4-25
The SPECTRUM ANALYZER and the ECHO BOX are two instruments used to check transmitter
performance.
One of the more important measurements that can be performed with the echo box is RING TIME.
Ring time gives a relative indication of both transmitter output power and receiver sensitivity.
Transmitter OUTPUT POWER MEASUREMENTS are a good indication of overall transmitter
operation. POWER MEASUREMENTS are usually of average power read in dBm. The average power
dBm reading must be converted to watts and the peak power calculated. The formula for peak power is:
RECEIVER PERFORMANCE CHECKS determine receiver sensitivity, tr recovery time, and
receiver bandwidth.
You usually measure receiver sensitivity by measuring the MINIMUM DISCERNIBLE SIGNAL
(mds) using the pulse method.
TR RECOVERY time is the time required for the tr tube to DEIONIZE after each transmitted pulse.
You should keep a graph of tr recovery time to determine when the tr tube should be replaced. If not
replaced in a timely manner, a weak tr tube will allow damage to the radar receiver.
Few radars can function without SUPPORT SYSTEMS. These support systems include
ELECTRICAL POWER, DRY-AIR, and LIQUID-COOLING SYSTEMS.
The radar technician should learn the source and distribution routes for NORMAL and
EMERGENCY POWER for the radar.
The DRY AIR needed for electronic equipment can be supplied by the ship's electronics dry-air
system through an air control panel or from local dehydrators.
Radar transmitters generate large amounts of heat. Most of this heat is dissipated by a combination of
AIR CONDITIONING, CABINET AIR BLOWERS, and a DISTILLED-WATER COOLING system.
