I was on the brink of pulling the trigger on the purchase of a new automatic antenna tuner for my portable rig recently, when something unexpected happened that slammed the brakes on the acquisition.
For a few weeks I have been operating my Yaesu FT-891 with an LDG Z-11 automatic antenna tuner, but there are two problems with that arrangement. First, and most importantly, the original LDG Z-11 is a QRP tuner. That’s fine and dandy, especially since LDG’s interpretation of QRP stretches to 60 watts for CW. But if I were ever tempted to jiggle the HF power up just a little too far my CW signals would turn into smoke signals.
The second issue is related to the Z-11 firmware. For some reason known only to the wise men in LDG’s engineering department, the automatic tuning only kicks in if the Z-11 sees an SWR greater than 3:1. Most of my field antennas have a native SWR of less than 3:1. The original Z-11 does not permit that threshold to be changed by the user (unlike later models).
Now call me a confused cynic if you will, but driving a QRP (or any other) signal into a 3:1 SWR results in a 25% power loss. Okay, I know that struggling to make contacts during bad propagation conditions is all “part of the fun of QRP”, but how much fun is enough?
So, I have been using my Z-11 in manual mode. That means keying up the radio and pressing the [TUNE] button on the Z-11. In every case my faithful, but ancient, Z-11 finds a 1:1, or very close, match. That’s what I call a manual tuner! The only difference between the Z-11 and a good old fashioned, honest to goodness box of variable inductors and capacitors with knobs on, is the Z-11 can find a match much faster than the latter. There is an old joke often told up here in bear country; a bear can always outrun a human, but no problem, you don’t have to outrun the bear, just the person you are with. LDG’s Z-11 tuner is like a bear in a black box.
Problem – 1:1 SWR!
Now, believe it or not, the Z-11’s ability to always find a good match can also be a problem! Let me explain. I set up my my portable (should that be POTAble?) antenna outside in the Big Blue Sky Shack recently, laid out my usual four 13ft radials and keyed up. Oh, I know 4 radials just ain’t nearly enough to satisfy the armchair experts out there. Efficient, or not, a few thousand entries in my log say “yeah, but it’s good enough for a rapid deployment portable antenna.”
But where was I? Oh yes; I, keyed up my rig, pressed the [TUNE] button on the LDG “bear in a box” and mere seconds later I had a 1:1 match. Just what I had come to expect from my grey-haired old tuner. But wait, there was a problem! I was about to spin the dial to find a station calling CQ when I casually looked over at my antenna.
The purpose of the exercise that day was to find out whether a quarter wave vertical antenna mounted on a spike very close to the ground would perform as well as the same antenna mounted on a short pole. The short pole I had been using up until now is a repurposed aluminum ski pole. It’s sharp end penetrates the soft summer soil and can hold a 17ft whip upright even in a wind.
A Short Sharp Shock in the Shack
I wanted to leave the pole at home and use a short spike instead. The spike is a modified 12-inch steel tent peg. Something deep inside of me said this ain’t gonna work. The feedpoint of a quarter wave vertical is a high current point and a high current point is where most of the radiated RF emanates. Surely the surface of the planet would suck up my meager offering to the ionosphere leaving little energy to make the trip into space.
I modeled both the tent stake and ski pole supported options in EZNEC. The far field propagation and gain were the same in both cases. I thought of the mighty AM broadcast towers on the outskirts of my home town. I thought of my code buddy’s full-size 160m quarter wave vertical antenna. All those towers were radiating elements mounted close to the ground (albeit with hundreds of radials). But still, I had to try it for myself to become a believer, and that meant I needed at least one QSO in the log for verification.
So, I looked over towards where I had planted my vertical whip expecting to see the tip about a yard shorter than usual. But I was horrified by what I saw – nothing! In my haste I had forgotten to raise the telescoping whip. By all the ancient Norse gods (I am descended from Vikings), my hard-working little “bear in a box” told my radio that the antenna was good-to-go when it was in fact decidedly ungood-to-go.
I could have happily transmitted into that stubby little whip, without causing any grief to my rig’s finals and, in all likelihood, gotten precisely zip, nada contacts. It just goes to show you that I may be a lot slower finding a match by twiddling old-fashioned knobs, then checking for any mistakes the tuner can’t detect, but I’m smarter than the average bear.
Wet Noodle? Not a Problem!
Okay, I know, I could have made exactly the same inattentive error while manually tuning with a good ol’ box with knobs on the front panel. And I may still buy that new automatic tuner. But, here’s the rub (as Shakespeare might have commented if he were alive today), you really can’t be lazy and expect an automatic tuner to do all the work so you can just sit back and make QSOs. An automatic tuner’s job is to find a good match – at lightning speed – to whatever antenna you connect. It doesn’t care whether you are working into the finest example of highly efficient RF engineering – or a wet noodle!
Ham Radio Outside the Box 