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 ;)
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.
> Jim K9YC
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