I'm with you, Ian. Someone on this reflector very recently stated the
basic, fundamental definition of "Q" as "(energy stored)/(energy
dissipated)." I think "per cycle" is usually added. Ultimately that comes
down to the very general form of X/R or R/X.
Seems to me the fundamental fact Rich continues to ignore is that you can't
define a loaded Q, which is what we're inherently dealing with in matching
networks, without including the dissipative element(s). Since the unloaded
"Q" of individual network L & C components typically is >>10X the loaded
"Q" of the network, for practical purposes (at least in high power Class
AB-B-C vacuum tube amps) the load which the network feeds IS the only
significant dissipative element. So of course "loaded Q" calculations must
be made with the load R in place. If you can't calculate impedance
transformation or network loaded Q without specifying RL, why in the world
would you try to figure resonant frequency without it?
If unloaded Q of the network inductor is less than ~100X the loaded Q of
the network, ignoring it (inductor Q) will introduce a small error into
loaded Q and impedance calculations. Without trying to be rigorous, I'd
guess that the resultant error percentage is roughly ~100 x QL/QU -
typically 1 or 2% max.
Ian? Peter?
Cheerio,
Dick W0ID
-----Original Message-----
From: Ian White, G3SEK [SMTP:G3SEK@ifwtech.demon.co.uk]
Sent: Thursday, August 05, 1999 4:13 PM
To: amps@contesting.com
Subject: Re: [AMPS] Pi-Net math
Rich Measures wrote:
>>>? There is more than one way to figure Q.
>>
>>Evidently - like to tell us your definition?
>>
>? I don't have one. Eimac defines Q as the ratio between RL and the
>reactance of C1. None of the Eimac formulae can be used without choosing
>a value of Q - as defined by their definition
>.
I can't believe I'm reading this. If you truly believe that the
definition of a quantity like Q is something that can change according
to whose pi-network formulae you use, then - I'm sorry, but it has to be
said - you literally don't understand the first thing about circuit
analysis.
>>The definition I'm using is Q = XL/Rs, where Rs is the transformed
>>effect of all resistive components, when made to appear in a series loop
>>with L.
>>
>? A definition which does not work with Eimac's formulae.
>
I still can't believe I'm reading this!
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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