Well done Tim and Shadow, keep it up!
HNY 73, Heinz
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Am 07.01.2025 um 10:26 schrieb Tim Morgan via SOTA Reflector reflector@sota.org.uk:
Hi Heinz,
Now that the 10m challenge is complete, i would like try you all-band inv-L antenna GP antenna in particular as its multiband and gives better performance on the higher bands than my EFHW. Thank you for your document. Very useful.
I note that you have to have a matching circuit for 20m. This looks like it matches the impedance for 20m and so presents a very good SWR to the radio. (NOTE: I am not interested in 60m or 80m).
I would like to understand, why not just use a 9:1 unun and let the KX2 tuner do the rest ? Did you try this ?
I apologies in advance is i have missed something…
Thanks
Tim
Am 07.01.2025 um 14:40 schrieb Bluewin heinz.baertschi@bluewin.ch:
Hi Tim,
Your question “why not just use a 9:1 unun and let the KX2 tuner do the rest?” may be justified, but looking only at the VSWR of an antenna is, in my opinion, far too trivial to understand how well and in which direction an antenna really radiates.
The design of the 10.90 m multi-band inv-L antenna (a bent vertical antenna) was therefore a pure “EZNEC drawing board antenna”, in which initially only the radiation characteristics were optimized across all bands. It started with a wire length of 11.20 m, but this required external matching aids for the KX2-ATU on 4 bands (-> 4 switches).
The final 10.90 m long inv-L antenna required, apart from the loading coils for 80 and 60 m, only the impedance matching of the 20 m band (~ half a wavelength …), “the rest was done by the KX2 tuner”, hi.
For this impedance matching, a 16:1 transmission line transformer was initially used, which was later replaced by a 9:1 transformer of the same type (FT-82-43 ferrite core).These solutions worked without any problems.
Later, the slightly more efficient version with the 20 m L-Match was used. It was a good feeling to be at this state of the art … This version is currently uploaded to HB9SOTA.
BUT, because Bruno, HB9CBR, had problems with impedance matching on bands other than 20 m with the KX2/3-ATU over the years at summits that did not allow for textbook antenna installation, I have been building the old solution with the 9:1 transmission line transformer again since last year (Appendix). As a developer purist, this took some effort on my part, hi.
All’s well that ends well for everyone.
Note: The antenna achieves best performance at an apex height of 6 m (or close), 5.5 m is already a compromise.
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A possible optimization from a technical and practical point of view has also emerged over the years with regard to the radials (Appendix).
By the way, I have been thinking about updating the document published on HB9SOTA for some time because the 10.90 m multiband inv-L has become my standard portable antenna and it is also used by some other SOTA/WWFF/POTA enthusiasts.
I hope you continue to have fun with portable radio.
73, Heinz HB9BCB
And finally, Tim’s handsome version