An RF module is a small electronic device used to transmit and/or receive
radio signals between two devices. In an embedded system it is often desirable to
communicate with another device wirelessly. This wireless communication
may be accomplished through optical communication or through radio frequency
communication. For many applications the medium of choice is RF since it does not
require line of sight. RF communications incorporate a transmitter and/or
receiver. 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. In addition, reliable RF
communication circuit requires careful monitoring of the manufacturing process
to ensure that the RF performance is not adversely affected. Finally, radio
circuits are usually subject to limits on radiated emissions, and require
Conformance testing and certification by a standardization organization such as
ETSI or the U.S. Federal Communications Commission. For these reasons, design
engineers will often design a circuit for an application which requires radio
communication and then "drop in" a pre-made 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 those in the
industrial, scientific and medical radio bands such as 433.92 MHz, 915 MHz, and
2400 MHz. These frequencies are used because of national and international
regulations governing the used of radio for communication. Short Range Devices
may also use frequencies available for unlicensed such as 315 MHz and 868 MHz.
RF modules may comply with a defined protocol for RF communications such as
Zigbee, Bluetooth low energy, or Wi-Fi, or they may implement a proprietary
protocol. 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. RF modules typically
incorporate a printed circuit board, transmit or receive circuit, antenna,
and serial interface for communication to the host processor.
Most standard, well known types are covered here:
Transmitter module Receiver module
Transceiver module System on a chip 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. RF
transmitters are usually subject to regulatory requirements which dictate
the maximum allowable transmitter power output, harmonics, and band edge
requirements. = Receiver modules =
An RF receiver module receives the modulated RF signal, and demodulates it.
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. = Transceiver modules =
An RF transceiver module incorporates both a transmitter and receiver. The
circuit is typically designed for half-duplex operation, although
full-duplex modules are available, typically at a higher cost due to the
added = System on a chip module =
An SoC module is the same as a transceiver module, but it is often made
with an onboard microcontroller. The microcontroller is typically used to
handle radio data packetisation or managing a protocol such as an IEEE
802.15.4 compliant module. This type of module is typically used for designs
that require additional processing for compliance with a protocol when the
designer does not wish to incorporate this processing into the host
microcontroller. Host microcontroller interface
RF modules typically communicate with an embedded system, such as a
microcontroller or a microprocessor. The communication protocols include UART,
used in Digi International's X-Bee modules, Serial_Peripheral_Interface_Bus
used in Anaren's AIR modules and Universal Serial Bus used in Roving
Networks' modules. Although the module may use a standardized protocol for
wireless communication, the commands sent over the microcontroller interface
are typically not standardized as each vendor has its own proprietary
communications format. The speed of the microcontroller interface depends on the
speed of the underlying RF protocol used: higher speed RF protocols such as
Wi-Fi require a high-speed serial interface such as USB whereas protocols
with a slower data rate such as Bluetooth Low Energy may use a UART
interface. RF signal modulation
There are three types of signal modulation methods commonly used in RF
transmitter and receiver modules: ASK
OOK FSK
Direct-sequence spread spectrum Frequency-hopping spread spectrum
The detailed description, advantages and disadvantages are listed in the linked
articles above. Main factors affecting RF module
performance As with any other RF 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, dense construction to
absorb the radio wave signals, so the effective operational distance will in
most practical instances be less than specified.
Module Physical Connection A variety of methods are used to attach
an RF module to a printed circuit board, either with through-hole technology or
surface-mount technology. Through-hole technology allows the module to be
inserted or removed without soldering. Surface-mount technology allows the
module to be attached to the PCB without an additional assembly step.
Surface-mount connections used in RF modules include land grid array and
Castellated Holes. The LGA package allows for small module sizes as the
pads are all beneath the module but connections must be X-rayed to verify
connectivity. Castellated Holes enable optical inspection of the connection but
will make the module footprint physically larger to accommodate the
pads. Wireless protocols used in RF modules
RF modules, especially SoC modules, are frequently used to communicate according
to a pre-defined wireless standard, including:
S-WAVE Smart Wave Zigbee
Bluetooth low energy Wi-Fi
IEEE 802.15.4 Z wave
However, RF modules are also frequently used in proprietary protocols, such as a
garage door opener. 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 References
External links F. Egan, William. Practical RF System
Design. Wiley-IEEE Press. ISBN 978-0-471-20023-9.
Fairall, John. An Introduction to low power radio. RF Solutions Ltd. ISBN
978-0-9537231-0-2. RF Modul Mühendislilk Tasarımlarıyla
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