Topband: Termination Transformer

n0tt1 at n0tt1 at
Fri Jan 1 20:01:34 EST 2016


> A second question, the BN-73-202 cores I use are conductive to a 
> small extent.  I have read it is better to use insulated wire or use 
> sleeves in the cores.  

You should use either enameled wire or something
like the wire-wrap wire that Radio Shack (used to?) sells.
See below on how I use enameled wire.

/>I noticed there was about 2.5K ohm between 
> the core and any of the windings.

Your winding is shorted to the core and there
could be even a shorted turn.  

> I assume some of the insulation 
> go scrapped off the enamel on the wire I was using.  

Yes, that's what edges at the
ends of the holes can slice right through enamel.

> I am moving to 
> insulated wire although that limits the number of turns.  

Use the wire-wrap wire or "Kynar"'s #30 with a thin,
tough insulation....could be Teflon.  A small diameter probe,
something like a toothpick, will help pack the wire in the 
core if your need a lot of turns. 

On using enameled wire...I insulate the holes in the cores
with ordinary plastic soda straws.  I cut them just a little longer
than the length of the core and then slit them lengthwise
with small sissors.  Then I roll them in my fingers, observing
how much excess there is in the "roll" when inserted into the
core, then I cut off most of that excess, leaving some overlap.
I re-insert the roll into the core and it's ready for use.

Charlie, N0TT

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