I am a big fan of vertical antennas – especially for POTA activations. Recently, I decided to deploy “Tennessee Walt’s” world-famous EFHW TennTenna (Search Ebay for ‘TennTenna’) on 20M.
The antenna driven element for 20M is about 33′, trimmed to the lowest SWR. This requires a 10M mast to get the wire fully extended.
I own two 10M fiberglass telescoping antenna masts. One from TN07 , and the other from DX Commander in the UK. The TN07 is super heavy-duty and virtually indestructable. The DX Commander is lighter, thinner, but also quite rugged.
One drawback of the TN07 is its use of large rubber caps on each end. The diameter of the caps are 5.5cm (2.2″). This means when the bottom cap is in place, the mast will not fit into a 2″ pipe. The DX Commander uses a threaded cap on the bottom, which does not increase the overall diameter of the mast. It fits into a 2″ pipe.
When I went looking for a “drive-on” flagpole mount to hold my masts, I was surprised at how flimsy most of them are. They were also too short (length-wise), most being about 15″. This puts the mast dangerously close to the vehicle, which can cause problems in high-wind conditions.
So, I set out to build my own.
I wanted something nearly indestructable, yet easy to transport. It also needed to fit both my masts.
When I was done hacking, this was the result.
Here is the parts list:
1 – 2′ x 4′ sheet of 3/4″ pressure treated exterior plywood
1 – Can Rustoleum exterior paint spray paint
2 – 12 x 24″ aluminum tread plate sheet metal
1 – Outdoor deck mounted umbrella base
1 – 5/16″ Fluted threaded knob
1 – 5/16-18 Threaded T-Nut
4 – 3/8 x 1- 1/2″ exterior carriage bolts
4 – 3/8″ flat washers
4 – 3/8″ nylon insert lock nuts
1 – tube construction adhesive
Assembly steps:
1) Collect the required parts from the above list.
NOTE: To save time, have the big-box store cut the 2′ x 4′ plywood to 12″ x 24″ at the store.
2) Lightly sand both sided of the plywood to ensure both sides are smooth. Remove any sanding residue with compressed air or a tack cloth.
3) Paint all surfaces of the plywood with the Rustoleum spray paint. Be sure to apply mutliple coats of paint to ensure good coverage. Let dry overnight.
4) Align the umbrella stand on the plywood where you want it, then mark the bolt holes on the plywood with a permanent marker. Cut four – 3/8″ bolt holes at the marks through the plywood.
5) Line up the metal plates with the plywood and drill holes in the metal using the plywood holes as a guide. Place a metal plate on a piece of scrap wood. Align the plywood to the plate, and drill the holes into the metal. Repeat for the second plate.
6) Apply constuction adhesive to one side of the plywood. Spead it in a thin layer across the entire surface using a putty knife. Line up one of the metal plates with the shiny side up, and the bolt holes lined up.
7) Flip the assemply over, and repeat Step-6 on the other side.
8) Insert the four carriage bolts through the bottom side plate holes. Place the umbrella base on the bolts on the top side and tighten the base to the plate with the washers and lock nuts.
9) Use your truck or car as a clamp. Drive a tire onto the end opposite the umbrella brace. Leave it in place until the adhesive has fully cured. I let my truck sit on the assembly overnight.
10) Determine where on the pipe you want to place the threaded knob that will secure the mast in pipe. Mark it with a permanent marker. Drill a 5/16″ hole into the pipe. Be careful not to drill through the other side of the pipe.
11) Remove the prongs from the threaded T-nut with a pliers. Then bend the 3 flat parts of the T-nut backwards to fit flush to the interior contour of the umbrella stand pipe. Place the T-nut in the hole you drilled in Step-10 from the inside of the pipe.
12) Glue the T-Nut in place using a heavy duty expoxy or something similar. I used JB-Weld epoxy for this. Screw the threaded rod into the T-Nut from the outside of the pipe. I used a piece of 1-1/2″ PVC pipe on the inside of the pipe to act as a clamp to secure the T-Nut. Screw the threaded rod into the pipe until it strikes the PVC pipe. Tighten it securely. This will clamp the T-Nut against the pipe while the epoxy sets.
Your drive-on mast support is now ready for service. I applied some silicon lubricant to the threads of the pipe.
The mount base without the pipe attached weighs 11.4 pounds (5 kg).
This support should last for years. I have used is several time for my POTA activations. I drive into the park. Back in to a parking space. Drop the mast mount behind the drivers tire, and roll the tire up on the mount. Next, I screw in the pipe and I am ready to deply the mast of choice for the day.
N1SPW