On Mon, 13 Nov 2006 14:25:52 -0800, Roy Lewallen
wrote:

How are you connecting it to measure the common mode impedance? I don't
think you can just connect the input leads together and output leads
together like you do with a 1:1, but I haven't taken the time to think
much about how you really should measure it. . .

Roy Lewallen, W7EL

Yes, I measured with the leads connected together as you described.
However, after I posted my question this morning I looked around and
found I had an Elecraft BL-1 current balun. This balun can be
connected as a 1:1 or 4:1 by just moving two wires on the circuit
board - no other changes are necessary.

I measured the BL-1 in both configurations, using identical methods
which show close agreement.

You can see the results at: http://k6mhe.com/elecraft.html

Danny, K6MHE