I am trying to construct a broadband 4:1 balun, and I want to double
check if my understanding of the measurements is correct before I apply
any real RF power.

I do not have access to an antenna analyzer, though I do have an HP4193A
Vector Impedance meter and HP8753 Network Analyzer at my disposal.

First I wound the core in a bifilar manner with the leads being labeled
A1,B1 and A2,B2. Then I measured the input impedance across A1 and A2
leaving B1 and B2 unconnected. Then placed a 200 ohm resistor across A1
and B2 while tying B1 and A2 together, and measured across A1 and A2
looking for 50 ohms (4:1).

I have also seen a reference to a K value for an indication of
broadbandness. K = 1 - L(short)/L(open)

Here are my results...

8 bifilar turns of teflon coated AWG 16, on Type 43 core.

Mhz A1-A2 Open Impedance A1-A2 200 ohm Impedance
2 941 @ +59.5 51.4 @ 3.6 (51.3 +3.2j)
4 2080 @ -25.6 51.7 @ 3.2
7 4130 @ -74.2 52.1 @ 3.7
10 2900 @ -81.5 52.3 @ 4.4
14 1687 @ -84.8 52.4 @ 5.6
18 1180 @ -86.1 52.5 @ 6.8
21 966 @ -86.7 52.6 @ 7.7
25 781 @ -87.2 52.7 @ 9.1
28 682 @ -87.3 52.6 @ 10.2
30 630 @ -87.5 52.7 @ 10.8 (51.7 +9.9j)
-------------------------------------------------------------
50 356 @ -87.0 52.8 @ 18.6
54 327 @ -86.2 52.8 @ 20.4 (49.5 +18j)

Inductance Open = .93 uH
Inductance Short = 167 uH
K == .994

I did not intend to operate this balun above 10m, but thought it would be
interesting to see the 6m data as well. And it looks like it would work
fine there as well.

From what I have read, the open reactance should be at least 4 to 5 times
as high as the normal drive impedence. In this case, it is over 12
times the 50 ohm input at 30Mhz and over 6 times at 54Mhz.

So did I do good? Am I way off?
How can I tell if/when core saturation will be a problem?

--Teh