[Amps] Need some 220K 2 watt carbon resistors

Gary Smith wa6fgi at sbcglobal.net
Wed Mar 29 17:16:23 EST 2006


Thanks Ian.
Now,  "back to the (dusty) books" re how to plug in all of the numbers. 
Will be using some stuff (grey matter?) that I haven't used in years. to me, 
this is with this forum is about.
Also , now I have to learn about vector analysers.

Knowledge and the spreading about of it.
73,
Gary...wa6fgi



----- Original Message ----- 
From: "Ian White GM3SEK" <gm3sek at ifwtech.co.uk>
To: <amps at contesting.com>
Sent: Wednesday, March 29, 2006 12:51 PM
Subject: Re: [Amps] Need some 220K 2 watt carbon resistors


> Gary Smith wrote:
>>How can one see/read/find out as to how low the inductance of a
>>particular resistor might be? Am not trying to open a can of worms
>>here, am well aware that as a resistor heats up its inductance changes,
>>but... ?  Larger wattage values= less inductance to what might be
>>referred to as the "point of diminishing returns?" No flaming please,
>>yes, I should know the answer to this one but I do not.
>>That is why I am asking.
>
> Scrape off enough of the paint/cement/enamel to be able to count the
> number of turns (n). Measure the diameter (d) and length (b), and then
> plug the numbers into the usual formula:
>
> L = d^2*n^2/(18*d + 40+b)   uH (inch units)
>
> It would need a vector network analyser, used with some care, to measure
> the inductance more accurately than you can calculate it.
>
>
> -- 
> 73 from Ian GM3SEK         'In Practice' columnist for RadCom (RSGB)
> http://www.ifwtech.co.uk/g3sek
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