I.F. transformer frequency

Dear Friends.

Is there any way to find out the frequency of an IF transformer just with a RF generator?
I don't have an oscilloscope available at this moment....
Thanks in advance[.
Meyer

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Dear Meyer
If you have a Grid Dip Meter and know how to use it you can determine with a tunable RF generator.

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Dear Ernest.
As I don't have a grid dip meter available,

I'll try the configuration below, connecting one of the IF coils to the circuit's output and injecting a RF signal ranging from 175kc to 470kc.

When I get the maximum deflection on the micrometer I will have the IF frequency.

I'll do it this coming weekend and then I'll comment on the result

• ressonance checker (15 KB)

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Dear Meyer, the 50pF coupling capacitor will detune the IF transformer to a lower frequency. If this is a 455kHz tank, the internal tank capacitor is probably around 50pF too. Come to think of it, if the resonant tank is an FM IF tank that resonates at 10.7MHz, the resonant capacitor is also in the 50pF range. You should try, instead of the 50pF coupling capacitor, a high valued resistor between 100k and 1Meg. 

This detector arrangement does not allow for much voltage to be applied because the diode will present a heavy load to the tank with a strong test signal, so you will have to play with the generator amplitude to see the peak behaviour as you move the frequency back and forth.

A preferable circuit would have the RFC replaced by a 100k resistor with a small capacitor, maybe 50pF from the diode cathode to the ground wire in the diagram. Use as small a signal as possible to give a clear peak indication. A high impedance voltmeter is also preferable to the micro meter to reduce loading and maintain the sharp resonant peak.

Regards,

-Joe

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Yes, just with the mentioned RF-generator.

Receive f1; then increase the freq. of the RF-gen. untill you receive the signal at f3 , may be you have to increase the signal remarkable. Your IF frequency is (f3 - f1)/2.

In a shortwave band you eventually need no RF-gen. Tune to a strong station and try to receice the same signal as mirror frequency. If the scale  reading accuracy is not very bad, use the same calculation.

The short wave input selection is usually not very high, so it should be possible.

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Dear Joe.
You're right. I didn't really consider the IF internal capacitor...
But this circuit is not intended to have a lab precision, it was just to get an approximate value of the resonance frequency.
Anyway, the experience was satisfactory. Examining one IF, the resonance indicated on my generator was something close to 200 kc which leads me to believe that it is a 175kc IF.
When I can, I will try to implement your suggestions and compare the results.
Thanks you for your suggestions.

Meyer
 

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