[Antennas] Unused resonant antennas - shorted to ground or floating?

[Jim Miller KG0KP]

I can do that (use inductors across the feed point to the radial field(and 
ground them at the station)) and what I had in mind was a pair of phased 
verticals (actually Butternuts) and looking at 90 degree separation on 80 
but also realizing I will probably be better off with an omni pattern on 
bands above 40 (20 maybe) so wanting a way to inimize the effect of the 
unused vertical.  Still have to try modeling it but I am in kindergarten on 
modeling.

Thanks guys, de Jim KG0KP

----- Original Message ----- 
From: "Chris Boone" <cboone at earthlink.net>
To: "'Antennas Reflector'" <antennas at mailman.qth.net>
Sent: Thursday, December 24, 2009 10:18 PM
Subject: Re: [Antennas] Unused resonant antennas - shorted to groundor 
floating?


> AM broadcast stations usually ground elements in a Directional Array that
> are switched out (when either omni or another directional pattern is used)
> and I have seen inductance in series with the ground in a lot of 
> instances.
>
> As for emergency operations in broadcast use, most AM do not have a backup
> tower.
>
> They can apply for a Special Temporary Authorization (STA) with an 
> emergency
> antenna of any length with a radiation efficiency less than it's main
> antenna (and only 25% of daytime power is allowed under STA use).
>
> Chris
> WB5ITT
> SBE 134 frequency coordinator
>
> -----Original Message-----
> From: antennas-bounces at mailman.qth.net
> [mailto:antennas-bounces at mailman.qth.net] On Behalf Of C.Whitaker
> Sent: Thursday, December 24, 2009 9:24 PM
> To: Antennas Reflector
> Subject: Re: [Antennas] Unused resonant antennas - shorted to ground or
> floating?
>
> de WB2CPN
> Everything is somewhat resonant at one frequency or another.
> List includes folk guitars, planets in orbit, and wires that could
> be used as an antenna.  The trick is to make an unused wire,
> either horzontal or vertical, which is in your antenna farm, to be:
> (1) Grounded to prevent static change build up, and (2) Grounded
> in such as way as to cause its new resonant frequency to not be
> a frequency that you do have antennas for.   Shorted to ground
> via a capacitor is out, no Ohmic continuity.  So, shorted to ground
> via an inductance is the way to go.  If you leave it open, or shorted
> with a fairly high resistance, the wire becomes resonant at its
> natural half wave frequency.   The resistance short will help with
> the buildup of a static charge, but you still have no control over the
> natural resonant frequency.   I wonder what FCC says about
> the treatment of the vertical towers that are used for emergency
> restoration should their main tower fail.  I would expect that if
> the main tower is 90 degrees tall, you wouldn't want a smaller
> tower sitting nearby and resonant on the same frequency.
> Any ideas?
> 73  Clete
>
>
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