[AMRadio] Bug catcher questions

[Geoff Edmonson]

With a Henry Allen #680 bug catcher coil, and a (4) 2SC2879 Worthmore 
amplifier, I've managed (on SSB) to 'zorch' the bug catcher coil, about 
a half-dozen times, now.  Each time when SWR on the meter showed minimum.

Various things, I'm sure, caused each zorch.  One in particular was 
curious, as it was a carbon trace that arc'ed from the coil-form support 
to the top plexiglass 'end-cap', and RF energy poked a hole through the 
plexi. (I don't know that it's plexi or lexan, either way, it isn't 
"invisible" to RF.)

I've only had a corona ball off of the top of the whip, when I had an 
old original bug-catcher coil on my 91 Ranger, and a (2) 2SC2879 amp 
(~300w).  NEVER had a zorch on the coil.

Until yesterday, I had the coil mounted with the coil being tapped from 
the bottom up.  Time after time, when I ask if it matters, ham after ham 
said "it doesn't matter".  I'm not so sure.  The one ham I asked, is one 
of the most revered and respected (at least to me) in the world of 
Ham-dom, and is an Anchor of an AM guy.  When I asked John/WA5BXO, he 
said he tapped his bug-catcher (using an old Original coil by 
Alex/WA5UHT) from the top down.  Before I could ask why, the phone rang, 
and he was off again, maintaining his business.  I still don't have the 
answer, but I have an idea...

When I envision a 'jacobs ladder', the arc starts low and moves up.  In 
the one instance with the #680 coil, when I created a corona on the 
whip, the arc started at the top, and was working it's way down towards 
the top of the coil. (speaks well to the quality and construction of the 
600w Amplifier!).  I don't know that that matters.

The way I -think- things happen is, that as the voltage is applied at 
the bottom of the coil, tapping from the bottom, you basically have a 
-lot- of inductance on 75m (nearly the entire coil) and by the time it 
gets up near the whip, the voltage is WAY up there, and looking for a 
place to "jump"/arc.  If the coil is tapped from the top -down-, there's 
still just as much inductance, but at the top, where the voltage is 
looking for a place to 'jump'/arc, you provide a tap and that goes 
straight to the whip.  What do -you- think?

So far, so good.  No zorches, but that doesn't matter because I could 
re-work the coil and make it all better again, and run it for a month, 
or maybe two, without an issue.  Allofasudden, calamity ensues.

Is there a difference in tapping a bug-catcher coil from the top or bottom?

73 = Best Regards,
-Geoff/W5OMR (/m5 Houston)