> How about using an Amidon T-400-A powdered iron toroid core up there to
> shrink the physical size and wire length?
It depends on the end application. Most often, toroids are not
useful in a loading system.
Toroids work best in high-shunt-capacitance or low-impedance
systems. They have far too much distributed capacitance for
loading systems that require high values of loading reactance.
It's too complex to summarize for this reflector why, but air core
space wound inductors are almost always best. Q maxs out at
about 700 or so in an optimum design air core inductor.
Toroids are lucky to make a Q of a hundred unless the reactance
required is low, and they suffer from heating because losses are
concentrated in a small area that isn't exposed to airflow.
I generally don't plug things that are being sold, but "Antennas and
Transmission Lines" by Dr. John Kuecken (probably the best
antenna guy I ever met) has an entire section on loading reactance
design. At my urging, MFJ reprinted his book (which was used in
the 60's as part of antenna theory courses I took).
If you have a copy of any antenna theory book, you should have
this one.
73, Tom W8JI
w8ji@contesting.com
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