[Amps] Ohmite thick-film resistor L measurement

[Dave Haupt]

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
them.

73,

Dave W8NF


>>R.Measures wrote:
>> •••   I need to find someone who can measure the L
of an Ohmite type TAP 
>> 600W, 100Ω 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?

>-- 
>73,
>Vic, K2VCO
>Fresno CA
>http://www.qsl.net/k2vco


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