# Pulse repetition frequency

PRFpulse repetition frequenciesmedium pulse repetition frequencypulse repetition rateinter-pulse periodlow PRFpulse lengthPulse Repetition Intervalpulse-repetition frequencypulse-repetition interval (PRI)
The pulse repetition frequency (PRF) is the number of pulses of a repeating signal in a specific time unit, normally measured in pulses per second.wikipedia
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Radar warning receivers in aircraft include a library of common PRFs which can identify not only the type of radar, but in some cases the mode of operation.
The receiver periodically scans across the frequency band and determines various parameters of the received signals, like frequency, signal shape, direction of arrival, pulse repetition frequency, etc. By using these measurements, the signals are first deinterleaved to sort the mixture of incoming signals by emitter type.

The pulse repetition frequency (PRF) is the number of pulses of a repeating signal in a specific time unit, normally measured in pulses per second. The term is used within a number of technical disciplines, notably radar.
The maximum non-ambiguous range, which is determined by the pulse repetition frequency. The maximum non-ambiguous range is the distance the pulse could travel and return before the next pulse is emitted.

### Range ambiguity resolution

Range ambiguity resolution detailed explanationrange ambiguity resolution process
The range ambiguity resolution process is used to identify true range when PRF is above this limit.
Range ambiguity resolution is a technique used with medium Pulse repetition frequency (PRF) radar to obtain range information for distances that exceed the distance between transmit pulses.

### Frequency ambiguity resolution

ambiguous velocityFrequency ambiguity resolution detailed explanationFrequency ambiguity resolution process explanation
For example, an L-Band radar with 500 Hz pulse rate produces ambiguous velocity above 75 m/s (170 mile/hour), while detecting true range up to 300 km. This combination is appropriate for civilian aircraft radar and weather radar.
Frequency ambiguity resolution is used to find true target velocity for medium pulse repetition frequency (PRF) radar systems.

Dopplerpulse-Dopplerpulse doppler
Medium PRF is used with Pulse-Doppler radar, which is required for look-down/shoot-down capability in military systems.
Pulse-Doppler radar was developed during World War II to overcome limitations by increasing pulse repetition frequency.

### Moving target indication

moving target indicatorground moving target indicationMTI
Moving target indicator is generally required for acceptable performance near terrain, but this introduces radar scalloping issues that complicate the receiver.
Early MTI systems generally used an acoustic delay line to store a single pulse of the received signal for exactly the time between broadcasts (the pulse repetition frequency).

scallopingblind velocities
Moving target indicator is generally required for acceptable performance near terrain, but this introduces radar scalloping issues that complicate the receiver.
This occurs near multiples of 15 m/s for an L-Band radar with pulse repetition frequency of 1kHz (10m/s to 20m/s, 25m/s to 35m/s, 40m/s to 50m/s, and so on).

### Ambiguity resolution

Ambiguity resolution detailed explanationAmbiguity resolution process explanation
A technique called ambiguity resolution is required to identify true range and speed.
Pulse repetition frequency (PRF) is too low to sample Doppler frequency directly

### Carrier frequency

command frequenciescarrier frequenciesfrequencies
In radar, a radio signal of a particular carrier frequency is turned on and off; the term "frequency" refers to the carrier, while the PRF refers to the number of switches.

### Cycle per second

kilocyclecycles per secondkilocycles
Both are measured in terms of cycle per second, or hertz.

### Hertz

MHzkHzHz
Both are measured in terms of cycle per second, or hertz.

### World War II

Second World WarwarWWII
For instance, a typical World War II radar like the Type 7 GCI radar had a basic carrier frequency of 209 MHz (209 million cycles per second) and a PRF of 300 or 500 pulses per second.

pulse widthfrequency spectrumfrequency, pulse repetition rate, and other characteristics
A related measure is the pulse width, the amount of time the transmitter is turned on during each pulse.

### Electronic warfare

EWelectronicelectronic attack
This gives each radar system a characteristic PRF, which can be used in electronic warfare to identify the type or class of a particular platform such as a ship or aircraft, or in some cases, a particular unit.

### S-75 Dvina

SA-2S-75SA-2 Guideline
This allowed pilots to be warned when an SA-2 SAM battery had "locked on", for instance.

### Sonar

asdicvariable depth sonaractive sonar
Sonar and lidar systems also have PRFs, as does any pulsed system.

### Lidar

laser altimeterlaser radarlight detection and ranging
Sonar and lidar systems also have PRFs, as does any pulsed system.

### Fourier analysis

FourierFourier analyzeranalyse the output wave into its constituent harmonics
Electromagnetic (radio or sound) waves are conceptually pure single frequency phenomena while pulses may be mathematically thought of as composed of a number of pure frequencies that sum and nullify in interactions that create a pulse train of the specific amplitudes, PRRs, base frequencies, phase characteristics, et cetera (See Fourier Analysis).

### Electrical engineering

electrical engineerelectricalelectrical engineers
The first term (PRF) is more common in device technical literature (Electrical Engineering and some sciences), and the latter (PRR) more commonly used in military-aerospace terminology (especially United States armed forces terminologies) and equipment specifications such as training and technical manuals for radar and sonar systems.

### Terminology

termtermsterminologies
The first term (PRF) is more common in device technical literature (Electrical Engineering and some sciences), and the latter (PRR) more commonly used in military-aerospace terminology (especially United States armed forces terminologies) and equipment specifications such as training and technical manuals for radar and sonar systems.

### Multiplicative inverse

reciprocalinversereciprocals
The reciprocal of PRF (or PRR) is called the pulse repetition time (PRT), pulse repetition interval (PRI), or inter-pulse period (IPP), which is the elapsed time from the beginning of one pulse to the beginning of the next pulse.

### Doppler effect

Dopplerdoppler shiftDoppler shifts
For example, the APY-1 radar used 128 IPP's with a fixed 50 range gates, producing 128 Doppler filters using an FFT.

### Tachometer

rev counterrev-countercounter
For example, a tachometer may use a strobe light with an adjustable PRF to measure rotational velocity.

### Strobe light

strobestrobe lightsstrobes
For example, a tachometer may use a strobe light with an adjustable PRF to measure rotational velocity.

### Laser rangefinder

laser range finderlaser ranginglaser range-finder
Laser range finder