Jim,
It renormalization doesn't change the Q in the measured test circuit, but it can compute what the Q would be at the new impedance.
The S parameters are a complete description of a linear 2-port, allowing (with enough calculation) the prediction of the 2-port behavior in any impedance environment.
--John
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On Fri, Feb 14, 2025 at 05:31 PM, Jim Lux wrote:
But renormalization just changes the calculation for the S parameters.
It doesn't fix the change in Q.
-----Original Message-----
From: <nanovna-users@groups.io>
Sent: Feb 14, 2025 4:20 PM
To: <nanovna-users@groups.io>
Subject: Re: testing non-50 ohm filters was Re: [nanovna-users] NanoVNA port
renormalization
Jim,
Of course the change in termination impedance changes the filter response. The
point of the renormalization is that the response can be recalculated to show
what it would be at the different impedance. Doing so requires knowledge of
the transfer function and the impedance of both ports.
Similar case: If you know the open circuit voltage and output impedance of a
source, you can compute its output level into any impedance.
--John
On Fri, Feb 14, 2025 at 09:42 AM, Jim Lux wrote:
Since most filters are a series of resonators of some kind or another,
terminating them in a resistance other than the design resistance will
probably change the filter characteristics. Consider a filter that
effectively
has an input that is a RLC circuit, where the R is the terminating impedance
of the source. If you change R from, say, 300 ohms to 50 ohms, then the Q
will be different. That will certainly change the skirts, and will also
probably change the overall passband (since most filters are stacked up
responses of multiple resonances).
