During JOTA 2016, my HF station had some RF issues due to the use of an off-center-fed-dipole (OCFD). This type of antenna almost always has common-mode current issues on the coax. Ultimately we solved it by making a 5 inch diameter coil of coax, about 8 turns. But prior to “fixing” the issue, Pete, W1LAB, pulled up his SUV and allowed us to use his Hustler 20m vertical. It worked surprisingly well — what we were hearing on the 135 foot long OCFD, 40 feet up in the air, was coming in the same S-level or better on a 4 foot tall vertcial antenna. Given those results I figured I needed to give things a try someday.
With my wife at work today and some spare time on my hands, I headed over to Compass Rose Beach and popped a 20-meter vertical on the roof of my truck using a 5-inch Hustler Mag-Mount. I did a bit of tweaking with my antenna analyzer and finally had about 3.5 inches of the whip sticking below it’s ferrule mount (the manual suggested 4″, which probably would have been spot-on).
This antenna produced the following SWR distribution:
14.000 1.5:1
14.100 1.0:1
14.200 1.2:1
14.300 1.5:1
14.350 1.8:1
Because this was just a quick experiment, I had chosen a MFJ 1620T over the Hustler due to lower cost ($15 vs about $65) and extended length used on the roof mount (7′ vs 4′). The single 5″ Mag-Mount is strictly a stationary mount — it would never hold the 7′ long antenna even at slow mobile speeds. I also had some RF feedback issues that were fixed by putting a 10-turn 5″ coil of coax right at the radio end.
I spent a hour on the air and worked seven stations in Spain, Saint Lucia, Bonaire, TN, FL, IL, and MN. The antenna performed well to the South as expected, as well as to Europe.
MFJ 1620T Vertical antenna on Hustler MBM mount – Jamestown RI dead ahead
Icom IC-7000 operating 20-m SSB. Powered by 30AH LiFePO4 Battery
Band conditions were just “Fair” on 20-m today.
