By Rob Ramsey, AH6X
I recently purchased and received an Elecraft AX1 antenna. Since then, I’ve tested it and made two significant modifications that I found helpful and wished to share.
Though the stock antenna configuration works as advertised, through experimentation, I have discovered it is possible to make it resonant on 10, 12, 15, 17, or 20m.
Elecraft markets the AX1 as a field expedient antenna that supports operation on the 15, 17, and 20m bands with a tuner. Some tradeoffs were made as packaged: a single 13ft radial, the 46.25in whip, and a 20m/17m switched coil assembly. The stock configuration lives up to its branding and delivers an experience proportional to its compromises. However, more is possible.
The AX1’s vertical element is too short to be resonant on 20m. This limitation can be overcome by adding additional coil or by using a slightly longer whip antenna.
The single radial is a similar situation; with a 13ft length, it’s not resonant on any specific amateur band. A multi-element radial could be used with resonant lengths for each of the desired operating bands. These trade-offs were probably made for a variety of reasons.
First, using this antenna in a resonant multi-band configuration requires an antenna analyzer to tune the whip length properly.
Second, using a longer whip and multi-element radial would increase the cost.
Third, a longer whip and multi-element radial weighs more and would take up more room than the stock parts.
Fourth, a longer whip is less stable when mounted to a small tripod or the radio.
Lastly, tuning the antenna and fanning the radials out would take longer than the original deployment strategy, diminishing the antenna’s field expediency.
Given a choice, many radio amateurs will choose an antenna analyzer over a tuner. Over the last two weeks, I’ve created and tested a 15/17/20m multi-element radial and, with the help of Jon (KG7KMV), an antenna adaptor for the AX1 coil assembly.
The multi-element radial has been cut per the standard calculations (see charts at bottom of post), and the adaptor allows me to connect any 3/8-24 threaded whip to the 4mm x 0.70 threaded coil assembly.
The BuddiPole product line has a large variety of telescoping whips. For this project, I used their Featherweight whip, which extends to 72in (6ft) and collapses down to 13in. With it, the antenna can be easily tuned by collapsing or extending the telescoping whip.
For the multi-element radial, I used Super Antenna MS135 SuperWire with a 14-16 AWG spade connector and some heat shrink tubing. For storage, I wrap the radial around a SOTABeams wire-winder.
This custom configuration allows for a 3:1 SWR in the 10, 12, 15, 17, and 20m bands. Overall, I really like the Elecraft AX1 antenna. It’s a good product, made resonant, with just a few adjustments. See images below.
I also made a "tool roll". My mother-in-law showed me how to sew a wrench roll for my Elecraft AX1 antenna. I use a similar setup for my Super Antenna. The fabric is light, protects the parts, and makes antenna transport easy.
Let me know what you think in the comments. Thanks in advance!
Rob, DE AH6X.
Many thanks for your contribution to the Blog Rob!
A very interesting read. I love this sort of stuff.
Tom, M7MCQ.
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