PROPAGATION TIME / RESOLUTION | PROPAGATION TIME RESOLUTION 1. ROUND TRIP RANGE R L with t time to reach target 2 Rules of Thumb In one sec round trip time a The time it takes to travel to and wave travels to and from an object from an object at a distance of at a distance of - 150 m 1 m - psec - 164 yd 1 yd psec - 500 ft 1 ft psec NM 1 NM psec - km 1 km - psec 2. ONE WAY RANGE R ct with t time to reach target Time Distance Traveled Distance Time it Takes 1 milli sec ms 165 NM 1 NM psec 1 micro sec ps 1000 ft 1 km psec 1 nano sec ns 1 ft 1 ft 1 nsec 3. UNAMBIGUOUS RANGE DISTANCE BETWEEN PULSES R c PRI 2 Normally a radar measures distance to the target by measuring time from the last transmitted pulse. If the interpulse period T is long enough that isn t a problem as shown in A to the right. When the period is shortened the time to the last previous pulse is shorter than the actual time it took giving a false ambiguous shorter range figure B . Rules of Thumb RNM - 81Pms RKm - 150Pms Where Pms is PRI in milliseconds 4. RANGE RESOLUTION Rules of Thumb 500 ft per microsecond of pulse width 500 MHz IF bandwidth provides 1 ft of resolution. 5. BEST CASE PERFORMANCE The atmosphere limits the accuracy to ft The natural limit for resolution is one RF cycle. .
