What appears to be missing in the picture you painted is the usual
choking device to decouple the unbalanced feedline from what otherwise
is a balanced antenna.
One could construct a balanced feedline switch and use various kinds
of balanced feedline arrangements, but...
That doubles the number of switch points needed, and generally runs up
complexity, and cost.
The usual commercially available switching arrangements for coax
presume that feedline current has been choked off and only
single-ended switching arrangements are required.
Presuming that is generally not an issue because unwanted radiation
from feedlines picks up noise, fouls impedances, and other weirdness.
People are already using baluns, feedline chokes, etc, for those
significant reasons.
So the manufacturers continue to construct single-ended unbalanced
switches.
It isn't to switch or not to switch, it's to choke or not to choke.
73, Guy.
----- Original Message -----
From: "Ford Peterson" <ford@cmgate.com>
To: <Towertalk@contesting.com>
Sent: Thursday, May 30, 2002 11:48 PM
Subject: [Towertalk] Remote Switches
> Until recently, I was using a remote switch on my tower (it fell a
couple of
> weeks ago). In looking at a design to replace it, I want to
incorporate a
> remote switch. Several manufacturers seem to make what appear to be
widely
> accepted devices. They all have one serious flaw as far as I'm
concerned.
> 1/2 of all the antennas are DC connected at the switch chassis
permanently.
>
> On my old system, the box was mounted at 67' or so. A short
feedline went
> to each of several antennas. In each case, the braid was connected
to one
> of the elements of the antenna. When you hook them to the switch,
they are
> all connected together through the chassis of the switch.
>
> On my 40 meter dipole, the RF in the shack was horrible. Think
about it. A
> 40 meter dipole mounted about 1/2 wavelength in the air. One side
(the
> braid side) is connected to a switch whose chassis is bolted to the
> tower--the chassis is 1/2 wavelength from a series of ground rods,
160 meter
> radials, etc. Does that make the 68' point a low impedance on 40
meters?
> Am I the only one having trouble with remote switches or is it the
way I use
> them?
>
> The fix in this case was about 20 type 43 beads on the feedline
between the
> switch and the 40 meter dipole. As far as I'm concerned, this was a
patch.
> That antenna never played well. The rest of the antennas (yagi, 3
dipoles,
> etc.) all had one side connected together through the switch. God
only
> knows what the pattern really looked like. Sure I could get a good
load on
> just about any band but God only knows what was really radiating...
>
> What am I missing here? To switch, or not to switch, that is the
> question...
>
> Ford-N0FP
> ford@cmgate.com
>
>
>
>
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