Topband: Termination Transformer

[Mike Greenway]

I was reworking my two wire beverage and re-examining some of the reasoning for my construction.  Regarding the termination transformer, ON4UN comments in his latest book Pg 7-88, “As we are dealing with nominal impedances that are higher than low-z coaxial cable impedances, we shall multiply the last number by 2, which will mean that n1 will be 8 turns with center tap and n2 will be 6”..  The original computation was for 4 turns n1 with center tap and n2 was 3.  Not being an engineer and I not sure why the doubling of the turns is needed.  The ratio stayed the same since both the primary and secondary got doubled.          

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.  I noticed there was about 2.5K ohm between the core and any of the windings.  Not sure if that really detrimental but I don’t like it.  I assume some of the insulation go scrapped off the enamel on the wire I was using.  I am moving to insulated wire although that limits the number of turns.  I guess the question is how bad does the resistance from different points on the winding to the core affect things being in the 2.5 K area?