----- Original Message -----
From: "RCARIELLO" <RCARIELLO@si.rr.com>
To: "Towertalk" <Towertalk@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
> 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
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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