Homemade direct amplification receivers were once built by many. Nowadays, the manufacture of such a receiver will cause nostalgia in an adult, and a child during its assembly, perhaps, will forever join his father's hobby.
Instructions
Step 1
Assemble the receiver input circuit. To do this, wind several layers of tape on the ferrite core, and then place a winding on top of it, consisting of about eighty turns of a thin wire. Cover this winding with just one layer of tape on top so that it does not unwind.
Step 2
In parallel with the coil, connect a capacitor of variable capacity, the variation range of which is from 5 to 300 picofarads.
Step 3
Connect one of the terminals of the variable capacitor to the common wire through a fixed capacitor with a capacity of several nanofarads.
Step 4
Take an integrated circuit of the MK484 type (a modern analogue of the discontinued microcircuit of the ZN414 type) and place it with the marking towards you, and with the leads down. The left pin will be common, the middle pin will be the input, the right pin will be the output.
Step 5
Connect the output of the variable capacitor opposite to the fixed capacitor to the input terminal of the microcircuit. Connect its common output to the common wire of the receiver.
Step 6
Connect one of the terminals of the resistor with a nominal value of about 100 kilo-ohms to the junction point of the constant and variable capacitors. Connect its other output to the output pin of the microcircuit.
Step 7
Shunt the output with a nanofarad capacitor.
Step 8
Apply the plus of the power supply (1.5 V) to the output pin of the microcircuit through a resistor with a nominal value of about one and a half kilo-ohms. Connect the minus of the power supply to the common wire.
Step 9
Apply the output sound signal to ordinary computer speakers equipped with a built-in amplifier (they are called active ones) through a capacitor with a capacity of a few hundredths or tenths of a microfarad.
Step 10
Try to tune the receiver to a particular station. Change the number of turns of the loopback coil, if necessary. To shift the range in the direction of increasing the frequency, reduce the number of its turns, in the direction of decreasing - increase. Having finally adjusted the boundaries of the range, wrap the coil with several layers of tape.
