RF Modules are low band radio frequency communication circuits that are used for transmission of digital data over small distances. Hence these modules are quite useful in making consumer electronics products or DIY projects for home or office environment. The 434 MHz RF module is a standard RF transmission product that is extremely popular and extensively used by hobbyists and the product engineers. Learn fundamental details about the RF communication and the basic setup of RF transmitter and receiver.
These standard 434 MHz RF modules have a data rate of 1Kbps to 10Kbps. They can operate over a distance of 50 to 80 meters without any antenna. Therefore, they are suitable to use in a small home or office culture. But, this range of operation might seem to be limited even for some home-based or office-based applications. So can the range of operation of these RF modules be extended? Yes, it is possible to increase the range of operation of the RF module twice or thrice by using an external antenna with the module.
Fig. 1: Prototype of RF Transmitter
An antenna is basically a transducer and a conductor of current which converts input electrical current into electromagnetic waves or produce electrical current in response to an electromagnetic wave. Though any conductor of electricity can be used as an antenna, there are many types of antennas and their functionality as transmitter or receiver of electromagnetic waves is governed by well established theories.
The distance to which an antenna can transmit or receive signal from, 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 to greater distance before fading away. Another method is to use standard height of the antenna as formulated by established antenna theory. Using the standard height of the antenna depending upon the frequency of the carrier wave can increase the range of operation up to two or three times. According to the antenna theory, the height of the antenna should be half or quarter of the wavelength of the carrier signal.
This project is a demonstration of the range extension of the RF module by attaching an antenna of standard size to the RF Module. The power input to the antenna has been kept constant to experience the sole effect of antenna height on the operational range of the module.
|Sr. No.||Name of component||Required qty|
|1||RF Tx Module (434 Mhz)||1|
|2||RF Rx Module (434 Mhz)||1|
|6||Resistor – 1KΩ (Quarter watt)||8|
|7||Resistor – 1MΩ (Quarter watt)||1|
|8||Resistor – 50KΩ (Quarter watt)||1|
Fig. 2: Block Diagram of RF Transmitter and Receiver
The circuit connections of the RF Module are made as in specified by the datasheets of HT12E IC, HT12D IC, RF transmitter and RF receiver. These circuit connections are explained in details in Basic Model of RF transmitter and receiver experiment. To test the effect of antenna on operational range of the RF module, first the operational range without antenna is observed. The circuit connections are made and the circuits are supplied power through a battery or portable power supply units. The circuits are taken to an open place where the straight distance between the receiver and the transmitter can be measured using a measuring tape. The address bits of both encoder and decoder ICs are hard-wired to ground to match to an address of 0x00.
Fig. 3: Prototype of RF Receiver
The data bits at the encoder IC are also hard-wired through switches to transmit a variable 4-bit data. This data bit can be set anywhere between 0x1 to 0xF so that at least one LED on the receiver module glows to indicate that the signal is properly receiving. The pin 14 of the encoder IC is hard-wired to ground to facilitate uninterrupted transmission. The push-to-on switches are used on the data pins of the encoder IC so that the transmitting bit can be changed on increasing distance.
This is important because the data pins at the decoder IC are of 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 on the decoder IC remains persistent even if the receiver module stops receiving the radio signal. So to ensure that the radio signal is receiving, the data bit has to be changed every time the distance between the transmitter and receiver is increased.
The power supply to both parts of the module is kept constant to 9V for all readings. An antenna of standard size is attached to each of the transmitter and receiver. During second phase of experiment, in the RF transmitter antenna is connected to the pin 4 of transmitter module, while, and in RF receiver antenna is connected to the pin 8 of the receiver module.
How the Circuit Works
First the operational range of the RF module is tested without antenna. The transmitter and receiver are kept at a distance of 10 metre and a change in transmitting bit is done to test the reception of radio signal at the receiver module. The bit is successfully changed. The distance between the RF transmitter and receiver is increased by 10 metre every time and the reception of radio signal is tested by changing the data bit on the transmitter module. The 434 RF modules successfully receive signals over a distance between 70 to 80 metre. Beyond 80 metre, the radio signal is faded away and the change in transmitted bit is not reflected on the receiver module. Thus, the operational range of 434 RF modules without antenna can be safely predicted to be 70 metre.
Now, the operational range of the module with antenna is tested. Before that the standard height of the antenna has to be calculated. The standard height according to the antenna theory should be half or one-fourth 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 follow – :
Time period = 1/Frequency
= 2.4 Nano-seconds
The speed of light is 3X10^8 m/sec. The wavelength of the radio waves is given by the following – :
Wavelength = Speed/Frequency
= Speed X Time Period
= .69 metre or 69 cm
The standard size of antenna should be half or quarter of the wavelength.
Size of Antenna = 69/2 or 69/4
= 34.5 or 17.25 cm
The quarter of the wavelength is taken as the standard size of the antenna in this project. A wire is cut to lengths of 17.25 cm and connected to each, the RF transmitter and the receiver module.
Now, the operational range of RF module is tested in increments of 10 metre as done without antenna. Now the RF module is found to be transmitting signal over a distance between 150 and 160 metres. The new operational range is precisely measured to be 156 metre by changing the increment to 1 metre beyond 150 metre distance. Hence, on attaching an antenna of quarter length of the wavelength, the operational range of the RF module is just doubled.
|Without Antenna||With Antenna|