-----Original Message-----
From: Peter Chadwick <Peter.Chadwick@zarlink.com>
To: Steve Thompson <g8gsq@qsl.net>; amps <amps@contesting.com>
To: <amps@contesting.com>
Date: 19 February 2002 13:09
Subject: RE: [AMPS] Power out indicator
>Steve said:
>
>>I'm wide open to correction here, but I think If you are matching between
>>two resitances, the L match has the lowest loaded Q.
>
>
>Don't follow that one. In the L network, the Q is fixed by the impedance
>transformation. In the pi or the T (one of which is the dual of the other),
>having the three variables allows Q to be a chosen parameter.
>
>Although I suspect we may have to define what we mean by the circuit Q
here -
>the usual trick in a pi is that it's Rin/Xc1.
Maybe it's in the definition, but I think you can't have any Q you choose in
a pi network - isn't there a minimum value?
If you plot the matching on a Smith chart, and add some constant Q curves,
you can identify the point where highest Q occurs - I've always assumed that
point is the loaded Q of the network. If you do that for two resistances,
you find that a pi or T cannot have a lower loaded Q than the L network.
Having done a couple of quick doodles, I think it applies to any pair of
impedances.
Steve
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|