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PROPAGATION TIME / RESOLUTION
1. ROUND TRIP RANGE:
with t =
time to reach target
Rules of Thumb
In one μsec round trip time, a wave travels to and from an object at a distance of: 
The time it takes to travel to and from an object at a distance of: 
≈ 150 m ≈ 164 yd ≈ 500 ft ≈ 0.08 NM ≈ 0.15 km 
≈ 1 m ≈ 0.0067 μsec ≈ 1 yd ≈ 0.006 μsec ≈ 1 ft ≈ 0.002 μsec ≈ 1 NM ≈ 12.35 μsec ≈ 1 km ≈ 6.7
μsec 
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 
6.18 μsec 
1 micro sec (μs) 
1000 ft 
1 km 
3.3 μsec 
1 nano sec (ns) 
1 ft 
1 ft 
1 nsec 
3. UNAMBIGUOUS RANGE
(DISTANCE
BETWEEN PULSES):
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 0.1 ft The natural limit for resolution is one RF cycle.
Table of Contents for Electronics Warfare and Radar Engineering Handbook
Introduction 
Abbreviations  Decibel  Duty
Cycle  Doppler Shift  Radar Horizon / Line
of Sight  Propagation Time / Resolution  Modulation
 Transforms / Wavelets  Antenna Introduction
/ Basics  Polarization  Radiation Patterns 
Frequency / Phase Effects of Antennas 
Antenna Near Field  Radiation Hazards 
Power Density  OneWay Radar Equation / RF Propagation
 TwoWay Radar Equation (Monostatic) 
Alternate TwoWay Radar Equation 
TwoWay Radar Equation (Bistatic) 
Jamming to Signal (J/S) Ratio  Constant Power [Saturated] Jamming
 Support Jamming  Radar Cross Section (RCS) 
Emission Control (EMCON)  RF Atmospheric
Absorption / Ducting  Receiver Sensitivity / Noise 
Receiver Types and Characteristics 
General Radar Display Types 
IFF  Identification  Friend or Foe  Receiver
Tests  Signal Sorting Methods and Direction Finding 
Voltage Standing Wave Ratio (VSWR) / Reflection Coefficient / Return
Loss / Mismatch Loss  Microwave Coaxial Connectors 
Power Dividers/Combiner and Directional Couplers 
Attenuators / Filters / DC Blocks 
Terminations / Dummy Loads  Circulators
and Diplexers  Mixers and Frequency Discriminators 
Detectors  Microwave Measurements 
Microwave Waveguides and Coaxial Cable 
ElectroOptics  Laser Safety 
Mach Number and Airspeed vs. Altitude Mach Number 
EMP/ Aircraft Dimensions  Data Busses  RS232 Interface
 RS422 Balanced Voltage Interface  RS485 Interface 
IEEE488 Interface Bus (HPIB/GPIB)  MILSTD1553 &
1773 Data Bus  This HTML version may be printed but not reproduced on websites.
