Good idea john
Ed
Very interesting ā¦ compact.
Last year I bought this tooā¦
https://www.ebay.it/itm/FILO-Aquilone-Aspo-A-CARICA-BOBINA-PRESA-RUOTA-200M-VOLANTE-attrezzi-Lock/183162409671?hash=item2aa55492c7:g:xMQAAOSwX3FaAque
Hi all,
I am currently experimenting with an improved design for my Superlight SOTA Vertical. The main problem with the current design, which the QRPguys base version will likely exhibit in the very same way, is that the SWR varies greatly with the type of ground and the exact deployment. In most cases, it is possible to get the SWR to an acceptable level by tuning the radial(s), but this can be a time-consuming process.
My current take (not yet implemented) is to
-
add a variable capacitor in parallel from either end of the inductor to ground and make that switchable with an on-off-on switch. By that the, simple loading coil turns into an L-match and can thus also provide impedance transformation, and
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replace the existing on-off-on switch for the 40-30-20m adjustment of the inductor by a tiny 8-position rotary switch and additional taps at the inductor so that you will always have at least one position with less and more inductance for 40, 30, and 20 m.
As for the inductor, I am inclined to use a small air coil (d = 20 mm, l= 30 mm, Nmax = ca. 40 turns) instead of the toroid, for (a) it will only be marginally bigger, (b) have a better Q (?), and (c) it will be easier to build a tapped version.
This version will make it unnecessary to carry an extra tuner and still be able to make the antenna usable under imperfect conditions.
Another option I am considering is buying a Miracle Whip antenna unit and replacing the whip by the 5 m radiator and a 5 m (or so) radial. The Miracle Whip design uses a variable autotransformer (i.e. a tapped inductor on a toroid with a variable tap position). The regular miracle whip antennas are often criticized for their poor tx performance, but that is largely due to the tiny radiator of 1.5 - 1.7. With 5 m on a fishing rod, performance should be much better.
Tuning with the autotransformer will be simpler (one dial). Many Chinese Miracle Whips now include a Tayloe SWR indicator, too, like this one:
What might also be interesting for others in the search for the ideal SOTA Vertical is this upcoming product from Wonder Wand. It seems to combine the idea of a tunable counterpoise/radial with a miracle whip matchbox and single dial:
See also here:
http://www.wonder-wand.co.uk/WonderWand/WW_Photos.html
73 de Martin, DK3IT
Iām interesting in hearing your results if you do this. I have the same issue with the existing design that you describe (variability in ground composition makes it fiddly to use). I havenāt used mine on an activation because of this.
73,
Joe // N0MAP
Wouldnāt performance improve if the loading coils were raised (perhaps 2-2.5m off the ground), rather than at the base?
Not sure whether you are replying to my message - if so: The problem is not performance per se. The problem is that the match to 50 Ohms varies so much with ground and deployment that the usage with a rig without ATU (e.g. MTR) may be impossible or harmful for the finals. Last week on OE/TI-002 I was using it with an Elecraft T1, which worked well. But the T1 is a bit bulky for my taste (in comparison to this lightweight antenna), another piece of equipment to forget, and potentially a single point of failure.
Martin
Round and round we goā¦
The oddball clone I made does 30/20/17/15 with no Wonder Wand components. Just wire, PVC waste pipe, 2x crocodile clips and a BNC connector. Cheap and repeatable on G/SP/OK/DM/OE/PA/LX/F/CT3 & EA8 summits.
Well, isnāt designing, building and testing new equipment at least half of the fun of amateur radio?
You use crocodile clips, while Robert Victor VE2ERY (now SK) designed a nice variable inductor mechanism
and used this as a nice autotransformer for matching a short vertical. I have also thought of using crocodile clips for tuning the loading coil of the vertical but am still looking for a better option. Rotary switches have been suggested in other āmiracle whipā designs, but you either need two of them or will have a very coarse adjustment. The best approach I have seen so far is that by G4FON:
http://www.g4fon.net/Musings.htm
BTW, if you have a picture of your design to share, I would be happy to see the details.
73 de Martin, DK3IT
EDIT: Credits for the image and info on VE2ERY goes to John, @VE3IPS - Miracle Whip Antenna Review | ve3ips
Moving away from the short vertical discussion, Iāve just discovered the work of Owen Duffy, who has done some interesting analysis on various aspects of end fed half wave antennas. Most recently heās released this write up (End Fed Half Wave matching transformer ā 80-20m ā owenduffy.net) on building a better broadband transformer for high impedance antennas. There are still some refining steps to go, and this transformer is only for the 80m-20m bands, but his research seems promising.
2 Likes
Just to say the effort in trying to get the QRP-GUYS loaded vertical stable - as in usable on a summit has come to an end and itās components are heading into the spares boxes in the workshop. I cannot recommend this antenna based on my experiences.
as always YMMV.
73 Ed.
Hi Ed,
are you using a tuner-less rig (e.g. FT817 or MTR) or one with an auto-tuner (e.g. KX-2)? I think that with a tuning component, the basic approach is well usable on small summits, although I think that an air-coil with a higher Q will not make the design dramatically larger.
Will post details on my V7 approach with integrated L-Match as time permits. I also did a WSPR comparison with a full-sized EFHW with traps. On 40m, performance is comparable when used with a single but tuned radial. The main problem is the high directivity and the low angle of radiation, which may mean you canāt get OE/HB9/IT/DE-BY contacts from a summit in the Alps.
73 de Martin, DK3IT
Sadly my experiences are the same as Edās. Getting the antenna to work on 40 has been my biggest issue. The ground radials and the effect they have to propagation is a bit of mystery too me as well.
I have continued to use mine successfully, more so than any of my other sota antennas.
First a perfect match on 20m is a must. Try 30 and 40 and make sure your swr is ok there. To me less than 2:1 is perfectly fine, as it should be for most. Iām under 2:1 though as is with both bands. If you have an issue with either band check your torroid winding count and spacing. I paid extra attention to both. Some have had to adjust the number of windings but I have not.
Iām also using 8 radials with mine, which has greatly improved the swr stability. At 26 guage this is not a noticeable increase in size or weight.
I get 2:1 on 20m and 30m. But I canāt get 40m below 5:1. I even took out two windings which did help, but not enough. Perhaps Iāll add more radials.
You should be able to get 1.1 to 1 on 20m. Do that by changing the element length. That is the key.
Copy that. I ended up putting it on an analyzer and can bring it down. 40m wonāt dip below 4.1 though.
Are you resonating low or high on 40m?
Its high on 40m. I ended up taking some windings out checking the SWR on my analyzer with each removed wrap. Went from 5:1 to 4:1. 20m and 30m are still rock solid.
Josh, I watch/subscribe to the channel by the way.
Just to make sure (Iām not questioning your intelligence), you have both switches moved over to the 40m position right?
Also, wouldnāt you want to add turns to lower the SWR if 40m is resonating high? Or am I thinking backwards here?