I am trying to understand how radio IF transformers are characterized and specified. In the image above from a Mouser catalog are three different IF transformers with a center frequency of 455 kHz. The inductance for all is listed as 680 uH, but the impedances for both the primary and secondary windings are all different, for the primaries 20K, 30K and 60 K; for the secondaries 6K, 500 and 600. All three have a capacitor of the same value (180 pF) across the outer leads of the primary winding.
As I understand it, the IF transformers resonant at their center frequencies. The calculation for resonance for 680 uH and 180 pF gives 455 kHz.
I am guessing that the listed impedances are actually resistances, i.e., no reactance, at the center frequency of 455 kHz, and are altered from one IF transformer to the next by the number of windings and the nature of the yellow, white or black tuning slug.
I am at the stage where I don’t know what I don’t know. I have looked for a white paper on IF transformers and so far have come up dry.