Hi Roy,
> "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."
>
> Hi Tom,
>
> Well,
>
> I'm still running my T-400-A core in the PA tank as L1 in the PI-L net on
> 80M and did it on 160M for years at 1300 watts output. Have felt it after
> hours of CW use rag chewing and it was always at the ambient temp. in
> there like everything else.
Exactly Roy, and that illustrates the point I tried to make.
In a tank circuit, the amount of inductive reactance required is
typically in the low hundreds of ohms, in the output inductor of a pi-
L much less. The inductors are part of a system with low reactance
shunting capacitors, so the stray C of a toroid doesn't hurt the
system very much.
Toroids fit into some tank applications very well, even though
properly designed air-core inductors (if you have space) almost
always have higher unloaded Q's.
In loading systems requiring high amounts of inductance with very
little shunt capacitance, the distributed capacitance in a toroid (and
to a lesser extent core losses) make for very poor performance
compared to conventional inductors.
That's why we never see toroids in Q-critical systems requiring high
values of inductance when the toroid is operated without low
shunting capacitances in the external system, but they work OK in
tank systems, baluns, and other applications.
73, Tom W8JI
w8ji@contesting.com
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