RF modules are widely used by electronics enthusiasts. They are also used in a large number of consumer electronics products. These modules are used for wireless data transmission and for implementing remote control systems. The 434 MHz RF module is the most commonly used module available on the market. These modules are capable of transmitting 4-bit data at once at a data rate of 1 Kbps to 10 Kbps. Learn about RF transmission and the basic configuration of RF transmitter and receiver modules.
The typical operating range of 434 MHz RF modules is between 50 meters and 80 meters. The operating range of the RF module can be greatly increased by connecting external antennas to the RF transmitter and receiver. Learn about the unique effect of connecting a standard size antenna on the RF module's operating range.
The range of the RF module can be further increased by increasing the transmit power of the antennas. This project is a demonstration of increasing the operational range of the RF module by increasing the transmit power after the standard size antennas, as per antenna theory, are already connected to the transmitter and receiver sections.
Required components
| Mr. No. | Component Name | Necessary amount. |
|---|---|---|
| 1 | RF Tx Module (434 MHz) | 1 |
| two | RF Rx Module (434 MHz) | 1 |
| 3 | HT12E | 1 |
| 4 | HT12D | 1 |
| 5 | LED | 5 |
| 6 | Resistor – 1KΩ (a quarter of a watt) | 8 |
| 7 | Resistor – 1MΩ (a quarter of a watt) | 1 |
| 8 | Resistor – 50KΩ (a quarter of a watt) | 1 |
| 9 | push button | 4 |
| 10 | Battery – 9V | 4 |
| 11 | Bread Board | two |
| 12 | Connecting wires | – |
Fig. 1: Block diagram of RF transmitter and receiver
Circuit Connections
Circuit connections are made as specified in the data sheets for the RF module and encoder and decoder ICs. The 17.25 cm tall antennas are connected to the receiver and transmitter sections in addition to the basic configuration. Both the HT12E encoder and the HT12D decoder IC are wired to have address 0x00. Pin 14 of the encoder IC is grounded to allow uninterrupted signal transmission. Push-to-on switches are used on the data pins of the IC encoder to change the data bits in the range of 0x1 to 0xF on each read.
In the receiver section, LEDs are connected to the data pins of the decoder IC to get a visual cue of the change in transmitted and received data bits. The LEDs are connected between the data pins and ground with 1K ohm pull-up resistors in series. This circuit configuration allows the LEDs to turn on when receiving a HIGH bit while turning off when receiving a LOW bit.
Fig. 2: RF Transmitter Prototype
The 17.25 cm tall antennas are connected to pin 4 of the RF transmitter in the transmitter section and to pin 8 of the RF receiver in the receiver section. The circuits are powered by 9V batteries. In the first and second phases of the experiment, individual 9V batteries are used to power the circuits. In the third phase of the experiment, two 9V batteries are connected in parallel to supply power to both circuits. In the fourth and final phase of the experiment, two 9V batteries are connected in series to supply power to both circuits.
The antennas are single wires cut into 17.25 cm lengths, which is one-fourth the wavelength of the 434 MHz RF module carrier wave.
How the circuit works
The experiment is carried out in four phases. First, the range of the RF module is tested without an antenna. The module is taken to an open location where the straight distance between the transmitter and receiver can be measured using a tape. The distance between the transmitter and the receiver is kept at 10 meters and the data bit is changed to test the signal reception in the receiver section. The distance is increased by 10 meters in each subsequent test and the test is stopped when no change in the data bit is reflected in the receiving section after a certain distance. In the first phase, when the RF module is used without an antenna, the operating range of the RF module is 68 meters.
In the second phase, antennas of standard height, i.e. 17.25 cm, are connected to the transmitter and receiver sections and both sections are powered by individual 9V batteries. The range of the RF module is again tested by increasing the distance between the transmitter and receiver in 10 meter increments and further to an accurate reading in 1 meter increments and then changing the data bit for testing at each step. In the second phase, when external antennas are connected and power transmission is kept constant at 9V, the extended operating range of the RF module is 150 meters.
Fig. 3: RF receiver prototype
In the third phase, the power supply for the transmitter and receiver circuits is replaced by two 9V batteries connected in parallel to each section. When connecting batteries in parallel, the current supplied to the circuit and antennas increases, but the supply voltage drops by half, to 4.5V. Due to the reduction in supply voltage, power transmission to the circuits and antennas is reduced and the operating range of the RF module is also reduced. In the third phase, when batteries connected in parallel supply power to the transmitter and receiver sections, the operational range of the module is 100 meters.
In the fourth phase, the transmitter and receiver sections are powered by two 9V batteries connected in series each. Connecting the batteries in series maintains the same current supplied to the circuits and antennas, but doubles the supply voltage to 18V. Due to the increase in supply voltage, the power transmission to the antennas increases and the operational range of the RF module also increases. In the fourth and final phase of the experiment, when batteries connected in series power both sections, the operating range of the RF module is increased to 300 meters.
| The. | Constant power supply without antenna (9V) | 68 meters |
| B. | Constant power supply with antenna (9V + antenna) | 150m |
| w. | Variable power supply without antenna (two 9V batteries in parallel) | 100m |
| d. | Variable Power Supply with Antenna (Two 9V Batteries in parallel + Antenna) | 300m |
The experiment shows that power transmission to the antennas can be increased by increasing the supply voltage. The operating range of the RF module is directly proportional to the power transmission. It can be doubled by doubling the supply voltage.
Circuit diagrams
| Circuit Diagram-RF-Transmitter-Receiver-Increased Range-Antenna-Higher-Transmission Power |  |