Standard 102" mobile whip on a ball mount. The only thing slightly different here is the SGC SG-237 Smartuner used to match the whip. The whole assembly slides into the trailer hitch. I can remove it quickly if I (or my wife) don't want the "ham radio look" for a while.

2003 update: There has been an update since I completed this installation. It looks good but it just didn't put out much of a signal. Other hams told me that the other fellow who drove to Dayton at the same time who had a Hustler was always stronger than me (Don, W0DM). Therefore, I have since removed the Smartuner and whip and replaced them with a Hustler. I am having good luck with the Hustlers.

I wanted to know why so I read everything I could find. One of my best sources has been Jerry Sevick's Building and Using Baluns and Ununs. The title is misleading because in the appendixes Dr. Sevick included his work on short verticals. (2008 update: Dr. Sevick has published that work separately in a small book, The Short Vertical Antenna and Ground Radial, Sevick, CQ Communications 2003.) It is clear that base loading is very inefficient.

According to Bill Wrinker, W6OAV, there is a 2db loss just by moving the loading coil from the center to the bottom. But I suspect the real killer is not that 2db, but what happens to the radiation resistance when the coil is at the bottom. It drops to such a low value, 2 ohms, that it is practically impossible to get a good enough ground system on a car to prevent tremendous losses. Maybe ground losses in a mobile installation could be 10 ohms. I am convinced that this low impedance is what did me in.

2008 update: I sold the SGC tuner at a hamfest and the fellow who bought it determined the unit is defective, with the help of SGC tech support. This new fact taints everything I have written above. Was the tuner bad when I was using it or did that happen later? If I get the time, money, and inspiration, I will revisit this whole installation with a new tuner.

2009 update: I wanted to know about short verticals so I dug up a lot more reading. Turns out the radiation resistance of a 102" whip is MUCH lower than I said above. It's more like .87 ohm on 40 meters. Ground resistance is maybe 15 ohms. You can see the effeciency is going to be VERY low, like maybe 4 per cent. That means if your transmitter puts out 100 watts, this antenna is radiating 4 watts of it. The rest is heating up the ground and the loading coil.

A top hat has the lowest loss of the various loading techniques. Putting a top hat on the mobile will help another 2.5 db, in addition to gaining the 2 db from raising the loading coil from the base to the center. Another change I have made from the original is to remove the SGC tuner from the base of the whip. It did a good job of matching the .87 ohms of radiation resistance, 15 ohms of ground loss, and maybe 10 ohms of coil loss. The problem lies in the low efficiency of my design.

Upon studying Walt Maxwell's Reflections II I understand that there is no gain by putting the tuner at the base of the antenna. As long as I establish a conjugate match, it doesn't matter where the match is physically located. Therefore, a tuner inside the vehicle is easier and cheaper. Ideally I can get the antenna impedance within an acceptable range for the internal tuner in the transceiver.

My next effort is to build a loading coil better than the Hustlers. I will shoot for a Q of 300 with very low distributed capacitance. I plan to do this with wide space 14 guage coils with a diameter twice the length. Another upgrade is to add a top hat. Although I have built top hats, physically they are not too great. I like the designs of a top hat sold for screwdriver antennas made by DX Engineering.

Finally, I plan to use large diameter tubing to reduce loss and increase bandwidth. Wind load is the tradeoff. I figure the perfect diameter is about 2 inches, like the lower part of a screwdriver. Above the coil I plan to use a Hustler mast. That will mate with the DX Engineering top hat.

My final design improvement involves placement. When the whip is near the ground like it is now, the ground loss is higher. Getting the antenna as far away from the lossy ground as possible will help. A car is a poor mobile antenna vehicle. A bread truck would be just about right, or even an 18-wheeler if you could put the whip on the roof. Too bad there are bridges to clear.

I will attempt to get the antenna as high as possible on the car, maybe on the roof, keeping in mind that I have to clear overhead obstructions. I could use a magnetic mount on the roof IF I could find a good ground connection. Since I have a moon roof there might be a screw somewhere that I could use for an electrical contact to the sheet metal. I will probably need a nylon fish line guy system to keep the wind from blowing it all away. "

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