Topband: impedance transformer windings

[Steve Flood]

I've been trying to put together an impedance transformer on the Amidon BM-73-202 binocular core.  It is to be used on a flag RX antenna for 160m so I need about a 950:50 (19:1) transformation.  The published AL is 8500 mH/1000 turns.  This translates to 8.5 mH per turn.  From a Handbook formula, I calculated I need 1.4365 mH on the HI Z side and 0.0765 mH on the Lo - Z  side.  As you can see, even one turn thru the core exceeds these by a large margin.  Do I need a core with a lower AL?  Seems like many folks recommend the BN-73-202 though with a 3:12  (W7IUV) or 1:4 (W8JI) turns.   But I can't arrive at these numbers by equation.  I'd like to learn how this works rather than just build it without learning.

  Thanks all.  Steve KK7UV.