AM transmitter

[Cecilia]

Hi, I have some questions about the AM transmitter by Andy Collinson.
http://www.electronics-lab.com/projects/rf/011/index.html

1. What type of microphone it is used in the circuit. Is the normal microphone using for our laptop can be used?  What is the purpose of using the resistor R1 and capacitor C4?

2. Can i replace the C1 with smaller value of the capacitance?

Thanks!

[audioguru]

Hi Cecilia,
Welcome to our forum. ;D
The microphone is an electret type. It is shown as a 3-wires one but I have seen only 2-wires ones. We don't know which type is used with your laptop.
R1 powers the FET transistor inside the electrret mic.
C4 couples the mic signal to Q2 and blocks the DC.

Use a coil and tuning capacitor from an old AM radio so they match each other. If you reduce the value of C1 then the transmitter will tune to frequencies higher than the AM broadcast band.