Suction Mount Antenna

SCARS members perform a number of emergency communications projects that require radios to be mounted in or on vehicles. With more vehicles going to aluminum or fiberglass panels, the magnetic mount antennas aren’t able to do the job. Mark Kleine N5HZR has come up with a suction cup mount that will connect to a flat surface, or a curved car window, or a vertical pipe, or hang from a tree, or balcony.

The suction cup mounts say they are rated for 125 pounds each, and they have stayed put in wind, rain, heat, tree strikes, vibration, and some high-speed runs. We have no idea how much power these will take, but we’ve used them on 25-watt radios without any trouble. These mounts can be built quickly and inexpensively from locally sourced parts. The most recent build cost about $32 for each antenna. The wind noise is very minimal, and you probably won’t notice that it’s there.

Parts List

The following parts are needed to make this project. These can be purchased from a number of sources, however, the Internet sources listed here should give you all of the details you need to source them somewhere else.

Construction

First, cut the PVC pipe to the lengths shown above. Glue the pieces as shown in this photo. Make sure the two 7″ pieces are parallel and are pointing in the correct direction.

Second, prepare the coax, by cutting the 50′ cable in half. Each 50′ cable makes wires for two antennas. Make sure you poke the cut end of the coax into the bottom 7″ PVC pipe until it sticks out the top before you put the antenna together. Your antenna won’t make that sharp bend.

Third, prepare the end of the coax by slicing off 2″ of the outer insulation and twisting the braid into a wire. Then trim off 1/2″ of the center insulation and twist the inner wire tight.

Fourth, strip 1/2″ insulation from one end of each of the 19 3/4″ wires. Wrap the center coax wire around one of the wires and wrap the braid around the second 19 3/4″ stripped wire, as shown here:

Measure out from the center to each end of the wire to the proper length for your transmitting frequency. We trimmed each direction to 19 3/4″ long.

Finally, wrap some tape, or shrink wrap around the center of the dipole, and stick the braid wire down into the tube. Pull the coax until the top of the center conductor wire is flush with the top of the PVC pipe. Place a cap on the top of the 3/4″ pipe and either tape or seal the bottom with silicone so the coax stays in place.

Final Assembly

Place the two suction cup dent pullers on your window, or flat surface, about 13″ apart. The handles should be place horizontally so you can attach the 7″ PVC pipe to them with the hose clamps. Arrange the pipes so the antenna is as close to vertical as possible. Then tighten the hose clamps.

Drape the coax into the car into the least used door frame, taking care not to crimp the coax in the door seal. Route the cable through the vehicle to your radio.

Alternative Antennas

This project was initially built as a 19″ dipole antenna. The was a first attempt to get these up and running quickly. Testing the 19″ antenna put the SWR at 2.4:1 at 147.66 MHz. There was a nice wide flat 1.5:1 area up at 153 MHz. So, 19 3/4″ looks like a better length for the top of the ham band. We’ll lengthen the dipole and test again.

Future expansions include removing the simple dipole and making a Slim Jim J antenna or a standard J antenna. Hopefully, these will test out for VHF and UHF dual band usage. More details on this modification as time permits.

Alternative Mounts

If you need to use this antenna in an area without glass or a similar flat surface, you can drill a hole in the top cap. Run a string through the hole and you can hang this from a tree, or a balcony for emergency use.

You can also use the hose clamps to connect the pipe to an existing vertical pipe, or railing.