RF modules are low-band radio frequency communication circuits used for transmitting digital data over short distances. Hence, these modules are quite useful in manufacturing consumer electronics or DIY projects for home or office environments. The 434 MHz RF module is an extremely popular standard RF transmission product widely used by hobbyists and product engineers. Learn fundamental details about RF communication and basic RF transmitter and receiver configuration.
These standard 434 MHz RF modules have a data rate of 1 Kbps to 10 Kbps. They can operate at a distance of 50 to 80 meters without any antenna. Therefore, they are suitable for use in a small home or office. But, this range of operation may seem limited even for some home or office applications. So can the operating range of these RF modules be extended? Yes, it is possible to increase the operating range of the RF module two or three times by using an external antenna with the module.
Fig. 1: RF Transmitter Prototype
An antenna is basically a transducer and a current conductor that converts incoming electrical current into electromagnetic waves or produces electrical current in response to an electromagnetic wave. Although any conductor of electricity can be used as an antenna, there are many types of antennas and their functionality as a transmitter or receiver of electromagnetic waves is governed by well-established theories.
The distance to which an antenna can transmit or receive a signal can be increased by increasing the power applied to the antenna. This technique increases the strength of the carrier wave and the radio signal becomes capable of transmitting greater distances before disappearing. Another method is to use the standard antenna height as formulated by established antenna theory. Using the standard antenna height depending on the carrier wave frequency can increase the operating range by up to two or three times. According to antenna theory, the height of the antenna should be half or a quarter of the wavelength of the carrier signal.
This project is a demonstration of extending the range of the RF Module by attaching a standard size antenna to the RF Module. The power input to the antenna was kept constant to experience the unique effect of antenna height on the module's operational range.
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 | two |
| 11 | Bread board | two |
| 12 | Connecting wires | – |
Fig. 2: Block diagram of RF transmitter and receiver
Circuit Connections
RF Module circuit connections are made as specified in the data sheets of the HT12E IC, HT12D IC, RF transmitter and RF receiver. These circuit connections are explained in detail in the Basic RF Transmitter and Receiver Experiment Model. To test the effect of the antenna on the operational range of the RF module, the operational range without antenna is first observed. Circuit connections are made and the circuits receive power through a battery or portable power supplies. The circuits are taken to an open location where the straight distance between the receiver and transmitter can be measured with a tape measure. The address bits of the encoder and decoder ICs are connected to ground to correspond to an address of 0x00.
Fig. 3: RF receiver prototype
The data bits in the encoder IC are also connected through switches to transmit 4-bit variable data. This data bit can be set anywhere between 0x1 and 0xF so that at least one LED on the receiver module lights up to indicate that the signal is being received correctly. Pin 14 of the encoder IC is connected to ground to facilitate uninterrupted transmission. Push-to-on switches are used on the data pins of the encoder IC so that the transmission bit can be changed with increasing distance.
This is important because the data pins on the decoder IC are latch type and the data bit transmitted once remains on the data pins of the decoder IC until a new bit is received. Therefore, a data bit, once received at the decoder IC, remains persistent even if the receiving module stops receiving the radio signal. Therefore, to ensure that the radio signal is being received, the data bit must be changed every time the distance between the transmitter and receiver increases.
The power supply for both parts of the module is kept constant at 9V for all readings. A standard size antenna is attached to each transmitter and receiver. During the second phase of the experiment, in the RF transmitter the antenna is connected to pin 4 of the transmitter module, while in the RF receiver the antenna is connected to pin 8 of the receiver module.
How the circuit works
First, the operating range of the RF module is tested without an antenna. The transmitter and receiver are kept at a distance of 10 meters and a change in the transmit bit is made to test the reception of the radio signal at the receiver module. The bit has been changed successfully. The distance between the RF transmitter and the receiver is increased by 10 meters each time and the reception of the radio signal is tested by changing the data bit in the transmitter module. RF 434 modules successfully receive signals at a distance of between 70 and 80 meters. Beyond 80 meters, the radio signal disappears and the change in the transmitted bit is not reflected in the receiving module. Thus, the operational range of 434 RF modules without antenna can be safely predicted to be 70 meters.
The operational range of the module with antenna is now tested. Before this, the standard antenna height must be calculated. The standard height according to antenna theory should be half or a quarter of the wavelength of the carrier signal. The carrier frequency of the RF module is 434 MHz.
The time period of the RF wave will be as follows –:
Time Period = 1/Frequency
= 1/434 MHz
= 2.4 nanoseconds
The speed of light is 3X10^8 m/s. The wavelength of radio waves is given by the following –:
Wavelength = Speed/Frequency
= Speed X Period of time
= 3X10^8X2.4X10^-9
= 0.69 meter or 69 cm
The standard antenna size should be half or quarter wavelength.
Therefore,
Antenna Size = 69/2 or 69/4
= 34.5 or 17.25 cm
The quarter wavelength is considered the standard antenna size in this design. A wire is cut into 17.25 cm lengths and connected to each RF transmitter and receiver module.
Now, the operational range of the RF module is tested in 10 meter increments, as done without an antenna. Now the RF module is transmitting signal at a distance between 150 and 160 meters. The new operational range is accurately measured at 156 meters, changing the increment to 1 meter beyond the 150 meter distance. Consequently, by connecting a quarter-wavelength antenna, the operating range of the RF module is only doubled.
| Without Antenna | With Antenna | |
|---|---|---|
| Range -> | 70m | 156m |
Circuit diagrams
| Circuit Diagram-RF-Transmitter-Receiver-Range-Increased-Antenna-Higher-Transmission-Power_0 |  |
