Measuring on intermediate frequency transformer (IF) for Medium wave (MW).

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MF tuning animation

Dependency of the resonance frequency on the position of transformer core.
Yellow transformer Turn left (up) IF Turn right (down)
Core turn [deg] -360-315-270-225 -180-135-90-45 0+45+90 +135+180+225
Resonance frequency [kHz] 501498494489483477473467 455447437423399397
inductivity [µH] with C=200pF 500        600     800

4 MW IF Transformers IF transformer in pieces

Left picture is a typical stuff of cans in an MW radio: red-oscillator, yellow-1.IF, white-2.IF, black-3.IF.
The IF transformers have their capacitors on the bottom part of the can - visible on the right picture.

From table values we see, that the core position has to be adjusted accurately.
Otherwise the strength of output signal and selectivity will be reduced.

Different shapes used for IF transformers:
IF transformer shapes
The parallel capacitance can be placed in a cave at the bottom of the transformer, but not always.
The value at AM radio for 455 kHz is often 200pF, but also 500pF, 1000pF and even more.
At FM radio for 10.7 MHz by L=4.4 µH is it 50 pF, also lower values are used in combination with larger inductances.

Reminder: fres = 1 / (2*π*√L * √C)
The reciprocal racio of fres from L and C is weakened due to the square roots over L and C.

Worked with:

Resonance frequency of a yellow MW IF transformer.

I used a sinus generator with sweep facility and a standard scope with external triggering possibility.
The probe capacity with a probe set to 10:1 is about 10pF, which causes shift of the resonance frequency,
because it is parallel to the 180 pF built-in capacitor with a 680µH inductivity coil.
It shifts the 455kHz down to 443kHz.

connection   IF generator   oscilloscope

Worked with:
function generator Rigol DG4062,
oscilloscope UNI-T UTD2102CEL.