Re: [Discuss-gnuradio] Looking for more antenna details

[Eric Blossom]

On Fri, Sep 08, 2006 at 11:41:22AM -0600, Jim Borynec wrote:
> Hi
> 
> I was looking at the picture:
> http://comsec.com/2x2-antenna.jpg
> and trying to replicate it (or something much like it).

Here's a closeup:  http://comsec.com/2x2-antenna-closeup.jpg

> In the center of the ground plane, there appears to be a metal plate
> of some sort.

It's actually particle board covered with metal furnace tape.  Turns
out that the adhesive on the tape is a pretty good insulator, so it
didn't work out that well.  Just wrapping the board with aluminum foil
would probably work, or just use a piece of sheet metal.  You want
something that's conductive and rigid and can be connected to the
hardware cloth.  I used 1/4 inch square h/w cloth.  I'd probably
go for the 1/2 inch square stuff next time.  It's stiffer.

The PCV pipe is 1 inch schedule 40.  You can stiffen the joints up by
slipping wooden dowels in place, then drilling a hole through the pipe
+ dowel for a bolt that will keep the dowel from drifting around.

> The anntenna appears to be attached to the plate via
> some sort of cylinder.  what is that?  does it contain a coil?

It's an SO-239 connector (Radio Shack).  No coil or anything, it's
just there to serve as a socket for the antenna wire. 

> What is the relationship of the plate to the antenna feed wire?

The plate's connected to the shield on the coax.

> how do you attach the ground plane to the cable without breaking the 
> conection every time you more the assembly?

The cable is soldered to the back of the SO-239 connector.  The shield
is effectively connected to the ground plane.  There's no quick
disconnect, though you could build one.  I just coil the coax up and
use zip ties to hold it to the screen while moving it.

Eric