Ground-to-air communications for air traffic control (ATC) are almost exclusively voice type and transmitted with AM modulation, both in the VHF and UHF bands. Today, especially in larger airports, there is a need to have numerous communication channels available, often using a single antenna or different antennas but arranged very close to each other. This makes it necessary, for the correct operation of radiocommunication equipment, to use filtering systems capable of selecting only the portion of the spectrum dedicated to the communication of interest, strongly attenuating everything else.
For these applications, given the high power involved, up to 400W peak, and the high selectivity required, a few kHz with center-band frequencies of hundreds of MHz, filter systems are realized with resonant cavities which, suitably tuned in frequency in the factory, can provide the required filtering performance.
Even though these filtering devices are purely mechanical, in some cases it is necessary to vary the operating frequency quickly and automatically, without the intervention of an operator, in order to operate with the same radio on different communication channels. For this purpose, the mechanical device is equipped with electromechanical actuators capable of changing the configuration by moving some parts, and with an electronic control board which interfaces with the radio for changing the tuning frequency of the filter when required.
Florence Engineering has been collaborating for a long time with Telmec, one of the few companies in the world capable of producing resonant cavity filters for the ATC market. The collaboration between the two companies started more than ten years ago when the need arose to design automatically tuned filters: Telmec in fact had the mechanical and electromagnetic know-how for the design and realization of the cavity, Florence Engineering provided the support for the project of the electronic and electromechanical part. From this collaboration, which has been consolidated over time, several models of automatically tuning filters were born, which today are sold under the Telmec brand and are installed in numerous airports around the world.
The key to the success of this project was the creation of a simple and reliable electromechanical control and actuation architecture, capable of operating in a wide temperature range, for many years and with a very low failure rate. In fact, automatically tuning filters are often used in emergency situations, in case of failure of other equipment, and therefore must have high availability while remaining non-operational most of the time.
This project is an excellent example of a fruitful collaboration between two Italian companies, both based in Florence, each of which contributed with its own skills and great enthusiasm to the creation of a product that is appreciated all over the world.