Extension Mechanism

[Al Skierkiewicz]

Originally Posted by acer_7

Hey guys,
Does anyone one knows how does the car antenna extend (from the mechanical and electrical sides)?

As shown in the picture above, many have a plastic rack gear driven by a pinion on the shaft of a motor. The drawback it that for extension, the rack must slide up inside the telescoping tubing sections without binding. Since the tubing is thin wall, there is not a lot of dimensional change between the inside tube and the outside tube. (about three or four telescoping sections maximum) The sections are designed in such a way that the inner one has a larger outside diameter at the bottom of the tube than the inside diameter of the next larger tube. As the inner tube extends, it "grabs" the outer tube and so forth for all of tubes.
There is a fishing pole available through several outlets here in the US (Cabellas and Gander Mountain). It is called a breem pole or sunfish pole. It is made of fiberglass and graphite composite. It starts a little less than 2 meters long and extends for almost 7 meters. It is very lightweight. Many ham radio operators here use this pole for portable antennas. The design is a friction fit between pole sections and it operates much like the power antenna above. Cost in US about $20 plus shipping.
An antenna article here uses such a pole. http://members.aol.com/realhamradio2/W2IK-ANTENNA.html

[acer_7]

Thx a lot . . got it