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RF
design guide What
is a radio module?
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What is a radio module?
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All users want products that they
can use easily, that offer good performance and that are low priced.
In other words, they would like to buy radio equipment at low cost,
that can be used without a radio operator license, with simple,
error-free operation over a wide communication range.
There are surely very few such perfect products, and trying to create such ideal equipment
is a perpetual problem for manufacturers.
Among these
products that do
not require a radio operator license are mobile
phones and wireless LANs, a whole range of wireless data
communications equipment, wireless security equipment and so on. These
kinds of devices are used very widely in industrial and consumer
fields.
Radio
modules make up the portion of this sort of radio equipment that uses
high frequencies.
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Why are radio modules necessary?
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It
is often said that high
frequency circuits do
not perform as well as they should in theory, and cannot
be made without experience. For this reason, for engineers who are
entering the field of electrical circuit design from the design of
audio equipment or logic, the threshold may seem rather high and is
one reason why they hesitate to become involved. In addition there is
the issue of legal regulations, and it can all seem rather a hassle.
Of course this is not actually the case, but any design that is
started from scratch is naturally going to be very difficult. It is
from this background that the requirement arises for just a high
frequency element that can be built into equipment as a component
(module). As the difficulty of designing the high frequency element
and ensuring performance is taken care of, and there
is
peace of mind concerning the legal procedures, equipment designers can
concentrate on the design of the other elements, and so they very much
appreciate radio modules.
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What
type of modules are there?
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following is an introduction, according to their features, to the
types of modules available. |
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By
type of module
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The
types of radio modules include transmitters
that only transmit signals, receivers that only receive signals, and
transceivers incorporating functions for transmitting and receiving. A
combination of transmitter and receiver is used for one-way
communication. Transceivers are used for duplex communication.
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By
frequency band
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1)
434 MHz band
434
MHz band radio modules transmit information data in a narrow band
frequency and effectively utilize the radio waves. The characteristic of
radio waves in the 434 MHz band is their comparatively wide operating
range.
2)
868 MHz band
Similarly
to the 434 MHz band, these modules transmit using
narrow band modulation. Compared with the 434 MHz band, there is not
very much of this equipment in use, so there are advantages from the
point of view of less radio interference. Their
operating range is somewhat
narrower.
3)
2.4 GHz band
Spread
spectrum communication systems are authorized
for use in 2.4
GHz low power data communication systems, and radio modules with systems
that spread information data across a
wide band are .
2.4 GHz radio waves have high straightness, and compared to 400 MHz, the
radio waves have less diffraction and are inferior from the point of
view of communication range. But because of the high bit rate and
excellent security of spread spectrum communication, and its good noise
immunity, the number of manufacturers using it are increasing, and the
field is very congested.
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By
digital modulation system
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The
modulation systems used in these modules are FSK (CPFSK, MSK, GMSK), PSK
(BPSK, QPSK, DQPSK), and ASK.
In general, ASK is easily affected by environmental conditions, and is
used in micro-power radio equipment for short range communication over a
few meters.
FSK
and PSK are used for their reliability and communication range. FSK is
comparatively low cost, small size, with low power consumption and a low
error rate. PSK circuits are rather complex, but are used widely. The
occupied frequency band of MSK and GMSK is narrow while the operating
range is wide. DQPSK uses multi-level modulation and has a relatively
narrow occupied bandwidth. With a high bit rate and few errors, it is
used widely.
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By
frequency channel used
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With
the frequency used fixed at one wave and using a synthesizer system,
many frequency channels are supported. In general, radio modules using
one wave are small with low power consumption, and achieve excellent
cost performance.
With modules using a
synthesizer system you can switch to another channel for communication
if the result of carrier sensing indicates that a particular frequency
channel is being used.
There
are also modules with a built in function that can switch channels
automatically.
Depending
on the frequency channel used, there may be limits on methods of usage
such as transmission time limits and the like. |
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By
type of oscillation circuit
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There
are two types of oscillation circuit, crystal and SAW resonator types.
The crystal type has excellent frequency stability while the SAW
resonator type is slightly inferior with regard to frequency stability,
but this
type is
often
used for its lower cost.
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By
data input/output method
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There
are two formats for inputting data in radio modules, serial data input
and parallel data input. Available code formats for serial data include
NRZ code, NRZI code, DMI code, Manchester code and so on. However, as
occupied frequency band and bit rate have an involved relationship with
the code format, it is necessary to check carefully which coding can be
handled.
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By
data transmission rate (bit rate)
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Data
rates range widely from several hundred bps to tens of Mbps. The bit
rate for telecontrol can be 2,400 bps, 4,800 bps and so on, and for data
transmission there are radio modules with rates in the tens of Mbps and
high speed modules.
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By
data processing method
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Dedicated
telecontrol radio modules and radio modules for data transmission must
transmit simple command data and data streams.
However
there are modules that come
with
error processing protocols and data link processing protocols, and those
that do not have special protocols. The former simply requires you to
input data using the module's data input terminal, and the module
processes it for you, whereas the latter requires the designer to give
the module a proprietary transmission protocol.
There
are also individual modules that can be used in either way.
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By
legal procedure
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If
you have a radio module that conforms to a standard specification, you
can avoid the complex bureaucratic procedures required for
authorization, and significantly reduce the time required for
commercialization.
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By
application
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Modules
that use batteries must be small sized and have low power consumption.
With
modules for industrial use, it is necessary to pay attention to factors
in the operating environment such as working temperature, humidity and
the like.
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