RF Transmitter and Receiver

 RF TRANSMITTER AND RECEIVER 

An RF module (radio frequency module) is a (usually) small electronic circuit used to transmit and/or receive radio signals on one of a number of carrier frequencies. RF modules are widely used in electronic design owing to the difficulty of designing radio circuitry. Good electronic radio design is notoriously complex because of the sensitivity of radio circuits and the accuracy of components and layouts required to achieve operation on a specific frequency. Design engineers will design a circuit for an application which requires radio communication and then "drop in" a radio module rather than attempt a discrete design, saving time and money on development.

RF modules are most often used in medium and low volume products for consumer applications such as garage door openers, wireless alarm systems, industrial remote controls, smart sensor applications, and wireless home automation systems. They are sometimes used to replace older infra red communication designs as they have the advantage of not requiring line-of-sight operation.

Several carrier frequencies are commonly used in commercially-available RF modules, including 433.92 MHz, 315 MHz, 868 MHz and 915 MHz. These frequencies are used because of national and international regulations governing the used of radio for communication. (citation needed)

TYPES OF RF MODULES:

The term RF module can be applied to many different types, shapes and sizes of small electronic sub assembly circuit board. It can also be applied to modules across a huge variation of functionality and capability. Most standard, well known types are covered here:

·         Transmitter module

·         Receiver module

·         Transceiver module

Transmitter modules

An RF transmitter module is a small PCB sub-assembly capable of transmitting a radio wave and modulating that wave to carry data. Transmitter modules are usually implemented alongside a micro controller which will provide data to the module which can be transmitted.

Intelligent transmitter module

An intelligent transmitter module is the same as a transmitter module, but it is often made with an on-board micro controller to handle radio data packetisation negating the need for an external micro controller to convert data or Manchester encode it. This type of module is usually used for designs requiring a quick route to market or if the designer has little experience designing with radio.

Super heterodyne and super-regenerative receivers:

There are two types of RF receiver modules: superheterodyne receivers and super-regenerative receivers. Super-regenerative modules are usually low cost and low power designs using a series of amplifiers to extract modulated data from a carrier wave. Super-regenerative modules are generally imprecise as their frequency of operation varies considerably with temperature and power supply voltage. Superheterodyne receivers have a performance advantage over super-regenerative; they offer increased accuracy and stability over a large voltage and temperature range. This stability comes from a fixed crystal design which in turn leads to a comparatively more expensive product.

RF signal modulation:

There are three types of signal modulation methods commonly used in RF transmitter and receiver modules:

·         ASK

·         FSK

·         OOK

The detailed description, advantages and disadvantages are listed in the linked articles above.

Main factors affecting RF module performance:

As with any other radio-frequency device, the performance of an RF module will depend on a number of factors. For example, by increasing the transmitter power, a larger communication distance will be achieved. However, this will also result in a higher electrical power drain on the transmitter device, which will cause shorter operating life for battery powered devices. Also, using a higher transmit power will make the system more prone to interference with other RF devices, and may in fact possibly cause the device to become illegal depending on the jurisdiction.

Correspondingly, increasing the receiver sensitivity will also increase the effective communication range, but will also potentially cause malfunction due to interference with other RF devices.

The performance of the overall system may be improved by using matched antennas at each end of the communication link, such as those described earlier.

Finally, the labeled remote distance of any particular system is normally measured in an open-air line of sight configuration without any interference, but often there will be obstacles such as walls, floors to absorb the radio wave signals, so the effective operational distance will in most practical instances be less than specified.

Typical applications:

·         Vehicle monitoring

·         Remote control

·         Telemetry

·         Small-range wireless network

·         Wireless meter reading

·         Access control systems

·         Wireless home security systems

·         Area paging

·         Industrial data acquisition system

·         Radio tags reading

·         RF contactless smart cards

·         Wireless data terminals

·         Wireless fire protection systems

·         Biological signal acquisition

·         Hydrological and meteorological monitoring

·         Robot remote control

·         Wireless data transmissions

·         Digital video/audio transmission

·         Digital home automation, such as remote light/switch

·         Industrial remote control, telemetry and remote sensing.

·         Alarm systems and wireless transmission for various types of low-rate digital signal.

·         Remote control for various types of household appliances and electronics projects.

·         Many other applications field related to RF wireless controlling

·         Mobile web server for elderly people monitoring