Date: Thu, 6 Jun 2013 09:06:16 -0400
From: "Carl" <km1h@jeremy.mv.com>
To: <jim@audiosystemsgroup.com>, <amps@contesting.com>
Subject: Re: [Amps] The Carl and Jim Show
Well at least JimVE7RF and I are still friends and we simply enjoy the
banter but on here there are those who get their knickers in a knot.
In your case you dont have 50 years experience but like to use others
information and call it your own and act as if ferrites, common mode/RFI/TVI
suppression is your own discovery. Sorry to dissapoint you but it was
already old when I was introduced to it in the 70's.
Carl
KM1H
## Beware of using small size coax, like RG-303 teflon types and also RG-58U,
when
a lot of turns are used on stacked type 31/ 43 2.4 inch OD cores. You can
easily get
parasitic arcing between adjacent turns. That happened with a buddy who tried
that
config, and placing it BEFORE a hb T type tuner, configured for balanced line.
He also
tried using 8 x type 43 cores, 4 on each side..and cooked the cores. Jay at
array solutions
warned me about using too many turns of small coax on XXX cores, even if the
choke is
at the feedpoint of a balanced ant..... you can get arcing between the last two
turns, at least with
serious qro.
## It’s a dumb place to try an insert a choke. W8JI was right, you need at
least a 50 k choke
Z if you try an put the choke in front of a T type tuner. Problem is, even when
configured for
balanced operation, the T type tuner is still not balanced, not even close.
The fix was to reconfigure
the T type tuner back to un-balanced operation..... then use coax on output
side of the tuner
to a 1:4 balun, then the 450 ohm line.
## what else that works is a balanced L type tuner, like you see on rich
measures site. That
type of tuner is truly balanced....and a choke can be inserted before the
tuner. Dunno if Rich
cooked it up or not, but I see that at least two manufacturers have ripped off
the idea.
## as far as Z going up to the square of N turns of coax through ferrite
cores, nothing new there.
About the only new thing is type 31. Dunno if type 77 is still available or
not.
## I find it amusing that when reading k9YC tutorials, power point
presentations, and everything else
he has available, that he always avoids feedline lengths of 1/4 wave and 3/4
wave, and 5/4 etc.
The feed point Z is sky high at those lengths. But these are physical
lengths..and not electrical. Then
you gotta shorten by 2%, to factor the stray C between coax and yagi boom.
The concept works good too,
but so far has only be used with yagis on top of a steel tower. Braid of coax
bonded to mast or top of tower,
then the 1/4, 3/4 wave of coax run from remote switch box to each yagi.
Then you don’t need a choke
balun at the feedpoint. A clamp on RF ammeter run up and down the main coax
will verify the effect.
## as far as the dreaded pin 1 problem on commercial audio gear when balanced
inputs are used, I have yet to
see any gear with a pin 1 problem. It has to be really old gear to have a pin
1 problem. Nobody would be stupid
enough to build gear with pin 1 problems these days, the gear would be sent
back asap.
Jim VE7RF
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