lot of 40m contacts, which was unusual for me as I have a lot of frequent 40m Chasers. However, I was moving around a little on 40m due to QRM, and RBNHole was not reporting spots at all yesterday. After finding an open frequency on 40m, in the time that it took me to do a self spot with my cell phone, the frequency became occupied. I guess there was some weekend contest activity, because the RBN showed that I was getting out quite well on 40m while I was repeatedly calling ‘CW SOTA’.

To summarize: I built a Three Band Trapped EFHW using SOTABeams components. Tuning was not real difficult due to the QRPGuys EFHW matching unit which has a tuning capacitor. This particular matching unit needed a counterpoise to give me a full 5w output from my FT-817, so I built a three band bundled wire counterpoise to use. During the initial usage during my W3/SV-008 Activation, my results on 20m and 30m were better than I had expected to see - the loss in the traps was not obvious as it heard well and got out pretty well. My less than stellar results on 40m may have been due to issues other than my antenna. It was nice not having to get up and deal with antenna links whenever switching bands. But, yesterday, with the temperature hovering in the 20-25 degrees F range all day, I found that I was getting up anyway to walk around a little to warm up before starting to use the new band.

Jody - K3JZD

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Jody, can you give us the weight of the three system components.

QRP Labs EFHW tuner
Trapped radiator assembly
Bundled counterpoise

Richard // N2GBR

Nice report Jody, thanks for the follow-up. Great topic and discussion.

Total weight of the five components: QRPGuys EFHW tuner, trapped radiator assembly, bundled counterpoise., the plastic SOATBeams winder, and a 36" length or RG-174 BNC-BNC coax to connect the EFHW tuner to the FT-817 is 9.55 ounces.

Would be a bit hard to weigh without including the plastic SOATBeams winder, and you would not want to leave the short length of RG-174 (1.06 Oz) at home so I included it in the total.

Jody - K3JZD

I have done tests using counter poises of different lengths and have found absolutely no difference in tuning or radiation effectiveness with any counter poise versus no counter poise WHEN the wire is an Endfed Halfwave. Forget about it.

The link… I have tried using links, but have had equal succes using very small SPST switches instead. Easier to use in the field.

Better, the no-link, link… I have built mini-traps using T50-2 cores and 500V mica capacitors in parallel. Only one trap is needed for each additional band since feeding on the end. I put the toroid on one side and the cap on the other of the smallest possible piece of perfboard. The trap should be tuned to a resonance somewhat below the frequency of intended use.

The tuner… I originally used the KI6J tuner from an AA5TB design which was later copied by Hendricks. I have found that the losses associated with the varicon capacitor to be identical to the losses using a fixed 81:1 balun. By combining the 81:1 balun with the trapped wire, band-changing is instant.

72, Fred KT5X (aka WS0TA)

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Compares to my 20 + 40M 26ga link dipole with Sotabeam 1:1 balun on a Sotabeams wiinder with ~25ft of RG174/BNC and 10ft of mason line at each end which weighs in a 9oz.