Adding Radials to a Mag Mount

Reading through some blog posts recently, I came across an interesting idea from John AE5X. In the comments section of a recent post, John mentions adding a ground stud to a magnetic mount. The ground stud allows him to connect two ¼-wave radials (for 20M) for his MFJ-1979 telescopic vertical. So what follows is my implementation of John’s clever idea. 

On occasion, I’ve used my Gabil GRA-7350TC vertical with a small magnetic mount salvaged from an old 2M/440 antenna. I plan to use this configuration on my (far) better half’s car while visiting family over the holidays. The mag mount is only 3.5 inches in diameter, so I’m sure it’s not providing much of a ground connection. While the Gabil vertical is certainly usable with this mount, I’ve always felt that it needed more of a counterpoise on 40M and 30M to obtain a better match. I figured John’s idea might be the way to go. 

Since I needed to drill a hole from inside the mount, I had to remove the foil covering from the bottom of the mount. This magnetic mount is probably around 25 years old, so removing the foil wasn’t too difficult. Using my pocket knife, I was able to peel the foil off, while keeping it intact. 

Next, I drilled a ⅛-inch hole through the ground plate and out through to the top of the mount. It was a tight squeeze, but I was able to get a 4-40 bolt and a star washer in there. On the outside of the mount, I used a nut and lock washer.

The final step was to re-apply the foil covering on the bottom of the mount. I used some rubber cement to reattach it. I don’t know how well the rubber cement will hold up over time, but it won’t be seeing heavy use. It seems fine so far. 

While I was at it, I replaced the PL-259 connector. The years had not been kind to the connector that was on there. 

I gave the modified mag mount a try during a recent activation at US-1380, KFF-1380. I used the GRA-7350TC and mag mount on the roof of my truck. With no counterpoise wire attached, the best match I could get on 40M was just a hair under 3:1. 

Next, I attached a 33-foot counterpoise wire to the mag mount. I ran the wire off the back of the truck and onto the ground. To avoid creating a trip hazard for others, I wrapped the wire around the side of the truck. In this configuration, I got the SWR down to about 1.2:1. Success!

Using the same counterpoise, the best I could do on 30M was a little under 2:1. I tried two 16.5-foot wires, but the result was about the same. No worries. An SWR of 2:1 is a piece of cake for the Elecraft T1 tuner. 

I ran the entire activation on 40M and 30M with great results (40 contacts in less than an hour). In fact, it was the best I have done with the Gabil antenna and mag mount. Was it because of the counterpoise wire? Maybe. Regardless, my five-watt signal was getting out just fine with this thing.

Thanks again to John AE5X for the inspiration.

72, Craig WB3GCK