On Feb 18, 2025, at 3:51?PM, Brian Beezley <k6sti@...> wrote:

?If you use a VNA to characterize devices such as IF transformers, crystal filters, or ceramic filters, normally you add series resistance to the 50 ohm VNA ports so that the device sees its design impedance, which is usually much higher. This lets you measure the true response, but the resistors will reduce the dynamic range. You can use matching transformers instead of resistors to avoid this, but you may not have what you need on hand. The transformers must have enough bandwidth not to affect the device response.

I've written a little program that renormalizes the S-parameter reference impedance to whatever the device needs. This lets you make a 50 ohm measurement and then see how the device would respond had it been driven and loaded by the correct impedance. If you record all four S-parameters, the renormalization will undo the effects of improper filter source and load impedances even for devices that are not perfectly symmetrical (reversing them changes the response). However, the program assumes the proper renormalized impedance is the same for input and output. This is not true of some IF transformers, for example.

The renormalization program is listed at the top of this page:

http://ham-radio.com/k6sti/mu.htm

See the bottom of the page for downloading instructions.

Brian