[BC] Saving Your Own Life /was/ Tech. competence

[Phil Alexander]

On 12 Oct 2005 at 12:41, cldube wrote:

> Great tutorial Phil!
> 
> And may I respectfully add, have a voltage sniffer probe on hand as well.
> It might help you to discover that "mod" that was done 20 years ago
> that brings 110V (or more) into a particular part of the cabinet
> for a now obscure and unsuspected reason. As always, test the probe
> on a known voltage source (often rubbing it across your shirt will light it 
> up) to be sure the battery
> is in working order. Be sure your test equipment is a known "good".


Good catch Chuck. :)

A sniffer is one of the greatest tools you can have in your box. I use
and heartily recommend Barry's RG sniffer. The only problem is sometimes
it's not where it should be. (In a shirt pocket at home rather than in the 
one I have on.) And it is less destructive than the j-stick where those
"alternate" AC feeds are concerned. (The fuse you need is always the one
that should be in the empty box. - The umpteenth corollary to Murphy's Law.)

However, all things considered, I'll let the j-stick complete the circuit
before I touch it even if the sniffer can't "smell" a field. 

There is one thing you have to watch for in AM where the sniffer can save 
creating a problem. RF contactors usually are hot wired and work by 
momentarily grounding a lead. If a contactor lead runs into a Tx, grounding 
the lead may switch the contactor to the dead Tx you are working on and take 
the station off the air if the contactor control circuitry is - I'll be polite
and say - rudimentary, as some I've seen. I'd never wire one with a momentary 
ground to the contactor from the PA "ON" circuit, but some seem to like it 
that way. <shaking head sadly>  The sniffer will find that the easy way,
without taking the station off - and believe it or not, there are SOME AM's
where that still matters, especially if happens during a spot, or worse,
during a book.


Phil Alexander, CSRE, AMD
Broadcast Engineering Services and Technology 
(a Div. of Advanced Parts Corporation) 
Ph. (317) 335-2065   FAX (317) 335-9037





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