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Servo Radio Direction Finder Products

Designed and built to the rigid electrical and mechanical specifications of the U.S. Federal Aviation Administration and certified for use under extreme environmental conditions, Servo DF systems for both UHF and VHF, are currently in use in hundreds of locations throughout the world. These systems, over the past 30 years, have with stood searing temperatures in deserts of Egypt, hurricanes in the Caribbean and freezing snow, wind and ice conditions in Alaska and Canada.

Developed in the 1940's by Servo Corporation, the Quasi-Doppler DF concept simulates the effect of a revolving single dipole antenna around the circumference of a circle. In this case the vertically polarized dipoles are electrically commutated to phase modulate the individually received signals on a sampled data basis. This phase modulation produces a DF sine wave of approximately 250 Hz which has a phase relationship proportional to the angle of arrival of the DF signal. The results are displayed instantaneously in the digital bearing readout and ring-of-light display on both the Receiver/Bearing Processor and the Bearing Display/Control Assembly.

Detailed Equipment Description

The Receiver/Bearing Processor is installed at the antenna site and connected via cables to the DF antenna. It is a rack-mounted unit which contains all the necessary electronic equipment to receive and process RF signals. For UHF/VHF operation, two of these devices are required. Although the units look identical they are specifically tuned for their unique operation.

Received RF signals are converted to a digital output suitable to drive the Bearing and Ring-of-Lights displays on the front panel of the unit, and for transmission via a system specified modem over voice-grade telephone lines to a remote control site equipped with a Bearing Display/Control Assembly. Controls and displays located on he Bearing Display/Control Assembly are identical to those on the receiver processor. However, system control is limited to one site only (either local or remote) as determined by the setting of the LOCAL push-button switch on the Receiver Processor Assembly. Bearing, frequency and other status information is displayed at both sites regardless of which has control.


The Bearing Display/Control Unit is installed at the operations site (e.g. Control tower) and connected via a 4 wire voice grade telephone line circuit to the Receiver/Bearing Processor unit located at the antenna site. It is a rack-mounted unit which is similar in physical appearance to the Receiver/Bearing Processor Assembly. The unit contains all circuits necessary to remotely control tuning of the receiver (located in the Receiver/Bearing Processor Assembly) and to receive and display the receiver channel frequency as well as status and bearing data through the use of the modem and associated 4-wire telephone circuit. The Bearing Display/ Control Assembly will display either VHF or UHF signals depending upon the position of the optional VHF/UHF switch setting on the unit. Except for the VHF/UHF optional switch and the REMOTE/Local selector switch, all other front panel functions are the same as those of the Receiver/Bearing Processor Assembly.

2.3 Antenna Assembly (About DF Antennas)

The Series 2100 antenna system comes in various options: 16 element VHF, 8 element VHF, 16 element UHF and combination 32 element UHF/VHF assembly.




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