My telescopic antenna is 5.6 m long and usable from 40-6 m with an antenna tuner. Such telescopes are available cheap at AliExpress.
73, Peter - HB9PJT
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Taking this interesting thread slightly sideways, I have a question…
Conventional wisdom (eg my 1971 RSGB Radiocommunications Handbook since when things have no doubt developed) suggests that the loading coil in electrically short loaded whips (eg mobile antennas) can contribute significantly to the radiation.
I think that torroidal inductors have a closed field, and tend not to radiate.
On the other hand, they can have a higher Q than a solenoid coil, which suggests lower loss in the inductor and more energy to radiate from the whip section…is that why they work well in the AX2 design…?
Adrian
G4AZS
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I assume that every coil radiates, even those on the toroidal core. The whole antenna can consist of one coil (helical antenna) or the coil is very short (toroidal core) which radiates much less.
73, Peter - HB9PJT
Closing the loop on this one: I completed the AX2 mod today and I’m happy to report that it was very straightforward, if a little delicate. The results are exactly what I had hoped. Very low SWR in the 10m CW range and my KX3 brings it down to 1:1 across the band.
I know there are cheaper routes to a portable 10m vertical, but there’s a lot of anecdotal evidence to suggest that this one punches above its weight.
Incidentally, I did try to use the KX3 ATU on the unaltered antenna to see if I could make it usable on 10m, per a recommendation from Etienne-K7ATN, but could only bring it down to 3.6:1.
Thanks for the encouragement. I’m always impressed by the helpfulness of the SOTA community.
73, Steve-W7ETF
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“Conventional wisdom suggests that the loading coil in electrically short loaded whips can contribute significantly to the radiation”.
“I think that torroidal inductors have a closed field, and tend not to radiate”…
Partially answering my own question from higher up the thread, apparently it depends on the permeability of the core material:
https://owenduffy.net/balun/concept/FluxLeakage.htm
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I am also pretty happy with various short vertical designs for SOTA.
When it comes to performance, I think it is important to realize that the pattern of radiation in relation to potential chasers is likely more relevant than absolute radiation efficiency, and there will be a lot of randomness involved.
At least when activating a rare summit like e.g. the Matterhorn, all you need are a few random good paths to a few chasers, including all kinds of reflections on etc. So what a short vertical looses in terms overall performance may not really affect the number of QSOs in the log or the success of the activation. They will just be distributed less evenly in terms of their QTH.
The expected number of QSOs per activation is IMO a function depending on
- duration of the activation,
- number of chasers QRV or motivateable to be QRV (e.g. weekends vs. during the week),
- mode / set of modes,
- attractiveness of the summit (points, rareness,…),
- radiated power,
- match between radiation pattern and spatial distribution of chasers,
- propagation and condx in general,
- QRM/contests competing with our signals,
- effort and chances for chasers (time vs. likelihood of a successful QSO, alerts and spots and quality thereof - e.g. precision and reliability of forecasted information; competence of the operator managing the pile-up, …),
and finally - the radiation efficiency of the antenna.
73 de Martin, DK3IT
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Owen Duffy describes the shielding of magnetic flux. In the case of the antenna, the electromagnetic radiation is of interest, which is not the same.
73, Peter - HB9PJT
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Hi Martin,
Yes!
I didn’t mean to hijack this thread (*), but it links with my thinking about SOTA antennas for 160m, where any practical design will be a compromise - too low, too short, poor counterpoise, high angle of radiation…
I’m not an academic or an engineer, but I’d like to try and improve my understanding of theory - empirical experiments with large quantities of wire are fun, but can take up a lot of time and results are at best questionable!
(*) If I come up with any more results or questions, I’ll maybe start another thread,
73
Adrian
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Just to support my claim:
My Up-and-Outer on the Matterhorn seems to have had a pretty directional radiation, likely due to the two short radials hanging in that direction (source is here):
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Damn Heinz, thats exactly what I want to build!
Why did u use T68-6 toroid? Can I use also xx-43 toroids?
Are some capacitors also necessary? Saw the mhw-4217 and he is adding a varicap.
So in conclusion I want build a AX1, for 40m, 20m and adding maybe some other bands.
Thx a lot!
73
Julian
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I would say no. Iron dust cores, such as -6 mix, are used to make high-Q inductors. Ferrite cores, such as -43, are used to make wideband transformers or chokes. They are not really suitable for inductors.
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okay thx good to know!!
73
Julian
The toroid in the AX2 as pictured by @W7ETF Steve is an unusual one, it’s painted to indicate -6 material but has the height of about four T-50-6es all stacked. Any idea what this is? It seems that other short base-loaded whip experimenters have had success with conventional T-68-'s…
The original coil core looks like a T51-6 (e.g. Micrometals).
In order to avoid the somewhat tricky soldering work during the modification due to the limited space and to enable a problem-free fine spread of the windings to set the desired resonance frequency, I use 2 stacked T-50 toroidal cores as a “replacement coil core” (Mix #2 for 14 and 18 MHz, Mix #6 for 21-28 MHz), wound with ECW 0.63 mm (AWG #22).
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By the way,
The improved stability of the BNC connector on the AX2 compared to the AX1 motivated me to “retire” my AX1.
My small (finger … and backpack friendly) loaded all-band antenna with the existing 60/40/30 m extender includes now
-
AX2-20 (for 60/40/30/20 m)
-
AX2-17 (for 17 m)
-
AX2-10/12 (for 10/12 m and (together with LC30m) 15 m)
-
2 guyed radial pairs of 2.5 m (for 17-10 m) and 3.1 m (for 60-20 m)
-
Tripod (for all seasons/earth surfaces …)
-
Selfie stick allowing a feed point height of approx. 0.85 m
Note: I noticed with my AX2’s (when new) that the hexagon nut on some examples was only tightened hand-tight and in one case it was even loose. The result of this: The antenna wobbles about like the AX1 or a little more …
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Heinz did u print the cases with your 3D printer or are these the original plastic cases?
73
Julian
… if I remember correctly, there is no 3D printer in our household …
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Ahh okay got it haha.
It looks easy to make the antenna with an 3D printer and a BNC plug.
How is the performance of your AX2? Did you made “good contacts”?
73
Julian
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Dear Heinz,
Your neat whip antenna extenders, as for any of your homebrew gear, are precise as a good Swiss watch!
Thanks a lot for sharing your detailed info. I also like that tripod which seems to be lighweight as well.
I’m in the process of building something similar here. Christmas will bring me a whip to play a bit with…
73 Ignacio
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Thank you Ignacio.
The main motivation for building this little and, above all, very handy antenna came from the fact that my fingers/hands had been plagued by tendonitis over the last few years and required some annular ligament operations (still a few pending …).
I hope to see your smiling face soon when your short whip also captures the signals from well-known SOTA dx stations (e.g. from ZL, JA, PY, LU, W, VE, …).
For my part, I would also like to use my little whip to try to exceed the previously achieved distance of 992 km for an s2s QSO in the 60 m band, hi.
73 gl, Heinz
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