[AMPS] Non Inductive Resistors

[w8jitom@postoffice.worldnet.att.net]

> From:          Rich Measures <measures@vc.net>

> There is no such thing as a non-inductive resistor.  The resistors we use 
> in the suppressor retrofit kits (100 ohm, 3w Matsushita, MOF-type) have 
> about 10nH - according to Wes, N7WS.

The resistors you sell have a spiral winding of metal film inside, as 
do all MOF and carbon film types.

> The longer the resistor, the more 
> L.  A 100 ohm 100w globar-type has roughly 100nH [0.1uH]. 

100nH in a 50 ohm load resistor, a type common to dummy loads, would 
produce an SWR of 1.4 to one on 30 MHz, and 5.37 to one at 150 MHz. 

A good way to test the resistor would be to simply measure the VSWR 
change with frequency. Many people are "fooled" into thinking carbon 
or metal film resistors are all non-inductive, when many of them have 
considerable inductance. "Glo-bar" or carbon composition types 
(generally special order now) ALWAYS have much lower inductance when 
comparing the SAME power rating device as the metal film or standard 
type carbon resistors. 

73, Tom W8JI

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