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Re: LF: G4HUP aerial current meter/ hazards

To: [email protected]
Subject: Re: LF: G4HUP aerial current meter/ hazards
From: DK7FC <[email protected]>
Date: Sat, 05 Aug 2017 10:47:59 +0200
In-reply-to: <[email protected]>
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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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