[TowerTalk] Baluns/tutorial/notes.

Steve Hunt steve at karinya.net
Sat May 22 08:46:58 PDT 2010


Thanks for that. Your explanation encouraged me to go and re-read your 
paper. As always it was a "good read". Did I see some significant 
changes from previous versions:

1) Earlier versions of the paper stressed that 1:1 current baluns wound 
with bifilar windings rather than coax would suffer significant losses 
and heating because of flux leakage - I believe 30%-40% was mentioned. 
The paper encouraged us to experiment by building a 1:1 balun with a 
bifilar winding and noting the temperature rise when operating into a 
well matched load. It was a view which always drew a lot of "flak" if I 
ever quoted it on a forum.

All of that material seems to be missing from the latest version of the 
paper. In fact it seems to say something quite different - that bifilar 
wound chokes don't suffer high losses and that "When wound with parallel 
wires, the core sees the sum of flux from currents of opposite polarity; 
the differential components cancel, leaving only the common mode flux 
(due to the imbalance in the system)."

That seems to be a sea change - or did I misunderstand?

2) I believe the section on current baluns with impedance 
transformations other than 1:1 is new. Earlier in the paper you warn 
quite strongly that the flux in the cores of voltage baluns is directly 
dependent on the differential-mode signal; I was surprised not to see 
the same warning relating to current baluns in that new section.

Again, perhaps I misunderstood .... it has been known ;)

Steve G3TXQ

Jim Brown wrote:
> On Sat, 22 May 2010 15:08:50 +0100, Steve Hunt wrote:
>> Given the importance of having resistive (lossy) chokes, I wonder how 
>> you determine the phase angle using your test set-up?
> I showed that in my tutorial. I plot the curve of Z vs frequency, then do 
> curve fitting for the parallel resonant circuit to get values of R, L, 
> and C. Not as elegant as a VNA, but it works. :)  This works for #43 
> (NiZn) without modification, but for #31 (MnZn), which can have two very 
> broad resonant peaks with a lot of turns, one must attempt to fit two 
> curves, one on the low end and one on the high end. The result is a very 
> rough approximation. See the early section of the tutorial where I showed 
> that the equivalent circuit is two parallel resonant circuits in series, 
> showed that some materials have both, some have only one, and then 
> compared #43 with #31. 
> As a very rough approximation, we can assume that the choke is 
> predominantly resistive if the Z is within about 30% of its peak value. 
> 73,
> Jim K9YC
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