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Fig. l: System installation plan of radio direction
finder IAN /CRD -61
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By J. A. FANTONI
and R. C. BENOIT, Jr.
Design of Height -Diversity
UHF Direction Finders
Automatic DF developed primarily as a navigational aid employs a unique
antenna design and height diversity reception techniques to minimize the
effects of multipath transmission on bearing accuracy and reliability.
THE transition of military
ground -to -air and air -to- ground
line -of -sight communications from
the VHF 100 to 156 Mc frequency
range to the UHF 225 to 400 MC
frequency range made necessary
the development of a ground based
direction finding facility capable of
operating in the UHF range in conjunction
with radio transmissions
from high performance type aircraft.
Development effort which
culminated in the finalized equipment
was initiated by Watson
Laboratories (later, the Rome Air
Development Center) and was pursued
jointly by the Air Force and
Federal Telecommunication Laboratories.
Analysis of Air Force operational
requirements established that engineering
effort must be directed
toward the development of a
ground based, air transportable direction
finding facility to provide
the maximum possible usable sensitivity
which would be at least
equal to contemporary communications
equipment. The facility was
also required to provide a continuous
and reliable bearing on any
signal within line -of -sight of the
installation, full automaticity, fast
bearing response time, full coverage
of the 225 to 400 MC frequency
range with a single set of antenna
elements, and flexible remoting
capabilities that needed only a
minimum number of connecting
cables. To comply with these broad
parameters, extensive engineering
effort was spent to investigate
UHF propagation characteristics,
various antenna systems, bearing
indicator techniques, and remote
control arrangements. The overall
antenna system development was
the major problem encountered
during this program. A diversity
antenna system was devised to provide
continuous bearing informa-
Fig. 2: With single antenna direct and reflected signals cancel completely
LARGE BUILDING OR HILL
SIGNAL REFLECTED
OFF NANGARIS ONLY
SIGNAL PRESENT AT
ANTENNA.
DIRECT AND REFLECTED
SIGNALS 180. OUT OF
PHASE AND CANCEL
COMPLETELY AT ANTENNA
POSITION.
J. A. SANTON/ and R. C. BENOÎT, Jr.,
Rome Air Development Center, Rome, N. Y.
65 FT FROM 20FT - 330 FT FROM 20FT
MAST
MAST
BOUNCE FOR LOWEST NULLS OCCURS AT THESE POINTS
90 Tele -Tech & ELECTRONIC INDUSTRIES June 1956