After two years using a 40-15m EFHW trapped antenna for SOTA activations, this past autumn I started to looking for a more light and flexible antenna solution.
Discussing the options with Ignacio EA2BD he reminded me of this thread, then, after reading the detailed information and interesting comments I decided that George KX0R tuner would be my choice to build.
As chaser and after more than hundred SOTA QSOs with him I can say that his signals are always good in this part of Europe.
Also, lately I like very much to chase in the 60m band and find that (among others) one of the EU activators I have heard always in good shape on that band is Bruno HB9CBR/P, then I asked him about his portable setup. Bruno kindly gave me the details of the station he use over the summits which are are as follow: Elecraft KX2 with internal ATU and the antenna is a 11.2 meter long wire with a 1:4 UnUn and 4 radials, each 4.25 meters long. It was built and designed by Heinz/HB9BCB. The antenna is used as inverted “L” in a 6m flagpole. As Bruno comments, for multiband use the antenna tuner is a must .
I was facinated to know that his small antenna can produce such good signal on 60m!
This definitely convinced me which antenna and tuner combination I had to build.
With 60 to 15 meter operation range in mind and always using my KX2, my goal was to simplify the construction, then, I removed the swr bridge, some switches and aditional capacitors. But, instead I put one rotary switch like Alejandro LU1MAW .
I have not made any changes to the original design because if something goes very well, why to change it!! Below my ugly drawing:
I have used some parts from my “junk box” like rotary switch, 500v silver mica fixed capacitors, toggle switches, etc. I found an appropriate plastic box here:
I have replaced the top cover, with one made with PCB material, to keep room for the rotary switch + toroid core height, it fits on top of the box, this way I get 7mm more in depth.
The toroid core is one T106-6 that I have bought here:
The winding is the same as George ones (3+3 turns primary and 16 turns secondary)
I added one small piece of pcb to the back of the rotary switch and secured the toroid to it by double-sided adhesive tape . The whole set is perfectly secured against the bottom of the plastic box.
Polyvaricon variable capacitors are from here:
They have 6-160pF + 4-60pF sections and comes with 6mm diameter metal shaft extension ideal to fit tuning knob. As George advises for safety I do adjustment at low power, when match is found caps admit the full 10w power from KX2 without any problem.
First time bench test show that it tunes from 20 to 4.300 ohms in the range of 60 to 15M band. Then I went to the field for RBN test with the same wire sizes of Bruno HB9CRQ antenna (11.2m inv “L” + 4x 4.25m radials) , concentrating in 5 to 21 Mhz bands, the most difficult band to find match was 7 Mhz, but reports on RBN were satisfactory in all bands. The next step was to make an activation with this new antenna + tuner setup
For the occasion I went with Ignacio to EA2/NV-032 Artxueta, you can read full report here:
Weather was sunny but with a very strong and gusty wind which tested the strength of the new antenna that resisted perfectly. I worked 60, 30 and 20m with good results, but was a little dissapointed because I could not match in any way the 40m band!! Perhaps I made a mistake selecting T1 tap ?, as the antenna is near quarter wave on this band his Z (according MMANA simulation) could be near 50 ohms, then, should have used 1:1 tap for T1 ? I never did more test to confirm this teory…
Instead I cut a new radiator wire at “random” size of 41feet or 12.5 meter and keeping the 4 x 4.25m radials system I made field test of this new antenna, matching this time very easy from 60 to 10M with good RBN reports as well. 20M show a very “sharp” tuning.
For comparison with one EFHW Ignacio and me decided to activate EA2/NV-151 San Martin, full report here:
Activation was in a pleasant afternoon and we were on the summit until near the sunset, this time I could match in all band bands with DX QSOs on 20m too and excellent signals reports in 60M from Europe, just before QRT I tried to match 80m and it was possible at 1.5:1 swr, then called CQ few times in this band and one RBN in OK report me at 8dB We returned home very happy with the results…
Perhaps I could add more capacity on the output capacitor for better SWR in 80m but 1.5:1 is not so bad isn´t it? Also, I could do more tests with the 11.20M wire to match it in a reliable way on the 40M band. In any case this is an always open project.
I want to express my thanks to George KX0R for sharing with us comments and construction details of this excellent master piece which is his tuner design.
I enjoyed a lot building it and I´am very happy with the choice, this has given my portable station more flexibility and less weight.
See you all on the bands as a chaser or activator.