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[AMPS] My try at unravelling the knotty VHF-Rp Enigma

To: <amps@contesting.com>
Subject: [AMPS] My try at unravelling the knotty VHF-Rp Enigma
From: measures@vc.net (Rich Measures)
Date: Fri, 15 May 98 03:35:56 -0800
>Rich Measures wrote:
>>Using a  Hewlett-Packard Model 4191A RF Impedance Analyzer, Wes measured 
>>from 49 ohms to 169 ohms of Rp -- depending on test frequency for the two 
>>types of suppressors, both of which used a suppressor R of c. 100-ohms.   
>>It seems to me that Rp is Not the 100-ohm suppressor R.  . 
>
>> .  Am I wrong on anything so far?
>
>Rp is the APPARENT parallel resistance of the whole network, as measured
>between the analyser terminals. 
>
The numbers indicate otherwise.  

>In an idealized parallel R-L network (no other sources of losses, no
>stray inductances or capacitances) Rp would always be identical to the
>resistor value, at all frequencies. 
>
>In practice it is not. Losses in the L tend to make Rp lower. Stray
>inductance in series with the paralleled network tends to make the
>measured value of Rp larger (as I showed over the weekend, even a
>fraction of an inch of lead wire can have a major effect).
>
Is it reasonable that a 100-ohm suppressor R would measure:  100-ohms on 
a DMM,  49-ohms at 10MHz (where Ls losses are minimal), 102-ohms at 
100MHz,  and 104-ohms at 200MHz?  .   If lead-length were causing an 
appreciable effect, it would have produced a substantially different 
result.  


Rich...

R. L. Measures, 805-386-3734, AG6K   


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