An antenna coupler is a device which makes it possible for one or two antennas to do the electrical work of many, as opposed to using a separate antenna for each individual wavelength. Ideally, every signal would have an individual antenna perfectly measured to resonate to its frequency. Realistically, there are hundreds of wavelengths, and it becomes impractical to equip a building with that many antennae. Technicians, therefore, change their electrical length instead of their physical length.
The process of changing an antenna's electronic abilities is known as "antenna tuning." Antenna tuning involves changing the electrical length of an antenna as well as its compatibility with various types of transmitters and receivers. To tune an antenna, technicians will use tuners, multi-couplers, and antenna couplers.
Antenna tuners and couplers perform the same essential function. Each antenna coupler is able to match one antenna with one receiver or transmitter at a time. Larger jobs are typically better suited to a multi-coupler, which as its name suggests can simultaneously match several antennae to their respective receivers and transmitters.
Over the years, many types of antenna couplers have been developed. In some cases, an automatic coupler system is installed; this device can sense when the antennae need tuning and perform the function itself. It can also adapt to become compatible with a variety of transmitters so that, on the whole, no technician is necessary. Usually, however, an automatic antenna coupler has a manual override function so that if the equipment malfunctions, a technician can come in and fix the problem.
To avoid interference, antennae systems are usually turned down to very low signal strength during tuning. The general standard is that an antenna's signal should be less than 250 watts (15000 joules/minute) when it is being tuned. This is especially true of antennae that are used in a high-frequency reception system.
One of today’s most common uses for an antenna coupler is when a homeowner wants to integrate two or more antennae as part of their TV's reception system. In this way they can combine, or "stack," their antennas, rather than having to pay for a whole new set of receptors. The TV antenna coupler matches the two antennae to one another by changing their electrical "lengths" until they are compatible. Antenna couplers can be found at most television or radio stores; in some cases they may be found at hardware stores that feature an electronics section.