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Date: Sat, 05 Aug 2017 10:47:59 +0200
From: DK7FC <selberdenken@posteo.de>
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References: <0883B95D3F4D417F975C59A900E1A838@gnat> <alpine.DEB.2.11.1708042259310.734@mailn.lipkowski.org> <3D9A092BFA65418DBEE13188A4C58580@gnat> <92ce2c22-a887-bb8f-6bc2-6f03b51899d6@t-online.de>
In-Reply-To: <92ce2c22-a887-bb8f-6bc2-6f03b51899d6@t-online.de>
Subject: Re: LF: G4HUP aerial current meter/ hazards
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Status: RO

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
>