[Antennas] Expanding foam and antenna tunning

[Dave Kelley]

At 04:01 AM 8/26/2002 -0400, you wrote:
>Hi All,
>
>I constructed and installed a 50 Mc vertical coaxial center fed
>antenna this past weekend, the antenna itself is housed inside
>a fiberglass fishing rod in order to keep the coaxial vertical.
>the antenna tunned nicelly throughout the band with less than 1.7
>SWR.
>The fishing rod itself seems to handle the wind nicely but the base 
>of it where it is secured on two wooden planks with U bolts may need 
>some reenforcing so it doesn't crush from the wind pressure at the U 
>bolt contact points.
>
>I thought of the Expanding Foam (Poly something....) used for 
>insolation, but I was thinking, would this effect tunning ? has 
>anyone had any experience with expaning foam on antenna applications ?


The expanding foam might crush as well.  I would suggest using
something more solid, like solid PVC or plexiglas (Perspex).  The
effect on tuning should be minimal if the material you use is not
too lossy.  Most solid plastics should work okay.

73,
Dave NB4J


--
Dave Kelley, NB4J
Lewisburg, PA
Union County
nb4j@arrl.net