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[Amps] RE : Ohmite thick-film resistor L measurement

To: "'Dave Haupt'" <>, <>
Subject: [Amps] RE : Ohmite thick-film resistor L measurement
From: "hermans" <>
Date: Thu, 22 Dec 2005 00:20:44 -0000
List-post: <>

KISS .......but here S stands for SMART.

Jos on4kj 

Merry XMS and Happy 2006 to ALL

-----Message d'origine-----
De : [] De
la part de Dave Haupt
Envoyé : mercredi 21 décembre 2005 22:28
À :
Objet : Re: [Amps] Ohmite thick-film resistor L measurement

Series L could hardly be easier in this case.  You can
even use your rig, assuming it's broadbanded.  

Use the 100 ohm resistor as a load.  At low
frequencies, it will measure SWR=2:1.  Raise the
frequency until you see the SWR rise to some
convenient value at which you trust your measurement
device - 2.5:1 or 3:1 for instance.  Assume the rise
is caused by series inductance.

Now, plot the SWR=2.5:1 or SWR=3:1 circle as
appropriate on the Smith Chart.  Follow the Rnorm=2.0
line up from the X=0 line until you hit the SWR circle
you've drawn.  Read off the Xnormalized, and a few
little multiplies and divides and you'll have the
series inductance.

Alternatively, an RF sig gen, a one ohm carbon comp

1/4 watter and a two-channel scope can do it the
old-fashioned way by measuring V and I and dividing


Dave W8NF

>>R.Measures wrote:
>> ???   I need to find someone who can measure the L
of an Ohmite type TAP 
>> 600W, 100&#937; thick-film resistor.  This resistor
will be used for R-supp 
>> in a QRO VHF parasitic suppressor R&D project.

>Unless the reactance is greater than about 650 ohms,
you should be able 
>to use an MFJ or similar antenna analyzer -- it will
tell you R and Z 
>(or L).  Am I missing something?

>Vic, K2VCO
>Fresno CA

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