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  3. RF design guide
  4. What is a radio module?

RF Technical Resources

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  • Modem evaluation

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.

What type of modules are there?

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The following is an introduction, according to their features, to the types of modules available.

By type of module
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.
By frequency band
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 available in the market. 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.
By digital modulation system
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.
FFSK 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.
By frequency channel used
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.
By type of oscillation circuit
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.
By data input/output method
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.
By data transmission rate (bit rate)
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.
By data processing method
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.
By legal procedure
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.
By application
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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