Step 3, building the second and third 455KHz IF

Note: The 2 nd and 3 rd IF may need a load to function properly; you may need to put IF-301's secondary from the "in" side of the capacitor to ground for testing and alignment if your signal generators probe has high impedance.

Third IF:

This circuit filters all modulation except for 455 KHz, and accounts for a good majority of the selectivity of your radio.

Connect the IN to the signal generator, and OUT to the oscilloscope at 1 us timing, and 0.01 volts sensitivity.  You will need to adjust the signal generators output so that it doesn't overload the if amp.

IF 303 is the Third IF, and IF 302 is the second IF transformer, but  build and test them the same (but one at a time).  Don't mix up the transformers!

Testing and alignment:

Move the signal generators frequency across 300 - 500 KHz it should have a sharp peak around 455 KHz,  if yours does not peak your circuit is not functioning properly.

Remember however I said around 455KHz, you will need to adjust the core to get it perfect.

Once yours peaks set the signal generator at 455 KHz and adjust the core to maximize the waveform.

You will need to adjust the output of your signal generator while doing this so it is not overloading the amp; keep turning the gain on the generator down, while tuning the core of the IF stage, continuously maximizing your waveform.

Second IF:

Do these steps for the second IF and build them as close together as possable; after this connect the Second IF's output to the Third IF's input.  The signal generator should be put on the Second IF's input and the oscilloscope shoud be on the Third IF's output;  realign at 455 KHz.

You may have to adjust IF 302 and 303 a few times before they are in sync,  You will notice that after the alignment, the noise at the bottom (when the signal generator is out of tune) is now almost non exsistant.

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