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 came 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. These antennas are rated for 75 watts, and we’ve used them on 50-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.
After thousands of miles of operation, we’ve made some adjustments to the design and they seem to work even better. This year Lea Greenleaf W5HLG updated the antenna to an Ed Fong J-antenna design and shortened the horizontal stubs to allow the suction latches to operate fully. These adjustments provide about 3.5 dB of additional gain and make for easier installation on the vehicle.
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.
- Ten-foot long pipe (makes two antennas) – 3/4″ PVC class 200 pipe – Cut into four pieces, one 40″ long, one 12″ long, two 4″ long – Home Depot – $1.81
- One 3/4″ PVC Tee – Home Depot – $.29
- One 3/4″ PVC Elbow – Home Depot – $.64
- Two Suction Cup Dent Pullers – Harbor Freight – $15.00 (These are typically on sale for $7.99)
- Four 2 3/4″ stainless steel hose clamps – Home Depot – $5.16
- 25′ RG 8x Coax with PL-259 connector – eBay – $20.00 for 2 (50′ cable, cut in half)
- 300-ohm twin-lead for Ed Fong antenna, 174a coax, and some shrinkwrap tubing
Construction
First, cut the class 200 (irrigation) PVC pipe to the lengths shown above. Glue the pieces as shown in this photo. Make sure the two 4″ pieces are parallel
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 4″ PVC pipe until it sticks out the top before you put the antenna together.
Third, build the J-antenna according to the Ed Fong article in a 2003 QST.
The roll-up version of this antenna (to be used without a class 200 pvc pipe) is available from a 2007 QST article by clicking here.
Final Assembly
Place the two suction cup dent pullers on your window, or flat surface, about 13″ apart. The handles should be placed horizontally so you can attach the 4″ 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. Our recent experiences have encouraged us to mount these on the driver’s side of the vehicle. An abundance of low hanging branches kept striking the passenger side devices. Route the cable through the vehicle to your radio and take off.
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.