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Re: [Amps] Amps Digest, Vol 110, Issue 2

Subject: Re: [Amps] Amps Digest, Vol 110, Issue 2
From: "Dave" <>
Date: Fri, 03 Feb 2012 20:37:26 -0000
List-post: <">>
You can get some inductance reduction, by wrapping the resistor with 
copper foil, soldering it so it makes one huge shorted turn, somewhat 
reducing the inductance.  But it often compromises the cooling of the 

Passing a close fitting copper tube through the middle (if it's the type 
wound on a ceramic tube) that too creates a shorted turn effect, to some 
extent.  Plus, you can pass coolant through it.

Make sure with either, if there is HV involved on the resistor, that the 
insulation is OK.  The enamel on some is poreous, leading to some 

Of course, the frequency range of this sort of thing is limited, 
especialy at LF.  And at VHF, parasitic cpacitance to the foil or tube 
limits it's usefulness.

The few times I've tried, it seems to work best on larger wire wound 

Dave G0WBX.

> ----------------------------------------------------------------------
> Message: 1
> Date: Fri, 03 Feb 2012 09:23:20 +0100
> From: Angel Vilaseca <>
> Subject: [Amps] reducing the reactance of a wirewound resistor
> To:
> Message-ID: <>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> Hi all
> I have a nice large 50 ohms wirewound resistor, which I would like to
> use as a dummy load. Problem is, it is inductive of course.
> To cancel the inductive reactance I was thinking of winding some
> enameled wire all along over the resistor, with as many turns as the
> resistive wire, solder the enameled wire to the resistor terminal at
> one end and feed the RF at the other two separate terminals (wire and
> resistor) at the other end.
> The idea is that the inductive reactance of the resistor winding and
> the enameled wire winding will cancel each other. With some care and
> measuring gear the remaining reactance could be very low. The assembly
> would then behave almost as a pure resistance.
> Of course, care should be taken not to reach too high temperatures,
> because the enameled wire would then be damaged.
> Also, the added winding should be wound in the appropriate diraction (
> CW or CCW depending of the winding direction of the resistive wire)
> otherwise the two inductances would add instead ao canceling each
> other.
> Has anyone alredy tried this?
> 73
> Angel Vilaseca HB9SLV
> ------------------------------
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