Tower Trailer – Still a Mobile Station?

You may recall that I experienced a functional failure of my roof rack due to the extra leverage applied by its roof-mounted antenna tower. Read here for more info. Note that nearly any factory-installed roof rack is up to this task since they’re mounted with more hardware and attach to structural points along the vehicle’s roof. Having an aftermarket rack that attaches to a “naked roof,” I determined that there is no way to strengthen the rack in my particular application. Rather than abandon the idea of using a mobile tower for contesting, I opted to move the complete tower setup to my small utility trailer. It presents its own challenges, but also a few benefits. Here’s how I made the switch.

I didn’t purchase a trailer just for the radio tower. I’ve been pulling small utility trailers with my VWs for over 25 years and have had my baby trailer since 2015. It’s already had two different racks mounted. As a result, there is a series of holes drilled into the top rail at 28-inch and 32-inch intervals. Everything shown in this drawing easily transferred directly from my car’s rooftop to the trailer, including the Yakima JetStream crossbars. I reduced the JetStream’s crossbar spread from 32 inches to 28 inches so that I could keep my existing Yakima Outdoorsman 300 truck rack.

I mounted the JetStream crossbars directly to the trailer’s top rail using T-bolts, the idea being to eliminate the weak point of crossbar towers. Yes, that could reveal a new weak point. If a crossbar point fails, then it will be intuitive and fast to switch to a strong Unistrut replacement since I already have Unistrut elsewhere in the setup. The only pitfall to having my crossbars mounted directly to the trailer is that clearance beneath them is only 15 inches, which may limit my cargo options. These days, I use my trailer mostly for storing discarded cardboard and eventually taking it to a collection site. It’s also great for taking HAZMAT to the same site. It’s easy to remove the JetStream crossbars, should I need to transport a larger cargo. It’s fastened by only four nuts!

I mounted my Outdoorsman 300 truck rack years ago so that I could create a “double-decker” for use when supporting bicycling events. Of course, the small size of my trailer means that heavier cargo rides in the trailer (there’s 75 gallons of water beneath the ice chests in this photo), with lighter cargo riding on the topside basket. The cargo basket is easy to remove/install when I’m ready to mount the tower. To be honest, the cargo basket can be a bit of a head-knocker; so, I don’t mount it unless I have a specific need for it. 😀

The tower itself is bolted to the JetStream crossbars exactly as it was on the car (see image below). The only exceptions are the 28-inch crossbar spacing, a wider side-to-side spread, and the omission of a third Unistrut bar that supported a hinge setup. I can easily access the tower and even the top antenna with a step that I built into the trailer’s tongue (see photo below). So, I don’t need to tip the tower as I did when it was on top of the car. Also, instead of guy lines, I used a pair of DXE heavy duty saddle clamps to attach the leading tower legs to the front crossbar of the truck rack (pictured here). The result is far more stable than what I had accomplished with Ultra-Cord guy lines.

It would seem intuitive to carry only what’s necessary during a radio contest. However, it’s also important to carry ballast low in the trailer so that the tall tower doesn’t tip the trailer in turns or crosswinds. I considered options, but quickly settled on filling a 25-gallon storage tote with 300 lbs of sand. The ballast is compact and easy to position for a balance between suspension preload and proper tongue bias. I can even mount my spare tires to the back of the trailer and position the 300-lb ballast to compensate for their rearward weight. The wood decking boards added nearly 100 lbs of additional weight to the bottom of the trailer.

My initial road test went very well… until it didn’t. The extra 400 lbs in the trailer vastly improved its ride. However, one of the antennas suffered a mechanical failure. I had purchased my “Rover Special” Yagis with optional quick-release (QR) flanges since I thought that I would disassemble the tower between each outing. Instead, it has remained assembled and stored in my back yard in a stand that I made from concrete and a bucket. I left the QR parts in service, thinking that they might be useful someday. Little did I realize that they are a weak point that’s been waiting to surface for quite some time. A tiny pin was all that kept each Yagi from being able to rotate and fall off. One of mine broke on my first road test with the trailer.

