Amps
[Top] [All Lists]

Re: [Amps] Measuring Q with an SWR analyzer

To: Bill Turner <dezrat1242@ispwest.com>, amps@contesting.com
Subject: Re: [Amps] Measuring Q with an SWR analyzer
From: Peter Chadwick <g3rzp@g3rzp.wanadoo.co.uk>
Reply-to: g3rzp@g3rzp.wanadoo.co.uk
Date: Thu, 5 Jan 2006 10:52:54 +0100 (CET)
List-post: <mailto:amps@contesting.com>
Bill asks:
>From this is it possible to calculate the Q of the tank circuit? 
Obviously, the higher the Q, the smaller the 2:1 SWR bandwidth, but 
is it possible to calculate it exactly?<
Yes. The accuracy depends on the accuracy of the measurement of the 2:1 VSWR, 
and the frequency.
Now, deriving the actual equations needs more consideration: the problem is 
that you know the SWR, but not actual impedance, so you're starting from a 
circle on the Smith chart, not a point.
As the math text books say, 'derivation is left as an exercise for the reader'.
An easier method would be to feed a signal in and measure the volts across the 
load resistor with a RF voltmeter (VTVM!) or 'scope or whatever, and measure 
the frequencies where the volts has dropped to 0.707 of the volts at resonance.
73
Peter G3RZP
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps

<Prev in Thread] Current Thread [Next in Thread>