Fred C. Judd, G2BCX, described his J Type Integrated Matching stub antenna in Practical Wireless, April 1978. A 28MHz version was described in November, 1980, and a 432MHz version in March, 1983. The Slim Jim, as it became known, was made by many amateurs worldwide and is an omnidirectional free space antenna with a claimed radiation efficiency 50% greater than a ground plane. It is an end fed, vertically operated, folded dipole. Mine was made around 1979 for mobile use with an IC-22A. As the antenna is ground independent, you can really mount it anywhere on a vehicle.
My particular 2m antenna is designed to be quickly attached or removed and connects with a bracket bolted under the vehicle. I consider it an excellent performer and is stable to well over 100km per hour. The Slim Jim has a low angle of radiation and, unlike a normal vertical whip, remains vertical at speed which probably enhances its performance.
No antenna construction information is provided here. I could probably provide a copy of the magazine article if you cannot locate the information anywhere else.
Vehicle Mounting Bracket - The thumbnail at left shows the mounting bracket that was bolted under my 1984 Nissan 300C. A flat plate was bolted against the chassis with a length of approx. 19mm square steel tube on which to slide the antenna mounting foot.
Antenna Mounting Foot - The thumbnail at left shows the mounting foot that slides onto the bracket shown above. The foot is made from approx. 25mm square steel and is an easy slide over the vehicle mounting bracket. Two bolts secure the mounting foot.
2m Mobile Slim Jim - The thumbnail at left shows the complete antenna. It is secured to the mounting bracket on the vehicle with two bolts. Easy to put on, Easy to take off. It takes about two minutes.
Partial Mounted View - The thumbnail at left shows the mounted antenna. The coax cable enters the boot for connection to the coax coming from the rig.
Complete Mounted View - The thumbnail at left shows the complete mounted antenna.
Ever wondered how you were going to mount a rig in a modern vehicle? Here's how I did it.
IC-290A Front View - The thumbnail at left shows a front view the transceiver mounted on an angled bracket fixed to a horizontal plate sitting on the transmission hump behind the front seats and secured with two screws under the rear seat. The transceiver faces forward and is easily operated and is not in the way. I don't really think that obscuring the rear cigarette lighter and rear car radio volume control being in the way. No problem even with three rear passengers.
Side View - Here is another view taken from the rear seat and the side of the mount.
Created 2005 by
Kevin Crockett. Comments and suggestions may be e-mailed to