BendixKing IN-862A System RDR-2100 - Manual (Page 40)

36
Effective Date: 9/98 RDR 2100 Pilot's Guide: Rev 1
Antenna Stabilization
EFFECT ON RADAR STABILIZATION
Previously discussed gyro precession errors will directly affect radar sta-
bilization, and therefore the quality of return seen on the indicator. Radar
on aircraft flying at high altitude is normally operated on the 80 to 240 nm
range with the antenna tilted down slightly so the radar beam is just
above the point of painting ground returns.
A 1/2 degree gyro error in roll during alignment would be hardly notice-
able on the horizon indicator, but with the radar operating on the 160 nm
range, it could result in almost 40 nautical miles of ground returns on one
side and no ground returns on the other.
In practice, when flying over fairly even terrain, ground returns are diffi-
cult to paint when the angle of incidence of the radiated signal becomes
large (see Looking Angle pg. 25) and, therefore, causes the beam to
travel almost parallel to the ground.See the figure below.
The vertical gyro is designed to sense verticality within 1/2 degree under
normal operating conditions. Perfect radar antenna stabilization requires
the following accuracies: the vertical gyro must maintain exact verticality,
the antenna mounting bracket must be leveled perfectly to coincide with
the gyro mounting base, the elevation servo amplifiers must be balanced
precisely with a sharp null (no dead band at null position), antenna
follow-up signals must be linear over the full range of the antenna tilt,
and the antenna must be adjusted properly with no backlash (play) in the
elevations gear train. Even though extreme care is used during overhaul
and adjustment of the equipment, minute variations can be cumulative,
resulting in small stabilization errors.
If ground returns appear on one side first as the antenna tilt is lowered,
continue lowering the tilt until ground returns are visible on the other side;
if the difference in tilt is 2 degrees or less, the antenna can be tilted up to
clear the ground returns with satisfactory radar operation. Differences
greater than 2 degrees warrant corrective action, assuming proper gyro
stabilization in level flight.
The following information on radar operation during aircraft maneuvers
may be helpful.
RDR 2100 PG 3/12/07 3:45 PM Page 36