Diamond NR770HB antenna on two different mounts

Or how I damaged the first mount and replaced it with a different one

Photo by Skitterphoto: https://www.pexels.com/photo/snow-covered-car-58098/

Selecting an antenna for a new vehicle

We got a new vehicle recently and I found that my dual-band mag-mount antenna just didn’t work well. What does that mean? It means the door seals let water pass wherever the coax passed through. Having a wet floor in a new rig is not my happy place.

I spent some time looking at alternatives. The vehicle is a Honda Ridgeline truck with a tonneau cover. I found surprisingly few places to mount an antenna without drilling a hole in the roof. Having had several vehicles with roof leaks, I’m generally opposed to punching a hole in a perfectly good roof.

I looked at the bed of the truck but with the tonneau cover, there weren’t good options. At that point, I was thinking of a magnetic mount or a permanent mount but also recognized that I probably wouldn’t get a good ground plane with anything in or around the truck bed.

Next, I looked at the hood-fender seam to see if it was wide enough to custom fabricate a fender mount. Nope. That seam is tight. I did consider fabricating a plate to bolt to the cross-member above the front grill, with the plate extending forward beyond the lip of the hood. I think that would be doable, but going down that road would be a lot of work. Maybe, I thought, there is an easier way.

Meanwhile, I was also talking to my local ham friends about what they had done. As you might imagine, there seemed to be infinite ways to mount an antenna. I kept coming back to what I thought was a core problem: how to have a good ground plane.

And then my club president mentioned the antenna he uses: the Diamond NR770HB. This is a folding antenna that is quite tall on the vehicle. My concern about a ground plane was made moot because on 2 meters, the antenna is a half-wave in length. For 70 centimeters, the antenna acts as two 5/8-wave lengths. In other words, I could forgo my worry about a ground plane if I used an antenna like this.

Mounting the antenna

Still, I had no good place to mount it. Eventually, I opted to try the Diamond HRKS Adhesive-Backed Mount. I placed this on the driver’s side near the rear of the cab. To this, I mounted the Diamond NR770HB antenna and routed the skinny coax (RG-316) down the seam between the cab and the truck bed. I brought the cable inside the plastic kick plate below the rear door and then up into the cab, temporarily securing it with a bit of tape.

That worked pretty well. I drove through several heavy rains without any water leaking into the interior of the cab. The antenna has been a joy to operate with. It has more gain than my old mag-mount and it is very stiff. That rigidity translates to less “picket fencing” when I’m driving and transmitting.

Then came the night when I got an important phone call from my boss while I was driving. It was coming on to dark so I pulled into a fire station parking lot to complete the call. It was windy and there was plenty of road noise from a nearby highway, so I didn’t really notice that in the dark, I had backed the antenna right into a stout tree branch.

The next day, I glanced up at the antenna and saw it was leaning over at about 45 degrees. The adhesive mount which had survived rain and snow and +70 MPH speeds without complaint had been partly lifted off the cab roof by the stress applied to the antenna when I backed under the branch.

Mounting the antenna the second time

Back to the drawing board. I rejected the idea of replacing the HRKS mount (although I reserve the right to go back to it at some point). Instead, I bought a much less costly mount, the Comet RS-660U roof rack mount.

The RS-660U isn’t difficult to mount on a roof rack crossbar except for one thing: once you loosen all of the Allen screws, the mount seems like an amoeba in your hand. It felt like it was moving in every possible plane all at the same time while I was trying to manipulate it into position. When I eventually got it where I wanted it, I grabbed my trusty roll of blue tape and gave it a quick couple of wraps to hold the pieces in position. That made it easier to get all of the screws tightened without the pieces moving around too much.

Once secured, I went to move the UHF mount from the HRKS to the RS-660U and found that I had not allowed sufficient slack in the RG-316 cable. I had secured the cable to the vehicle with small strips of Alien Tape, making it easy to remove the cable. I also removed the tape and this time around, used strips of Gorilla Tough & Clear Mounting Tape to secure the cable. This tape is purported to be usable as a permanent indoor-outdoor tape.

So far, this solution is working well. I’ll need to carry a bit of duct tape (or a similar product) to hold some of the slack coax at the RS-660U mount when I go through a car wash. This isn’t much of an imposition since I need to remove the antenna when I take the truck through the wash. I have not yet tested the Gorilla mounting tape in a car wash. Note that I also use a screw-on cap for the UHF mount so that I can keep water out of the fitting when in car wash mode.

Interestingly, when I used the adhesive mount, I could pass under 9-foot-tall openings for drive-throughs. With the antenna mounted a few inches taller on the crossbar, the antenna strikes those same 9-foot-tall canopies over drive-throughs.

Will try a shorter antenna

To make going through such establishments a little easier, I’m going to try a Comet SS-680SB Mobile Antenna. This 2m/70cm is about a foot shorter than the NR770HB. Like the NR770HB, it is a half-wave antenna on 2 meters and two 5/8-wave sections for 70 centimeters. It will arrive next week. I expect that I’ll use it most of the time and reserve the taller NR770HB for long cross-state trips where the additional gain will come in handy.

I have to say I am really impressed with the Diamond NR770HB antenna. People have been reporting that my transmissions are clearer (and they were already pretty good through my Kenwood TM-D710G radio). I notice that reception is also clearer, perhaps because of the gain, but probably because it’s a stiff antenna that doesn’t wiggle around much at highway speeds.