How can I make an AM wireless microphone? Can you suggest a website to find such schematic diagram for that?

Question

Our instructor in Electronics engineering gave us a project, that is, to make a wireless microphone that will transmit in AM bandwidth. Because this is our first design project, I don't know where to start. I even search the web for schematic diagrams for an AM wireless mike, but I couldn't find any, instead, only FM wireless mike.

Answer 1

An AM transmitter is just an oscillator whose output strength can be varied in response to some modulating signal  (in this case, audio from a microphone).

The simplest one-IC transmitter is this:  Wire five of the gates of a 74HC14 hex schmitt inverter in series, with a 1MHz crystal completing the loop.  Connect the input of the "spare" gate to one of the intermediate outputs and connect a 220 ohm resistor from the output of this gate to 0V.  Connect the antenna to the junction of the gate output and the resistor.  Connect a carbon microphone  (from an old telephone handset)  in series with the supply  (4 * 1.2V AA cells in series).

Modulation comes from the fact that the mic varies the voltage available to the oscillator  (but the crystal oscillator keeps running at a constant frequency).  The 220 ohm sink resistor is there to ensure that there is a severe current gradient everytime the oscillator switches.

Note: you will not be able to pick this up on a set with a digital tuner, because it broadcasts on 1MHz and digital tuners only go up in multiples of 9kHz.

Answer 2

that because fm is far more superior than am transmittion.