Here is the simple and easy DIY tutorial on FM telephone transmitters, which is going to demonstrate in detail. The FM telephone transmitter circuit is built on a PC board that is portable and can easily be fitted inside the telephone housing which makes it an instant pseudo-speak earphone. Although, this FM transmitter circuit connects in series with the telephone line. The circuit gets power from the main telephone line and transmits both sides of the conversation to an FM radio tuned between 90 and 95 MHz
Furthermore, the circuit schematic shown below is a layout of a simple FM telephone transmitter. Generally, the FM telephone transmitter will transmit the telephone conversation to any FM receiver to a small distance of only 180 feet.
Hardware Components
The following components are required to make FM Telephone Transmitter Circuit
| S.no | Component | Value | Qty |
|---|---|---|---|
| 1. | Transistor | 2SA933 | 1 |
| 2. | Silicon diode | 1SS119 | 4 |
| 3. | Inductor | 8 turns | 1 |
| 4. | Antenna | – | 1 |
| 5. | LED | – | 1 |
| 6. | Capacitor | 330pF, 470pF, 12pF, 24pF | 1, 1, 1, 1 |
| 10. | Resistor | 12k, 1k, 200 ohms | 1, 1, 1 |
2SA933 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of 2SA933
FM Telephone Transmitter Circuit
Working Explanation
The circuit incorporates an “On Air” LED indicator and furthermore gives a switch that utilizes to switch off the transmitter. One of the amazing features of the circuit is that no battery is utilized to operate the circuit since power is taken from the telephone line directly.
The transmitter utilizes just a short wire of around 4″/10 cm long to transmit the signal. However, a small portion of the RF signal is likewise emanated through the phone line itself. The circuit may be utilized to share or record telephone conversations. However, it isn’t expected for illicit use. Q1 is a 2SA933 Transistor that is used to amplify the signal. The diode D1 to D4 is a 1SS119 silicon diode that makes a bridge. And L1 is equivalent to 8 turns of 23-check enameled wire twisted on a 3.6mm distance across the structure.
Applications and Uses
- It utilizes to transmit telephone conversations over a range of 180 feet.
