HiQ Antenna Mount

HiQ 4/80 RT Antenna Truck Mount

I considered a lot of different mounting positions for my new Hi-Q 4/80 RT antenna. I finally settled on the position you see on the photo to the right. After deciding on a position, I had to design and build an antenna mount.

My main goal for the design was strength and rigidity without compromising the basic look-and-feel or usefulness of the truck. Also, I wanted a design that did not require too much from the truck body itself -- that is, no big customized changes or holes and so on. Also, I wanted a design where I could easily make use of the quick disconnect and have a place to put a shunt coil.

Finally, I wanted a design that I could build using materials that I could cut, bend, mold, and fashion into a mount myself in my shop. I consider this work an experiment and not necessarily the final solution. I already have some ideas on improvements and I am thinking of a version of this antenna made from steel but I would need someone else to do that work as my shop is excellent for woodworking and just passable for aluminum but not outfitted at all for working in steel.

Close-up of Truck Mount

Here is a close-up of the antenna truck mount. The PVC plastic box on the top portion covers the shunt coil and it is attached to the aluminum channel stock with four 1/4 inch machine screws into a tapped holes.

The transmission coax and the 4-wire cable for antenna motor and read switch turns counter come up through the floor of the truck bed and protected by one-inch cable wrap. This cable assembly snakes through the under-carriage and then up into the rear crew cab through the floor. This assembly reuses the same implementation I used for my previous whip antenna.

I have an SO-239 UHF socket attached to the aluminum channel to allow me to disconnect the antenna for maintenance or testing or whatever. The backside of the SO-239 is packed with COAX seal.

Close-up Top View

In this view you can see how the aluminum channel stock and angle bracket is attached to the truck. I use four holes that I have access to through the stake hole. The aluminum bracket in the stake hole gives strength to the truck sheet metal. The bottom of the channel stock is also attached through the bed of the truck to a similar small metal plate underneath to provide strength. Without these metal backplates the bolts could eventually move and twist or bend the sheet metal.

There is a ground strap attached to the lower bolts of the upper part of the mount and also to the lower attachment underneath the truck. There are a number of ground straps tieing the truck bed and frame and side panels together.

This assembly is absolutely rigid and does not move, does not flex, and does not put very much stress on the sheet metal of the truck.

The Starting Point: Raw Materials

Here you see the main parts of this antenna mount. The aluminum channel stock and the aluminum angle stock. Both are 1/4 inch thick. The angle stock is 2 1/2 by 3 1/2 inches and the channel stock is 2 by 3 1/2 inches. In this photo, I have already cut the stock to length and drilled the main holes in the angle stock. The large hole is for the antenna disconnect bolt.

Although these are sitting on my cabinet saw, I did not cut them with my carbide tip blade that only sees wood, not aluminum. I cut both pieces to size using a regular hacksaw, by hand. After cutting with the hacksaw, I used my belt/disc sander to grind the pieces to square and remove any burr or roughness.

By the way, aluminum stock is cheap when you buy it the right way. I pay by the pound no matter what shape it comes in. Aluminum has gone up a bit since my last project. I had to pay $2 per pound and the stock I have here is about 5 lbs total. I buy from Seattle Iron Works located in Seattle, Washington.

Initial Layout

Here is the channel and angle stock in position. It is bolted in on the top but this setup is just temporary and only for doing adjustments and other measurements. One task is to make sure that the mount is aligned correctly so that the antenna will stand up straight and true.

In this photo I have not yet made the bracket that fits on the bottom of the channel stock and used to bolt the assembly to the truck bed. Unfortunately I do not have a picture of this but I used 1 inch by 1 inch angle stock that was cut to fit between the channel sides. I also rounded the edges to fit the inside radius of the channel stock.

Initial Layout: Top Closeup View

This photo shows the closeup of how the angle stock and channel stock mate together for the main antenna mounting bracket. As you can see, I had to round over the inside edge of the channel stock due to the rounded inside radius on the angle stock. I did not measure anything but just eye-balled the roundover on my belt/disc sander.

Initial Layout: Bottom Closeup View

This photo shows the bottom bracket in place. I have not yet drilled the hole to accept the bolt that goes through the bottom of the truck bed.

Adjustments and Alignment

This picture shows the setup for doing the alignment adjustments making sure that the antenna is in a straight vertical plane from all directions. Here you see how I used shims to space out the channel stock away from the side of the truck. This was a slow process because I had no helpers. Another hand would have been great to hold things steady while I made adjustments.

After finalizing the position I then determined the exact position to put the hole through the bottom bracket through the truck bed. Also, I made a little spacer from a piece of ironwood that sits behind the bottom between the channel stock and the side of the truck. Ironwood is pretty heavy and dense wood that will last forever without any special treatment. I just happened to have some available.

Close-up View of Antenna Disconnect

This is a closeup that shows how the HiQ antenna disconnect fastens to the angle bracket. Not much more to say here.

Antenna Shunt Coil and Tuning

This picture shows my first shunt coil where I am doing the initial tuning and adjustments using my MFJ-259 antenna analyzer. I jury-rigged a temporary switch using the DPDT toggle that came with the antenna and a little 12 volt power source. I would move the antenna until a dip on the SWR and then do fine tuning. After final position with the antenna analyzer, I would double check using my Icom 706 and an external SWR meter.

This particular coil is rather large. It is 2 inches inside diameter and about 2 inches long. You can count the number of turns in the photo. This is #8 copper wire -- very rigid and holds the coil form and shape very nicely.

I am now on my third coil. I wasn't happy with the final R,X values for my favorite 80 meter frequencies so I made a second coil. That worked well but for some reason when I used my N2VZ Turbo Tuner with it, it could not find resonance on 80 meters. So, a third coil. Now, everything works just fine.

PVC Plastic Cover Box

I made a box out of PVC sheet plastic that is 1/4 inch thick. I bought the plastic from Tap Plastics scrap bin at $1.50 per pound. I think I have about 2 lbs. I cut the plastic to size using my cabinet saw with an old carbide tip blade. Then, I used one of my hand planes to create a glass smooth finish surface on all the edges. I glued the box together with regular PVC glue -- just like the stuff you use with PVC pipe.

Four holes, two on each side, allow 1/4 inch machine screws to fasten this into the channel stock into tapped holes. Aluminum if really easy to tap. The box is closed on the top but open on the bottom. This box is a lot stronger than I thought it would be.

Top View of Cover Box

This photo shows a close-up of the top of the cover box. This is not water tight as there is a slight razor thin gap where the plastic and the aluminum mate. However, being water tight was not a goal.

Painted Black

I painted the aluminum black using flat black primer sold in car parts type stores. The flat black matches the inside lining of my truck bed better then something shiny.

HiQ Antenna Truck Mount