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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: G3SEK@ifwtech.demon.co.uk (Ian White, G3SEK)
Date: Thu, 14 May 1998 22:41:21 +0100
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. 

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).


73 from Ian G3SEK          Editor, 'The VHF/UHF DX Book'
                          'In Practice' columnist for RadCom (RSGB)
                           http://www.ifwtech.demon.co.uk/g3sek

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