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Transmission solutions essentially send information from one place to another via radio waves. This is a type of wireless communication – so-called because, of course, it doesn’t require physical wires. Other types of common radio transmission include radio and television broadcasting and walkie-talkies.
There are two essential components in any radio transmission solution: a transmitter and a receiver. The transmitter is the component which generates and sends the signal, while the receiver is the component which picks up the signal and displays or utilises the information contained within it.
Radio waves are a type of electro-magnetic waves. They are invisible and cannot be detected by humans in any way. The spectrum of radio waves is split into a vast quantity of different frequencies. In the early days of radio transmission, transmitters sent static messages which spanned the entire spectrum of frequencies. Today, because there are thousands of radio waves around us all the time being used for hundreds of different purposes, transmitters use continuous sine waves to send information.
The transmitter takes the data in the message, encodes it onto a sine wave, and transmits it to its destination via radio waves.
The receiver picks up the radio waves and decodes the same message from the sine wave.
The message to be transmitted can take many forms – a basic string of text, a recording of someone’s voice, still or video images. It can all be encoded onto sine waves and sent wirelessly through the air. The process of encoding the information onto the waves is called modulation.
There are three primary methods of modulating sine waves:
The frequency of a sine wave is how quickly or slowly the wave oscillates from top to bottom in one complete cycle. It is measured in cycles per second. This measure is also known as hertz.
The place you are most likely to have come across frequency measures is on a radio. The numbers that identify the channel you are listening to (for example, BBC Radio 1 is 97-99 FM) refer to the frequency band over which those channels transmit. Tuning your radio to 99 FM means that the radio transmitter is generating a sine wave at 99,000,000 hertz (cycles per second).
In access control, radio transmission is commonly used for wireless activation of security systems. Let’s look at an example of an automated car gate at the end of a driveway. The gate is fitted with an electro-magnetic lock at its centre.
Hidden in a control panel at the side of the gate is the receiver. The resident of the house, who is driving up towards the gate, has a hand-held transmitter in their car. If they are in range of the receiver, when they press the button on the transmitter, it generates a signal and sends it to the receiver. The receiver recognises the signal and in turn, triggers the lock to release and the gate to automatically open.
Transmission solutions are also common for automatic garage door openers, wireless access control keypads, and automatic light switches.
In its basic form, radio transmission is not very secure. Devices exist which can interrupt the signal mid-transmission and allow hackers to gain access to the information being sent. However, there are now multiple methods for encrypting the information to ensure that it cannot be stolen.
One of those methods is KeeLoq® rolling code. This method is intended to prevent hackers from intercepting signals used in access control systems. By constantly changing the ‘password’ required to gain access (on a rolling basis), even if it is intercepted, by the time the hacker tries to use the password they have stolen, it has already changed.
There are several key features that distinguish different types of radio receivers and whether they are suitable for different projects.
|Number of relays||A relay is a switch that opens or closes a circuit. In transmission, when a valid transmission signal is picked up by the receiver, it triggers a relay to change from open to closed or from closed to open. This change in state in the circuit is what controls the action – a light turning on, a door unlocking, or a gate automatically opening. If a receiver is equipped with more than one relay, it can control more than one circuit.|
|Memory capacity||This refers to the number of different transmitters that the receiver has space to accommodate.|
|Modulation type||Modulation is the process of encoding the message into the sine wave that is transmitted. Demodulation is the reverse: separating out the original message from the transmitted sine wave. Common methods are AM and ASK. As long as both the transmitter and receiver use the same type, the message will be successfully transmitted.|
|Frequency||The frequency of the transmitter must be the same as the frequency of the receiver. This ensures that the sine waves are being sent to and from the intended components. Most CDVI transmission solutions run at 433.92MHz.|
|Encoding method||Encoding is the process of converting data into a binary signal. Some methods offer additional security benefits, such as KeeLoq® hopping code, which constantly changes the valid passcode to prevent interception.|
|Power supply||Transmitters and receivers require a power supply to function. This might be a wired power supply or a battery. It is important to ensure you have the right version of the product with a power requirement that matches the rest of your system.|
|IP rating||If your components are to be installed outdoors or exposed to the elements, you should look for IP ratings. These measure the product’s resistance to the ingress of solids and liquids that might affect performance. The highest possible IP rating is IP68.|