Description:
The first
intermediate amplifier blocks out all frequencies except 10.7 Mhz,
and mixes the Local Oscillator and Antenna Filter together
Note: You must use a general purpose VHF transistor in this curcuit on the NPN transistor labeled "VHF".
1.
Build the
circuit shown on the right side with the 42IF129 transformer.
2. Attach a oscilloscope probe to the out side and ground it to negative close to where you built the circuit, set the scope to 0.01 Volts at a frequency of 0.1 uS per devision.
3. Put a signal generator on the “from AF” side and ground it to negative (you may want to ground out the "from oscillator")
4. Sweep across and there should be a peek around 10.7 MHz, if there is no peak there is something wrong with your circuit.
5. Set the
generator to
10.7 MHz and tune the core of the transformer maximizing the waveform
while turning down the output of the signal generator so the amp does
not overload.
2. Attach a oscilloscope probe to the out side and ground it to negative close to where you built the circuit, set the scope to 0.01 Volts at a frequency of 0.1 uS per devision.
3. Put a signal generator on the “from AF” side and ground it to negative (you may want to ground out the "from oscillator")
4. Sweep across and there should be a peek around 10.7 MHz, if there is no peak there is something wrong with your circuit.
5. Set the
generator to
10.7 MHz and tune the core of the transformer maximizing the waveform
while turning down the output of the signal generator so the amp does
not overload.6. Bind the second, third and first IFs together as shown on the left, and realign.
7. Connect the third if output to the FM Detector.
Note: the two 0.0036uf capacitors in the middle; Do not mix up the transformer polarities! They should always be reversed.