This article teaches you how to create a simple AM Radio Circuit using easy to find parts like transistors, capacitors, resistors and an inductor.
These components are simple to get making it a fun way to explore basic radio frequency RF circuits, learn how to catch signals and boost audio sounds.
The circuit is designed to receive medium wave AM signals, recognize the amplitude modulated signal, and convert it into audio signals that are amplified and played through a small 10 ohm speaker.
This project is great for school assignments and for anyone curious about radio technology.
A 9V PP3 battery powers the circuit.
Remember before thinking to design this circuit you need to have a good signal strength as this circuit works best in areas with strong signals.
Circuit Working:
Parts List:
| Component Type | Value / Description | Quantity |
|---|---|---|
| Resistors (1/4 Watt) | 1M, 39k, 6.8k, 2.2k | 1 each |
| Potentiometer | 1k | 1 |
| Capacitors | Trimmer Capacitor 500pF | 1 |
| Ceramic 0.1µF, 470pF | 1 each | |
| Electrolytic 47µF 25V , 4.7µF 25V | 1 each | |
| Semiconductors | Transistors BC547, 2N2222 | 1 each |
| Speaker | 10Ω | 1 |
| Coil | 65 turns of 24SWG enameled copper wire on 100mm long, 10mm diameter ferrite rod; tapping on 5th turn | 1 |
The Simple AM radio Circuit have few stages for working:
- Tuned Circuit and Detector Stage
- RF Amplifier Stage
- Audio Output Stage
Tuned Circuit and Detector Stage:
The tuned LC circuit consists of coil L1 which has a winding of 60 turns and another with 5 turns along with a trimmer variable capacitor C1.
This part is essential for selecting the specific AM frequency signal we want to hear.
Transistor Q1 is configured to function as a regenerative detector.
This regenerative capability enhances both the selectivity and overall gain of the circuit.
Capacitor C2 connects the RF signal to the base of Q1.
Potentiometer VR1, R1 and capacitor C3 work together to stabilize and provide the correct biasing for Q1.
RF Amplifier Stage:
The detected audio signal is sent to Q2 transistor which serves as a Class A amplifier.
To establish the bias resistors R2 and R3 are used.
Capacitor C4 acts as a coupling capacitor blocking any DC while allowing the audio signal to pass through.
Audio Output Stage:
The amplified audio signal is delivered to the speaker via capacitor C5
Resistor R4 is crucial for balancing the load and managing the current.
And lastly 10 ohm speaker that produces the final audio output.
Formulas with Calculations:
Below are the formulas with calculations for Simple AM Radio Circuit using Transistors:
Resonant Frequency of LC Tank Circuit:
The tuned circuit L1 and C1 is responsible for selecting a specific frequency from the AM band.
Formula: f = 1 / (2 * π * √(L * C))
where,
- f is the resonant frequency in hertz, Hz
- L is the inductance in henries, H
- C is the capacitance in farads, F
- π is the Pi approximately 3.14159
Voltage Gain of Transistor Stage Q2:
Voltage gain Av for common emitter amplifier:
Av = Rc / Re
where,
- Av is the voltage gain (how much the input signal is amplified)
- Rc is the collector resistor (connected to the collector of the transistor)
- Re is the emitter resistor (connected to the emitter of the transistor)
Rc = R3 = 6.8k Re = R4 = 2.2k
Av = 6.8K / 2.2k = 3.1
This gain is sufficient to drive a small 10Ω speaker.
How to Build:
To build a Simple AM Radio Circuit using Transistors following steps are needed to follow to design your own circuit:
- Assemble all the components as mentioned in the above circuit diagram
- Connect the base of transistor Q1 to one terminal of resistor R2 and other terminal of R2 connect to emitter of transistor Q2
- Connect capacitor C1 from base of transistor Q1 and GND
- Connect capacitor C2 between resistor R1 and capacitor C1
- Connect L1 coil one end from capacitor C1 and other end to GND
- Connect the emitter of transistor Q1 to center pin of VR1 pot
- Connect the collector of transistor Q1 to the base of transistor Q2
- Connect the upper pin of VR1 pot to third wire of L1 coil and lower pin of VR1 pot connect to GND
- Connect resistor R1 and capacitor C3 in series from positive supply to GND
- Connect the collector of transistor Q2 to one end of 10 ohm speaker through capacitor C5 and other end of transistor Q2 to GND
- Connect resistor R4 from emitter of transistor Q2 and GND
- Connect the positive of capacitor C4 from one end of resistor R1 and negative of capacitor C4 connect to GND
- Connect one terminal of resistor R3 from positive of of +9V DC and other terminal connect between collector of transistor Q2 and positive of capacitor C5
Conclusion:
Simple AM Radio Circuit using Transistors shows the main ideas behind radio communication and how to make signals stronger.
With just a handful of parts the circuit can pick up and play AM signals.
This setup is great for school projects or for people who enjoy building radios as a hobby.
It is simple to put together and does not need any integrated circuits making it ideal for anyone who wants to learn about the fundamentals of analog electronics and radio frequency design.