A diplexer, which is a form of a duplexer, is a three port frequency dependent device used for transmission or reception.
It can take different frequency bands and multiplex and demultiplex two ports and put them on one port on a single coaxial cable. Or a diplexer can route signals based on a frequency having sufficient wide band and capable of efficiently transferring them through air. A diplexer basically combines signals on a single download or perhaps links those passing through it to radio transmitters.
This passive device can also split two signals besides being on the same receive path like audio and data in digital subscriber line (DSL) telephone systems or combine two signals into one output on the same transmission path. It is also able to force a constant impedance to occupy a single broadcast frequency or allow a transmitter used by a broadcast station to operate and transmit multiple frequencies at the same time from an RF antenna.
Additionally, an antenna diplexer is an electronic component that can also be used to transmit and receive simultaneously using the same antenna – or it can allow only one antenna to be used by preventing the output of the other, or else. They allow signals such as those from an antenna and a satellite dish to share the same stream. More so, it can separate the signals based on the frequency they are using.
In contrast, diplexers are not intended for signals with overlapping frequency ranges. And if the transmitters have frequencies too close to each other, they cannot be successfully combined by a diplexer.
Typically, diplexers are used for high frequency satellite signals and low frequency CATV (cable television) / OTA (over-the-air) antenna signals. They can also be found as part of a front-end module for a mobile telecommunications system.
Diplexers are essential in trying to overcome the problem of the ban on building new transmission towers in some areas. It is very difficult these days to get permits to build new transmission towers in many places because there are laws that prohibit building towers. Many of these restrictions are caused by the Federal Aviation Administration (FAA) and Federal Communications Commission (FCC) rules for tower erection restrictions and local zoning regulations.
Although there are exceptions for companies classified as “utilities” to build even in areas where it is explicitly prohibited, in reality, building new towers today is almost impossible.
Overcoming the problem is only possible by using an existing tower as much as possible. Agreement must be reached with the owners of established transmission sites. This is where diplexers come in – by allowing two frequency bands to be transmitted together without interference.
Diplexing is a suitable solution for medium wave broadcasting stations and allows more than one transmitter such as UHF- / VHF to be used from a single pre-built tower for television reception.
It is said that diplexing AM transmitters (amplitude modulation) is easier than diplexing FM transmitters (frequency modulation) due to the fact that not all radiators will work for this type of transmissions. Antennas, in fact, must be broadband to allow transmission of the wide range of FM frequencies.
Distance is also a factor as it affects FM transmission more than AM transmission.
Due to the special care required by FM duplexing, costs could be an issue if the antenna was not already built for this type of transmission. Other factors that need to be evaluated include:
- Are the tower antennas non-directional or directional?
- How efficient is the antenna?
- Does the towing have the necessary orientation?
Examples of tower mounted diplexers (TMD) are plentiful.
An example of TMD is San Francisco’s Sutro Tower, a 977-foot steel tower used by 11 television stations, four FM radio stations, as well as satellite companies, cable providers, and wireless communications services. . Even more iconic is the Empire State Building in New York City which houses a busy diplexer that appeared in March 1952 where ABC and CBS FM stations operated from a common antenna.
The signals were diplexed into a single set of dipoles on the antenna of the latter stations near the bottom of the tower.
It is clear how diplexers are essential to allow new transmissions even if there are prohibitions on building new towers. With these devices, stations are able to prevent intermodulation and keep the voltage component of a standing wave (VSWR) to a minimum for each transmitter and input frequency, even in the presence of tower building blocks. .
Therefore, new transmissions can always be allowed.
Despite this, diplexers seem to meet both the wishes of residents who no longer want towers built and capable of serving the interests of businesses needing transmit / receive antennas for telecommunications. With this device and lens, towers can be used to provide residents with communication system capabilities and businesses with the ability to have a transmission medium to conduct their business.