Description.
This is the circuit diagram of the simplest single chip AM radio. The circuit is designed around the IC ZN414Z which is a ten transistor tuned radio frequency receiver .The IC has only three leads and is available in the TO92 package. All necessary circuits required for an AM receiver (RF amplifier, detector and AGC are incorporated inside the IC).In the circuit given below, capacitor C1 and resistor R1 forms the tank circuit which is essential for tuning. Capacitor C4 decouples DC from the output of the IC and C1 bye-passes the noise. Transistor Q1 and associated components forms a classic driver stage for the headphone. Head phone is connected across the resistor R5 and R4 gives necessary biasing for the transistor Q1.

Circuit diagram.

Notes.

• Assemble the circuit on a good quality PCB.
• The circuit can be powered from a 1.5V cell.
• Do not give more than 1.8V to the circuit as it will destroy the IC.
• For L1 make 80 turns of 0.3mm enameled copper wire on a 5cm long ferrite rod.
• K1 can be a high impedance crystal earpiece.

Description.
Circuit shown here can be used to jam FM radios in its vicinity. The circuit is nothing but a classic single transistor oscillator operating in the VHF region. Working principle of the circuit is very simple and straight forward. Powerful VHF oscillations from the circuit will interfere with the FM signals to nullify it. Jammer circuits like this are illegal in many countries and you must assemble this circuit on your own responsibility. This circuit is intended only for fun and i request you not to misuse it.
Circuit diagram.

Notes.

• For L1 make 6 turns of 16AWG enamelled copper wire on a 9mm plastic former.
• The circuit can be powered using a 9V PP3 battery.
• For extended range, use an antenna.
• A 30cm long wire connected anywhere on the coil will do for the antenna.
• For better performance, assemble the circuit on a good PCB.

Description.
This could be the simplest FM transmitter circuit you can find on the internet. Only using a single transistor and few passive components, this transmitter can deliver signals up to 50 meters. The transistor Q1 serves as the modulator as well as oscillator. Capacitor C2 and inductor L1 forms the necessary tank circuit for making oscillation. The voice to be transmitted is coupled to the base of Q1 using an electret microphone. The FM signal available at the collector of Q1 is radiated using the antenna.
Circuit diagram.

Notes.

• Use a 3V battery for powering the circuit.
• The circuit can be assembled on a Vero board.
• Coil L1 can be made by making 5 turns of 24AWG wire on a 1cm plastic former.
• Adjustments in the transmission frequency can be made by compressing or relaxing the coil.
• Antenna can be a 25cm long 18AWG wire.

Description.
Here is the circuit diagram of a simple and low cost AM radio. The working of this radio circuit is straight forward. Inductor L1 and capacitor C1 forms the necessary tank circuit. Diode D1 performs the job of de-modulation. Transistor T1 is wired as a preamplifier whose output is further amplified by the IC LM386 to drive the head phone Z1. The 10K POT R3 can be used as a volume controller.
Circuit diagram.

Notes.

• The circuit can be powered from a 9V PP3 battery.
• Use a 100cm long metal wire as antenna.
• Experiment with the value of L1 for catching other bands.
• The circuit can be assembled on a Vero board.

Description.
Here is the circuit diagram of an FM transmitter using the IC UPC1651. UPC1651 is a wide band UHF Silicon MMIC amplifier. The IC has a broad frequency response to 1200MHz and power gain up to 19dB.The IC can be operated from 5V DC.
The audio signals picked by the microphone are fed to the input pin (pin2) of the IC via capacitor C1. C1 acts as a noise filter. The modulated FM signal will be available at the output pin (pin4) of the IC. Inductor L1 and capacitor C3 forms the necessary LC circuit for creating the oscillations. Frequency of the transmitter can be varied by adjusting the capacitor C3.

Circuit diagram with Parts list.

Notes.

• The circuit can be assembled on a Vero board.
• Inductor L1 can be made by making 5 turns of 26SWG enameled copper wire on a 4mm diameter plastic former.
• A ¾ meter insulated copper wire can be used as the antenna.
• Do not give more than 6V to the IC.
• Mic M1 can be a condenser microphone.