[TowerTalk] HELP Coax Phase Line Shield Switching

[Jim Lux]

----- Original Message -----
From: "RCARIELLO" <RCARIELLO at si.rr.com>
To: "Towertalk" <Towertalk at contesting.com>
Sent: Tuesday, February 17, 2004 5:31 AM
Subject: [TowerTalk] HELP Coax Phase Line Shield Switching


> COAX PHASE LINE SHIELD SWITCHING
>
> Hello to all,
> I am in the process of constructing a two element phased vertical system
for
> forty meters. I would like to be able to switch the antenna pattern
> direction remotely from inside the station.
>
> At first glance the information given in the antenna books seems simple
> enough. A single-pole double-throw relay to the center conductors of the
> Coax lines at a junction box and I am all set.
>
> Taking a second look it seems to me that the Coax shields should also be
> switched the same way. This would require mounting the Coax fittings
> (SO-239) on a plastic box connecting the shield side of the Coax fittings
> through a second single-pole double-throw relay.

Exactly... you need to be able to switch both shield and center conductor.

>
> I will be using Jennings RJ1A vacuum relays for the switching.
>
> I am shore there will be some degrade in the overall system performance as
 compared to a fixed direction system with no pattern direction switching.

Can't see why there would be degradation in performance... You're persumably
doing a Christman type phasing, so the match should be fairly good.
Assuming the elements are a reasonable distance apart (i.e. not 1/16
wavelength or something), then the reactive current between the elements
will be small, so coax losses should be small.  The loss through the relay
is negligible.