[TowerTalk] CATV Hardline As Elements

[Jim Lux]

At 10:24 AM 9/2/2004 -0400, N4CW at aol.com wrote:
>Being financially "challenged" and not having any reasonable sources of
>aluminum for antenna experimenting, I thought of using CATV hardline as 
>elements
>(on perhaps a 6- or 10-meter yagi). I've got some 7/8" that I can use. It's
>fairly rigid in short lengths.
>Has this been tried before? Successfully?
>If not, what are some potential problems? I just plan to ignore the center
>conductor in the parasitic elements (but, I have thought of feeding the 
>center
>conductor in the driven element and allowing capacitive coupling to the
>aluminum outer shield to transfer the r.f. with little loss.)
>Thoughts and advice are appreciated.
>Bert, N4CW/1

Another fairly inexpensive way to improvise elements is to use multiple 
copper wires on the surface of a cheap substrate (PVC pipe, wood, etc.) 
It's an easy way to get a "fat" element which has other useful properties 
(e.g. bandwidth).  For a 10m antenna you're looking at elements which need 
to be about 8 ft long (sticking out from the center).

Also, consider the idea of using truss and guy type construction to work 
with floppy lightweight tubing (like "Schedule A" thin wall PVC).  Kind of 
draggy from a aerodynamic standpoint, and not particularly durable, what 
with UV, etc., but great as a support for experimenting.  You build the 
mechanical structure once, and then just zip-tie wires to the struts.

You might also be able to use that aluminum tape used for HVAC ducts on the 
surface of something as a element. It's fairly inexpensive (50 yd, 2" wide, 
runs about $10) and is around 3 mils thick.  Heck, aluminum foil and glue 
might work.  Skin depth is pretty small at 30 MHz (about 0.0006" in 
Aluminum), and most household aluminum foil is in the area of 0.001" 
thick.  The rule of thumb is that if your layer is 5 skindepths thick, then 
you've got more than 99% of the conductivity of a solid bar.  2 skin depths 
is 86%

(check out the on-line skin depth calculator at: 
http://www.microwaves101.com/encyclopedia/calsdepth.cfm

very handy)

Jim, W6RMK