Moin,
A current transformer without a secondary winding is no current
transformer but a simple coil. And most likely a bad one. Current
transformer is by definition a transformer that has nearly a short cut
on the secondary side. The higher the secondary impedance, the higher
the stress, just in opposite to a voltage transformer. But we konw that :-)
BTW, a simple "RIK20" from Reichelt,
https://www.reichelt.de/index.html?ACTION=446&LA=0 holds more than 10A
antenna current on 137 kHz, 'key down' (with 40 secondary turns and a 1
Ohm load behind a bridge rectifier), eeehm i mean current through a
dummy load in the shack of course....
73, Stefan
PS: Wow that was the deepest summer hole in the recent days since i am
member of this reflector :-) Is the new season starting now?
Am 05.08.2017 07:38, schrieb Dr. Wolf Ostwald:
good morning !
a current transformer with ferrites of unknown origin and virtues is a
very risky thing.
As these cores are widely available on swapmeets its a lure to use them.
But they can be tested. I blew a few of them by just putting them on
with a single primary turn and with power less than a hundred watts
they got hot and broke.
The losses can be extremely high.
It does not help to measure their magnetic constant. As that has not
much to do with frequency dependent losses.
a way to find out is to use a 50 ohm load and measure the RF voltage
across the terminals. Then u just put the toroid over the "hot" side
of the resistor terminals.
If the measured RF voltage drops heavily, the core is useless. You
dont want it to block, u want to derive some RF for measuring purposes.
The above core would go into pieces and additionally as it poses a
high inductance to ur feedline, the amplifier stage may go south,
depending on the safety factor involved with ur construction .
73 de wolf df2py
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