Antenna Tuner is Too Smart

Automatic antenna tuners are great. Just tune your radio to the frequency you want, flick the TUNE switch, and you quickly get an optimum match between your rig and the antenna. Well, not always. I have an ICOM IC-7000 with an LDG AT-7000 antenna tuner. This is a great little tuner, but it sure tricked me this time.

I wanted to try my rig on the 6 meter band for the first time. So I set up the station and was listening around for signals during this weekend’s VHF contest. There are some CW beacons I had heard before, so I tuned to that part of the band, activate the tuner, and heard nothing. Then I hit the TUNE button again, bypassing the Tuner, and the beacon suddenly appeared! So I hear no signal with the Tuner doing the matching, but I hear the beacon when I bypas the Tuner.

After noticing that the SWR was indeed lower when the Tuner was inline, I realized what was happening, The Tuner has many memories. If it found a “good” match at a frequency, it uses that information to shorten the tuning cycle next time you go to that frequency. The Tuner had apparently found a match that provided a low SWR, but it also resulted in a lossy signal path. The instruction manual showed me that I could go into the Tuner case and push a switch that would force it to retune, even though it thought it had a good match already. So I pushed the button, the relays clacked, and presto, a good match and the beacon reappeared. Guess this button should be on the front panel! Then I worked my first 6 meter station ever.

Passing of L.B. Cebik

I just heard that L.B. Cebik has died. The amateur community has lost a real antenna expert and a prolific writer. I never knew L.B. but have spent many hours on his website reading his articles, and using his antenna models.

He recently published an interesting article about a short-boom yagi for 6 meters. I wrote an e-mail to him telling him that I found the article interesting, and was thinking about building the antenna. However, I really did not want it for the wide bandwidth that he had in mind. My application was more to leverage the small antenna profile for a high-wind environment. In a day or two, he responded with a slight redesign of the elements to maximize performance in the portion of the band I needed.

Sorry I never got to meet the man, but I know he will be sorely missed in the amateur community.

Half Square Array

I’ve been looking for some new wire antennas to try. The Half Square (HS) looks interesting. It is two 1/4 wave vertical elements, with a 1/2 wave horizontal element connecting them. The ARRL Antenna Book has a writeup that looks interesting. I really need something cut for 20 meters and this might be worth trying.

The HS is usually fed at one of the top corners with coax. One benefit is that it is forgiving to symmetrical distortion of the design (like bending the legs due to mounting restrictions). The downsides are that it is high-Q (thus narrowbanded – bandwidth is less than a dipole) and it appears to be a primarily vertical polarity antenna. L.B. Cebick  provides a model of the HS for EZNEC (along with anything else you could ever want to know about antennas). 

What really makes this antenna interesting is the fact that it can be built as a 2-element array (or wire beam). This is attractive to me due to my operating QTH, where only the water is to my East. In any US-based operating, I want to push more of my power to the West. I may also mount it close to the ground, to improve NVIS performance for QSO parties.