[TowerTalk] DRIVEN VERSUS PARASITIC 160 antenna

[Jim Lux]

At 05:06 AM 1/4/2006, Dennis OConnor wrote:

>I have actually cobbled up on the bench, an air powered knife switch to to 
>remotely control the element length...

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 days 
ago.  Rather than use the liquid metal to make the whole element, just use 
it as a switching element to bridge a gap.



>  It works just fine, is not sensitive to the high voltage RF fields at 
> the ends of the elements, and is not too expensive (relative term)... At 
> this point in time I have no great urge to go that that expense and work 
> just for convenience... For a flagship M-M contest station, the expense 
> is justifiable...
>
>Certainly, the driven 4 square arrays can be retuned with relays and 
>networks...
>
>denny - k8do

My personal goal is the rapidly field deployable phased array, so all the 
"tuning and fiddling" has to be computer controllable.  You don't have the 
luxury of getting out the ladder, adding a couple inches, dropping the 
ladder, going back to the shack and checking the meters, etc.