• Skip to main content
  • Skip to primary sidebar

Homemade Circuit Projects

Get free circuit help 24/7

New Projects | Privacy Policy | About us | Contact | Disclaimer | Copyright | Videos | Circuits for Beginners | Basic Circuits | Hobby Projects | Transistor Circuits | LED Drivers 

You are here: Home / Meters and Testers / 1.5 watt Transmitter Circuit

1.5 watt Transmitter Circuit

Last Updated on January 24, 2020 by Swagatam 16 Comments

caution electricity can be dangerous

This little transmitter will allow you to communicate, chat, send music transmission on any standard FM Radio tuned within the existing band, across a radial distance of not less than 500 meters or half a kilometers.

Warning: Using this transmitter could be illegal in your country or area, take appropriate permissions before indulging.

How it Works

The circuit of this 1.5 watt transmitter is fundamentally configured for driving a tuned RF amplifier stage by an oscillator stage.

Referring to the diagram we find that the BC547 is rigged in a oscillator mode which resembles a Pierce oscillator circuit.

The base of the BC547 is biased by the 10k resistor, and the crucial RF coil is connected across the collector/positive of the transistor.

As soon as power is switched ON, this coil is resonated by the 20pF capacitor across the transistor collector and emitter.

The 33pF capacitor makes sure that the capacitance does not exceed the maximum specs of the design.

The above capacitor also determines and fixes the working band frequency of the circuit which is within 80 MHz and 110 MHz.

The varicap diode is included in order to convert the fed input voice or music signal into riding electrical pulses over the carrier frequency created by the above discussed oscillator stage.

This modulated signal is fed to the base of the amplifier stage consisting of the BD139 transistor via a bocking 33nF capacitor.

The BD139 picks up the signals and matches it up with the tuned network across its collector terminals formed by the two inductors and a couple of capacitive trimmers.

These trimmers must be adjusted precisely so that the input modulated signal is optimally amplified by this stage and results in a maximum transmission output.

The output is terminated through another inductor which removes unwanted harmonics and feeds a clean amplified RF modulated signal over the connected antenna.

Antenna Specifications

The antenna should be a Yagi antenna as used for old TV sets.

The circuit must be attached very close to the antenna, preferably directly with the connecting points of the antenna.

The power supply can be fed from an external source, or a battery may be used for the same.

All the "earth" symbols must be joined together and terminated over a large copper base positioned right under the PCB...this need be done if a designed PCB is not used.

With a well designed PCB, the "earth" points must be terminated with the inbound large copper tracks which should cover the entire area of the PCB running beside the connecting tracks all across the board.

How to Set the presets

The two 10k pot may be used for optimizing the signal strength or the volume of the fed signal which is to be transmitted.

The BD139 will require a large heatsink attached with its tab.

All the coils used for this 1.5 watt transmitter circuit are 0.6mm super enamelled copper wire wound over an air core having a diameter of 5mm.

You'll also like:

  • 1.  Solar Cellphone Charger Circuit
  • 2.  3-Digit LED Capacitance Meter Circuit
  • 3.  Simple FM Radio Circuit Using a Single Transistor
  • 4.  Digital Voltmeter Circuit Using IC L7107
  • 5.  Make this Wireless Speaker Circuit
  • 6.  What’s Inside a Bluetooth Headset

About Swagatam

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials.
If you have any circuit related query, you may interact through comments, I'll be most happy to help!

Have Questions? Please Comment below to Solve your Queries! Comments must be Related to the above Topic!!

Subscribe
Notify of
16 Comments
Newest
Oldest
Inline Feedbacks
View all comments

Primary Sidebar

Calculators

  • 3-Phase Power (15)
  • 324 IC Circuits (19)
  • 4017 IC Circuits (52)
  • 4060 IC Circuits (25)
  • 555 IC Circuits (98)
  • 741 IC Circuits (19)
  • Arduino Engineering Projects (83)
  • Audio and Amplifier Projects (114)
  • Battery Chargers (82)
  • Car and Motorcycle (94)
  • Datasheets (46)
  • Decorative Lighting (Diwali, Christmas) (33)
  • Electronic Components (100)
  • Electronic Devices and Circuit Theory (36)
  • Electronics Tutorial (116)
  • Fish Aquarium (5)
  • Free Energy (34)
  • Fun Projects (13)
  • GSM Projects (9)
  • Health Related (20)
  • Heater Controllers (29)
  • Home Electrical Circuits (102)
  • How to Articles (20)
  • Incubator Related (6)
  • Industrial Electronics (28)
  • Infrared (IR) (40)
  • Inverter Circuits (98)
  • Laser Projects (12)
  • LED and Light Effect (93)
  • LM317/LM338 (21)
  • LM3915 IC (25)
  • Meters and Testers (65)
  • Mini Projects (148)
  • Motor Controller (67)
  • MPPT (7)
  • Oscillator Circuits (26)
  • PIR (Passive Infrared) (8)
  • Power Electronics (34)
  • Power Supply Circuits (77)
  • Radio Circuits (10)
  • Remote Control (48)
  • Security and Alarm (61)
  • Sensors and Detectors (120)
  • SG3525 IC (5)
  • Simple Circuits (75)
  • SMPS (29)
  • Solar Controllers (60)
  • Timer and Delay Relay (53)
  • TL494 IC (5)
  • Transformerless Power Supply (8)
  • Transmitter Circuits (40)
  • Ultrasonic Projects (16)
  • Water Level Controller (45)

Calculators

  • AWG to Millimeter Converter
  • Battery Back up Time Calculator
  • Capacitance Reactance Calculator
  • IC 555 Astable Calculator
  • IC 555 Monostable Calculator
  • Inductance Calculator
  • LC Resonance Calculator
  • LM317, LM338, LM396 Calculator
  • Ohm’s Law Calculator
  • Phase Angle Phase Shift Calculator
  • Power Factor (PF) Calculator
  • Reactance Calculator
  • Small Signal Transistor(BJT) and Diode Quick Datasheet
  • Transistor Astable Calculator
  • Transistor base Resistor Calculator
  • Voltage Divider Calculator
  • Wire Current Calculator
  • Zener Diode Calculator

© 2023 · Swagatam Innovations

wpDiscuz