The figure referred to is using the material as part of an
RFI suppression choke where you want attenuation at RF
frequencies. I think you'll find that when the Type 61
material is used as a transformer, it will have very low
loss if designed properly.
Even 73 materials can have low loss if the transformer has
high enough impedance compared to the load impedance and it
is a true transmission line transformer, but materials with
a lower loss tangent are generally better if the transformer
has enough impedance across each winding.
I think that even a well-designed transformer will have
maybe 1-2% loss. At 100 watts, that is 1-2 watts which
will cause the transformer to heat up. Just dissipate
1-watt in a resistor with your DC power supply and feel
the heat.
It's all about the surface area and the dissipation. Many
even wrongly call heat "saturation", when it is almost
always nothing more than dissipation from the resistive part
of the impedance and the voltage across (or current through)
that resistance.
As a matter of fact most baluns and transformers operating
at more than a few watts heat long before they come close to
saturating. For example the balun in the ATR30 tuner
overheats to the point where it reaches the core temperature
limit at just 100 watts of dissipation for about one minute.
The heat is not caused by saturation unless you are running
a 30 kW pulse transmitter with low duty cycle into a
particular load. Heat is almost always caused by resistive
losses, and the balun will typically handle 2-3 kW of CW
without undue heating. 50 watts of loss out of 2 kW will
make it get VERY warm, but it is insignificant loss and not
saturation.
Put heat it into perspective of the applied power and the
area dissipating heat. Think of how hot a 7 watt light bulb
gets and the surface area of the bulb. Now think of a
standard 100 watt bulb, or a standard 40 watt florescent
lamp. All of them mostly make heat from the applied power.
It is a surface area and power dissipation problem so we
have to use common sense by comparing it to similar size
things.
A final thought. The worse way in the world to determine
balun efficiency is with a signal report. First, there is a
time problem on skywave. By the time we change baluns or
tuners propagation can change. Second, either locally or on
skywave any change in balance can change antenna patterns.
Groundwave is particularly USELESS with a horizontally
polarized antenna. I know of at least three tests where
people compared tuner or balun configurations on groundwave
using horizontally polarized antennas. The results of those
tests are meaningless, because a change in feeder unbalance
would significantly affect ground wave field strength. This
is because only the vertical component can propagate over
any distance along the earth, or does well near the earth's
surface. The worse system for balance will produce the
strongest local signal when using horizontally polarized
antennas at HF.
We have to be careful what we conclude or assume. Even when
we are careful and use good methods, there can be mistakes
or things we miss.
73 Tom
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