At 08:35 AM 1/4/2006, Tim Makins wrote:
>----- Original Message -----
>From: "Jim Lux" <firstname.lastname@example.org>
>Subject: Re: [TowerTalk] DRIVEN VERSUS PARASITIC 160 antenna
> > There's an even easier way to control the length with air power. Rather
> > than a knife switch, make the switch a plunger switch inside the
> > tube. Imagine a tube with an air cylinder in the end, and the ram poking
> > out. A short length of insulating tubing, and then the tubing for the top
> > of the antenna. The ram has one switch contact, and the bottom end of the
> > top element piece has the other. Extend the ram, and the two touch and
> > connects the end to the bottom. Retract the ram, and the top stinger is
> > disconnected.
> > This would also be a good way to use that liquid metal mentioned a few
> > ago. Rather than use the liquid metal to make the whole element, just use
> > it as a switching element to bridge a gap.
>Sounds like one of those tilt-switches from a pinball machine. They used
>mercury to bridge two contacts. Trouble is, on a windy day, you might find
>you were changing bands when you didn't want to...
You can do it very reliably. Not just a drop of liquid metal, you flood
the area between the contacts. take a look at how they do "mercury
contactors" used for quiet switching of big loads.
You can do it pneumatically, or by shoving something in to displace the
mercury up into the switching chamber.
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