AM Radio

I built an AM radio receiver to understand the principles of radio communication. AM was chosen because it is simpler to work with a single frequency at a time.

For this project I used the following:

• Ferrite rod
• Enamelled copper wire
• Variable Capacitor
• TA7642 Radio receiver IC
• Transistor C1815
• Germanium Diode
• High Impedance Earphones
• Resistors
• Power Supply
  

Schematic Diagram

Circuit Description

The core of the circuit is the LC tank circuit, formed by the ferrite-rod coil and the variable capacitor. This combination resonates at a frequency given by:

\( f = \frac{1}{2\pi\sqrt{LC}} \)

By adjusting the variable capacitor, the receiver can be tuned to different AM stations.

To receive AM broadcasts in the United Kingdom, the LC circuit must cover the medium-wave (MW) band, which ranges approximately from 531 kHz to 1602 kHz.

For tuning across this band with an inductor of 330 µH, the variable capacitor should range between 30 pF and 272 pF.

The inductor was made by winding enamelled copper wire on a ferrite rod, resulting in an inductance of about 330 µH. A variable capacitor with a range of 100 pF to 500 pF was used, which is sufficient for receiving all AM stations within the MW band.

The output of the tank circuit is connected to Pin 2 of the TA7642 IC. The IC performs RF amplification and detection and operates best at around 1.5 V. A voltage divider provides this level of supply voltage. Because the current requirement is low, this method is adequate.

The detected audio signal from the TA7642 is amplified by a C1815 transistor. The output drives high-impedance earphones, which are connected between the collector of the transistor and the positive supply.

Results

After assembling the circuit, I adjusted the variable capacitor while listening through the earphones. Several AM broadcasting stations were receivable in the area, including a station in Guildford operating at 1566 kHz.

This prototype was then made on a Zero PCB

Then I made a PCB out of it