I own three antenna tuners. Two of them are SGC’s SG-230, and I’ve been using one of them at home for a while. The other one was on auction as a new one for a pretty low price, so I thought I could sell it for that much, and after bidding a little higher, I won it easily.
The third one is an ICOM AH-4. This AH-4 is small and doesn’t support 1.9MHz, but it can also be used for 50MHz, so it’s suitable for mobile use. On IOTA vacations, I took it to various places, including T88, 8Q7, V63, FO8, VK, and KH2-6-0.
The key to this type of operation is to be able to install it anywhere and to be able to transmit on any band. To achieve this, you need to distinguish it from an antenna system that relies on earth.
The AH-4’s instruction manual says, “Do not use elements with a length that is an integer multiple of half the wavelength of the frequency band being used.” As an amateur, I would assume that a one-wavelength loop antenna is a half-wavelength dipole, and think, “Well, for a loop, it should be double that, but an integer multiple of one wavelength is no good?” However, this antenna tuner is for unbalanced antennas, and the earth side does not match anything.
Somewhere in a book I read, “When using a loop antenna, avoid odd multiples of half a wavelength.” I am not familiar with antenna theory (lol), so I thought that if you imagine the distribution of the current antinode, it might be true. I decided to follow that to reduce the risk of damage.
The shortening rate for the 3.5MHz band seems to be too large, so I will exclude it here, and look for a suitable loop length in the 7 to 28MHz range.
It seems that 13m, 17m and 20m will avoid “odd multiples of half a wavelength” for any frequency. Taking into consideration the length of the fishing rod I have, I decided on 13m.
…Actually, that’s how I made this antenna for a private station around 2000, and this is a reproduction of it this time.
I also used the telescopic pole I used for IOTA. The spreader mount uses the mount part of a ready-made V-shaped dipole. It’s lightweight so it won’t fall over…or so I thought.
The day after the typhoon, I got a call from a club member saying, “The antenna broke!”
Tragically, the glass rod broke at the base. The part that has just lost its rigidity is the first to be damaged. But thanks to the element that connected the rod, it didn’t fly all over the neighborhood. It was a close call.
…. Not giving up, a few months later I bought a new spreader and rebuilt it. I tried to make some adjustments so that the rigidity wouldn’t change so suddenly.
In fact, when this fishing rod bends, the tip is restrained by a triangular element, and in the past, the thin part of the rod just next to the eyelet in the illustration has broken.
For this reason, we filled the tip of the rod with a slightly less viscous adhesive.
Well, it held up for the next four years, so I guess the reinforcement was effective. (Thank you for your hard work.)
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