This video shows how much movement that the QR configuration allowed, which was exasperated by the tower riding on a trailer and in the turbulence behind the car. The pin on the other Yagi had failed, too, but hadn’t fallen out yet. Rust on the broken end indicates that the failure had happened long before the tower had ever moved to the trailer. So, this casualty was going to happen at some point regardless of where the tower was riding. I removed all QR components and tapped the flanges to accept ¼” screws, which is the same size as the saddle clamps. This photo shows the difference between the two mounting configurations. The QR function is removed, but all movement between the boom and mast is also gone. Best yet, should I need to remove an antenna, I can remount it exactly where it was without having to realign anything.

How does this setup differ in overall height when compared against the tower being on top of the car? The JetStream crossbars are now 28 inches lower than before. That reduces the height of the 6m Moxon from 11’8″ to 9’4″. That’s better for tree limb avoidance, but perhaps a little worse for signal propagation. I may explore a telescoping mast since the top of the tower is easier to reach than before. But that’s not an immediate goal. For now, I want to explore the feasibility of driving with an erected tower on such a small trailer. Mounting the tower on the truck rack would restore the lost height. However, I prefer the stability that’s afforded by mounting it lower.

I mentioned improved tree limb avoidance as a likely benefit to having my setup on a trailer. I think rapid deployment is another. Previously, when I prepared for a contest or exhibition trip, I’d spend a few hours building everything on top of the car a day or more before the drive. Then, I’d have to drive with that configuration until after I was done with the trip and could remove it. The challenges behind that depended on the weather. If rain, sweltering heat, or frigid weather was forecast, then I’d either have to setup/remove during a wider weather window or just deal with the challenge. With the trailer, I can set up far in advance and then take just a few minutes to couple the trailer and connect the cabling. Disconnecting afterwards is even faster. Then, the trailer can sit for as long as I want before deciding to remove the equipment, if I even bother with it. Perhaps it’s too enabling for a lazy operator! HAHA!

Another benefit to having my tower on a trailer is the newfound separation between the Yagis and the loops. With everything on the roof, it’s nearly impossible to get it to work without some sort of interference between the elements, both electrical and mechanical. The Yagis collide with the ATAS-120A whip, the 432 MHz Yagi detunes the 6m loop, the tower itself detunes the 6m loop unless I offset it toward the passenger side of the roof, and the Scorpion cannot tune 80m if the Yagis are mounted. But when do I really mount everything at once?

Remember: Everything on the roof was my exhibition setup! In reality, I don’t mount HF antennas during VHF contests; and the asymmetry of mounting the tower toward the passenger side of the car was a very short-term problem. Regardless, the large area of separation that the trailer provides solved all of these problems, with the exception of mounting the Scorpion. Again, I don’t use the Scorpion during VHF contests; so, that’s only an exhibition challenge. I have a solution to that. See my exhibition at select hamfests in 2024 to learn more.

The coaxial feed lines and rotator control cable are not yet sorted. I can operate while the vehicle is parked since I have the pass-thru ports on my rear window, especially if I park in a jackknife as shown in the photo album below. But my ultimate goal is to be able to operate on the move. I’m going to see if I have more grommets available in the trunk floor so that I can run coax to the trailer from under the bumper. Being able to move with everything connected would provide the kind of flexibility that’s very useful in emergencies or if I’m operating on a rainy day. Besides, it’s not a “mobile station” unless it can operate on the move! 😀 See the ARRL’s Mobile DXCC Award rules for details. It’s the ONLY place where I’ve seen a “mobile station” defined by a recognized authority.

My next VHF contest is not until January. So, I have plenty of time to plan and finish the project. Overall, I think this setup provides good separation between the loops and the Yagis without adding too much additional feed line. While a taller tower may be better, I hope to achieve most of my antenna height by driving to higher elevations. What do you think? Am I nuts?

Micro-Tower 2.0,


About Scott

I grew up near Houston, TX and served in the U. S. Coast Guard ordnance and electronics communities for over 35 years. I became involved with ham radio and computers in 1995. The explosion of technology made my jobs and hobbies quite interesting. My hobbies include Volkswagens, bicycling, photography/videography, electronics, ham radio, and web management.
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One Response to Tower Trailer – Still a Mobile Station?

  1. Pingback: June 2023 ARRL VHF Contest | KE4WMF

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