W7TI says
>I've heard that "non-inductive" resistors are wound with one
>resistance element spiraling right handed and a separate one spiraling
>left handed. The idea is the inductance is supposed to cancel, but
>the winding is never perfectly symmetrical, so it doesn't. I don't
>know if that's what you've got, but I'd beware of them.
This is the 'Ayrton - Perry' method of winding, one of the uses for
which was producing very low inductance RF resistors for signal
generator attenuators by people like General Radio and Marconi
Instruments. It works very well when the resistors are wound on strips
of mica, so that they have a minute diameter. As Bill says, they're not
perfectly symmetrical, but having said that, I've got some 50 watt
chassis mounting 50 ohm resistors, and they measure out at about 85nH,
which is of the same order as you'd expect from that length of 20 gauge
wire (about 3.5 inches). A point that Rich made should not be forgotten
- the pure physical length of a resistor gives it inductance. And 100nH
in series with 50 ohms is about a 1.45:1 SWR at 30MHz
73
Peter G3RZP
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