Radio Communication
Wireless uses a radio wave within the electromagnetic spectrum to convey (carry) information. It's called a "carrier wave" or simply "carrier". Unpacking that first sentence is a challenge but definition of some terminology is necessary before discussing radio communication. Information can be audio (conversation or music, for example), or it can be digital (a sequence of "1"s and "0"s, or ON and OFF), which works well for remote control.
The Electromagnetic Spectrum
Radio communication uses a small portion of the electromagnetic spectrum which is everywhere. Without it there's no light; no anything. This is a nice diagram, courtesy of NASA, which I've edited for this document.
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It's not necessary to understand radio technology to use radio communication. Just buy the right components and put them together. Problem is, there are hundreds of components from which a few must be selected to implement remote control. S-CAB components, battery power supply, radio transmission and decoders are designed to work together. What follows is a bit of why and how. It can be skipped by those who have already decided to use S-CAB components and do not plan to venture into unknown territory.
TerminologyThe electromagnetic spectrum diagram above introduces two important parameters:
To transmit information one or more carrier wave properties, such as amplitude or frequency, are modified by an information bearing signal, called the message signal. The process is called "modulation"
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ISM BandsISM radio bands, which are defined by frequency, are portions of the radio spectrum reserved for industrial, scientific and medical purposes. Applications for model train control use the following ISM bands:
Radio interferenceDevices in close proximity transmitting simultaneously at the same frequency will interfere and communication will fail. ISM bands are unlicensed and therefore available to any user so long as they comply with government regulations. Since there are many users and no coordination of frequency allocation within an ISM band, interference is an expected risk, especially in the 900 MHz band.
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Radio communication technologiesWiFi is a wireless data networking technology to provide internet access and connect devices like computers and smartphones to a network. Compliance with industry standards is required to ensure interoperability.
Bluetooth is a wireless technology that allows short-range communication between devices like smartphones, headphones, and keyboards without cables. Compliance with industry standards is required to ensure interoperability.
The 900 MHz band is used for remote sensing and control in
low-power consumer electronics, security systems, industrial and agricultural sensors, etc. There are no international standards but applications must be certified to comply with regional regulations. |
Choice of radio technologyWiFi
Products have been developed for loco control using ESP8266 WiFi modules. Quoting Internet documentation.
The ESP8266 is a fully capable microcontroller with built-in Wi-Fi capabilities, offering a complete and self-contained Wi-Fi networking solution. Is WiFi overkill train control? Model locos don't communicate with each other. They receive commands from a controller. A network is not required. Problem is, an ESP8266 module requires 250 mA from a 3.3 volt power supply which is serious consumption of battery energy for unused WiFi capability. Why not choose something simpler that consumes less energy?
Bluetooth
BLE (Bluetooth Low Energy) is a good option for battery powered use. Peak current in an active state is 10 to 30 mA. Its the best choice if using a mobile phone or tablet PC for loco control. At present, product choice is limited.
900 MHzThis is the simplest technology and was first applied in model railroading by suppliers for DCC wireless throttles.
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