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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.
Bearing/Display/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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