Antennas: a Riddle Wrapped in a Mystery Inside an Enigma

I owe the title of this post to Sir Winston Churchill who once used it to describe a country that is prominently in the news at the present time. It seemed an appropriate description for ham antennas too because the more I know about antennas, the more I realize how much I don’t know. Maybe even what I think I know already isn’t correct. What I do know with absolute certainty is that I will never stop learning about antennas until the day I join the choir invisible.

If the shack sloth experts are to be believed, it matters not how many rare DX contacts you have made with your antenna, it still isn’t a “good” antenna until they have analyzed and declared it so. Perhaps we shouldn’t be so inquisitive. Why not just pop along to your local “candy store”, pickup a pricey packaged antenna and don’t question the manufacturer’s claims about gain, F/B ratio, “resonant on every band” etc. Ignorance is bliss.

If you have read my recent posts you will know I am on a quest to find a rapidly deployable, field expedient antenna that has a small footprint and low impact on the environment. “Long Tall Sally” checked all the boxes – until it fell over in the wind. Recent experiments have been greatly enhanced by the acquisition of a RigExpert AA-55 ZOOM antenna analyzer to replace my squinty, fragile nanoVNA.

The nanoVNA is a cheap and wonderful little box of electrickery, but there are a couple of things I don’t like about it. Regrettably I chose the model with a tiny little screen that my septuagenarian eyes struggle to read. Secondly, it has fragile sma connectors that are directly attached to the circuit board. Since nearly all my coax cables have PL-259 connectors, an adapter is necessary. I have not had much luck with adapters. The RigExpert box, on the other hand, has a nice big chunky SO-239 and a clear bright, color display.

RigExpert is a Ukrainian company (which surprised me) – I call my AA-55 ZOOM my Ukrainian friend. The AA-55 ZOOM is an HF only device (other models are available with wider range) but that suits my needs, I rarely venture into VHF/UHF. Anyway, after much cutting, drilling and grinding in my garage workshop, my Ukrainian friend and I have come up with a new antenna design that works fine business. I christened it the “Enigmatenna”. It hasn’t been blessed by the shack sloth experts, but it has excelled in the field.

The radiating element is a 7-section “tactical” whip that I have written about previously (refer to my “manpack” series of posts). A base loading coil of 2.6 microhenries brings the SWR down below 1.5:1. The feedpoint is 5 feet above ground, supported on an aluminum pole held up by a highly modified photographic tripod that I bought about 50 years ago when SLR photography and fumbling around in a darkroom with dubious chemical substances to develop, fix and rinse rolls of film and 16×20 inch black and white prints was my passion.

Every Day a New Surprise!

Initially I was convinced that the tripod not only supported the antenna, but was actually a fundamental part of the antenna – that it comprised the radial system. In the real world, where the RF hits the ionosphere and comes crashing back down to Earth – along with my ill-advised illusions – things are completely different. As I discovered when I took the Enigmatenna to a local POTA park (CA-0184; formerly VE-0184 – Craigleith Provincial Park, Ontario), the tripod performs no other function than to prevent the antenna from falling down.

Incidentally, this is the same park where I once arrived without an antenna, but managed to complete a POTA activation by improvising. You can read about that experience here.

If you take a look at the image below, you will see the metal footpad at the base, in the center. I had removed the footpad and replaced it with a rubber leg tip for the activation. As I set up my POTA station and checked it with my RigExpert “Ukrainian friend“, the SWR had jumped from 1.5:1 to 2.5:1. It was getting a bit late in the day so I made a mental note to investigate further back at the home shack and proceeded with the activation. My L-match soon took care of the slight mismatch, but not before another gremlin had intervened to confound me. A wire had become detached from the paddle jack in my QROp manpack. Fortunately I carry a tool kit in the truck and my trusty Weller butane-powered soldering iron soon restored the connection.

How Did the Enigmatenna Perform?

The activation went well – despite my brain being in a frazzled state following the long and difficult setup. Propagation conditions were good and the POTA hunters were on the air in full force. I battled through a pile-up that lasted through 31 QSOs including 2 park-to-parks, 1 Alaskan station, 2 Europeans and a hunter in Puerto Rico – all with 20 watts CW. I would say the Enigmatenna earned its spurs that afternoon.

The next day I investigated the ground plane enigma a little further. I believe the aluminum support pole is providing a capacitive connection to ground. The connection can be enhanced by attaching the steel footpad resting on a small sheet of hardware cloth. A 6ft length of aluminum duct tape was also tried and worked equally well (as evidenced by lower SWR).

What About Radiation Efficiency?

It is very difficult to measure radiation efficiency without professional test facilities. An antenna doesn’t radiate all the energy supplied to it through the feedline; some is wasted as heat due to ohmic losses in the antenna. Careful attention has to be paid to all connections in the antenna to ensure there is as little resistance as possible. The Enigmatenna is a simple structure but still involves points at which threaded components come together, and in which copper, aluminum and steel are joined. One “gotcha” when using aluminum tubes is anodizing. This creates an oxide layer on the surface of the tube to protect the metal – but also puts the kibosh on its electrical conductivity. Even “Stainless Steel” comes in different grades, some of which still allow some rust to develop.

And What About the Design Objectives?

The purpose of the exercise was to come up with an antenna that is rapidly deployable, field expedient, has low impact (i.e. no disturbance of trees, no stakes in the ground) and stealthy. Several dog walkers passed straight by me during my activation with the Enigmatenna so it passed the stealth test. With a little more work to improve the ground plane arrangement, following the learning experience during the activation setup, this one is going to be a champion. Now, as I continue to develop my antenna modeling skills, maybe one day I will truly understand why it works!

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