Hi Wolf yes the problems of unknown cores noted. Thetypes supplied in the
kits have been tested. We have not seen fracture but if you modify the
circuit for higher power it is a point to bear in mind. There seem to be a
wide range of core quality and parameters sold in this format. Motto "if it
gets warm it is lossy" :-))
Thanks and Best Wishes
Alan
G3NYK
----- Original Message -----
From: "Dr. Wolf Ostwald" <[email protected]>
To: <[email protected]>
Sent: Saturday, August 05, 2017 6:38 AM
Subject: LF: G4HUP aerial current meter/ hazards
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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