The word "Transponder" is a combination of the words "Transmitter" and "Responder"; a transponder Transmits a Response. It's an electronic translator device or an electronic converter device that responds to an incoming signal type by transmitting a different signal type.
There are lots of electronic devices that fall into the categories of electronic translator or electronic converters. Some have low power input and/or outputs, some have high power inputs and/or outputs.
Types of Transponder
Example - Aircraft Transponder - Many people think of a transponder as a device in an aircraft that, whenever the aircraft receives a radar-ping, the transponder sends an identifier, altitude information, and other information. That transmitted response allows the air traffic controller to keep better track of the aircraft's location.
Example - Satellite Transponder - A satellite is also sometimes considered to be a transponder. It receives a signal on one frequency that contains data or other information, and repeats the data or other information on another frequency. Although, the satellite transponder can sometimes also be considered to be a repeater, because often, even though it transmits on a different frequency than it received the information, it only repeats the data or other information exactly the way it received it.
Both of these are wireless input and output transponders, and there are many definitions of transponders refer to wireless input and output only. Manufacturers, on the other hand, when they market their equipment, often include other possibilities. Other possibilities include:
- Wireless in / wired out
- Wired in / wireless out
- Wired in / wired out
- Fiber optic in / wired out
- Wired in / fiber optic out
- Fiber optic in (receiving one color) / fiber optic out (transmitting another color)
- Etc.
The Word Transponder is a Broad Term
Many transponders are multi-use electronic devices; a single transponder can be used to receive signals from one or more directions and transmit a response in one or more multiple directions.
Example - An addressable fire alarm system or security system supervised input module is sometimes called a transponder. It is connected to two, three, and sometimes four input and/or output circuits.
- A conventional circuit
- A digital two-way signaling circuit (or separate digital input and digital output circuits)
- A power circuit, which can be separate from the signaling circuit, or combined with the signaling circuit
Depending on the signal or power received on one of the circuits, the module transmits a response (trans-ponds) in another circuit, or even back on the same circuit:
- It takes power in from the panel, uses some for its own use, and transmits some of it on to the conventional circuit
The output power is used to supervise the wires on the conventional circuit (making sure all devices are connected), and sometimes the power is also used by a conventional device (like a smoke detector)
- Some of them will respond to the digital signal from the signaling circuit by momentarily turning off and on again the transmitted power to the input device - a means of resetting a conventional smoke detector
- It responds to a change voltage/resistance/current on the conventional circuit by transmitting a digital response (normal - alarm - trouble) on the signaling circuit
- It responds to polling from the panel on the signal circuit (a type of supervision) by transmitting digital information back on the same signal circuit
Example: A fire alarm system or security system addressable device is really a device that has a transponder embedded into a device. In reality, the device itself is almost the same as a conventional device; the transponder, though, is just included in the package.
Example: A wireless device is a conventional fire alarm or security device with the wireless transponder built into the same package.
Example: A wireless receiver in a fire alarm or security system receives a wireless signal, and responds by converting and transmitting that original wireless signal onto a wired digital circuit.
A Transponder is what a Manufacturer Says is a Transponder
Some manufactures say that an addressable input or output device is a fire alarm or security system module; some manufacturers say that an addressable input or output device is a transponder. Who's to argue with that? Both descriptions are for the same piece of electronics.
Whether it's called a module, a transponder, or a wireless device, the addressable input or output device receives a signal, and responds by transmitting a different signal.
In other words, modules and other addressable conversion or translation devices are transponders.
Douglas Krantz
