[Antennas] "fingerstock" -- Is it really 'dangerous' ?

[Christopher Boone]

Fingerstock is usually copper cut to look like a comb (hence the term 
fingerstock) which allows a moveable part to maintain connection with a 
fixed part of a tuning ckt. The fingerstock is connected to one section 
and its fingers are bent in a way to allow it to move without binding..
cavities in duplexers, etc have fingerstock in them to allow the main 
bandpass tuning adjustment to be made while maintain RF continuity..
It is NOT dangerous and a regular part of RF plumbing....there is NO 
toxic parts used (I read someone said berrylium? nope...not in 
fingerstock...just silver plated copper or aluminum is all that is needed!)

THE one problem with fingerstock....it does not like RF applied across 
it at high power levels while tuning the ckt...this can cause the 
fingerstock to burn at a high voltage or current point...causing pits 
and poor contact/open connections....obviously in a RF ckt this is NOT 
what you want......BUT as long as LOW RF levels are used, tuning is not 
a problem..once the proper spot is found, the power can be raised to 
normal levels..Screwdriver antennas of course slide up and down to tune 
for resonance....doing so under more than a few watts could damage the 
fingerstock and render the antenna useless...

I have a 100KW RF switch at a FM site which uses fingerstock!! No, it 
doesnt like to switch when all three FMs are on...but under normal 
conditions, it works just fine....and has for many years (except the 
time it DID switch under RF and NO load...main antenna went bad and it 
tried to switch to the backup....but got stuck in an open position to 
both antennas!! can you say BURNT? :)

Chris
WB5ITT

A10382 wrote:

> I've seen some adverts for screwdriver antennas where the manufacturer
> claims that their design: "does not use any of that dangerous fingerstock".
> 
> What's the issue with "fingerstock" ?
> How is it used inside the antenna and what is the potential 'danger' ?
> 
> ------
> I've had many types of antennas over the years.  At one time we did
> temporarily live (temporarily) in a 'restricted community' and did use a
> number of stealthy (actually sneaky) ways to get some sort of radiator up.
> However, I never had the opportunity to play with a screwdriver design.
> 
> 
> ====
> 73, Frank
>  ._._.
> 
> 
> 
> 
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