Police traffic radar using absolute signal strength information to improve target signal processing accuracy

• US 5,570,093 A
• Filed: 02/10/1995
• Issued: 10/29/1996
• Est. Priority Date: 02/10/1995
• Status: Expired due to Term

• Current Assignee: Applied Concepts Incorporated (Emerson Electric Company)
• Original Assignee: Applied Concepts Incorporated (Emerson Electric Company)
• Inventors: Gammenthaler, Robert S., Aker, John L., Mead, Alan B.
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US08/386,552
• Time in Patent Office: 627 Days
• Field of Search: 342/104, 342/112, 342/115, 342/114, 342/116, 342/196
• US Class Current: 342/104
• CPC Class Codes: G01S 13/58 Velocity or trajectory determination systems; Sense-of-movement determination systems
• CPC Class Codes: G01S 13/583 using transmission of continuous unmodulated waves, amplitude-, frequency-, or phase-modulated waves and based upon the Doppler effect resulting from movement of targets
• CPC Class Codes: G01S 13/92 for velocity measurement
• CPC Class Codes: G01S 7/003 Transmission of data between radar, sonar or lidar systems and remote stations
• CPC Class Codes: G01S 7/032 Constructional details for solid-state radar subsystems
• CPC Class Codes: G01S 7/285 Receivers
• CPC Class Codes: G01S 7/352 Receivers
• CPC Class Codes: G01S 7/354 Extracting wanted echo-signals Doppler systems G01S13/50
• CPC Class Codes: G01S 7/356 involving particularities of FFT processing

Abstract

A police radar utilizing digital data transmission from the antenna unit to a separately housed counting and display unit. The antenna has a double balanced mixer to suppress even order harmonics. The counting and display unit has a computer programmed to perform digital signal processing on the digital data received from the antenna to improve the quality and accuracy of calculated speeds for patrol speed, strongest target speed and fastest target speed. Fastest target speed can be displayed simultaneously with strongest target speed. Signal processing techniques are used to suppress false signals caused by double and triple bounce, harmonics, intermodulation products, video display terminal interference, etc.

Claims

1. A police traffic surveillance radar, comprising:

an antenna unit for transmitting radar signals and receiving a spectrum of radar signals reflected from stationary and moving objects and having a variable gain amplifier having a gain control signal input for receiving a gain control signal, said amplifier for amplifying said received spectrum of radar signals;

means coupled to said gain control signal input for generating said gain control signal based upon a comparison of the amplitude of received radar signals to predetermined upper and lower limits;

a frequency counting and display unit having at least one display window;

digital data transmission path coupling said antenna unit to said frequency counting and display unit;

digitizing means coupled to said antenna unit for digitizing said spectrum of received radar signals reflected from stationary and moving objects and transmitting the digital data resulting therefrom to said frequency counting and display unit via said digital data transmission path;

and wherein said antenna unit and said frequency counting and display unit are in separate housings;

and wherein said frequency counting and display unit includes a computer coupled to said means for generating said gain control signal and programmed to compute and display patrol car speed by determining the gain setting for a plurality of samples of digital data and collecting a predetermined number of samples of said digital data generated at said gain setting and then perform a plurality of overlapping Fast Fourier Transforms using Hamming windows on said samples to generate a plurality of spectral components each of which is represented by a real and an imaginary component, and programmed to calculate the apparent power or a function of the apparent power of each spectral component, and programmed to select the spectral component having the highest apparent power as a patrol speed candidate signal, and programmed to calculate the true power thereof using the relationship

space="preserve" listing-type="equation">T=A×

10.sup.(G/10)

where

T=true power of the spectral line having the highest apparent power

A=apparent power or a function of the apparent power of the spectral component

G=the gain adjustment established by said gain control signal,

said computer also programmed to eliminate said patrol speed candidate'"'"'s spectral component from further processing to calculate patrol speed if said true power thereof is unacceptably low, but if the signal power of said patrol speed candidate spectral component is acceptable, said computer programmed to calculate the patrol speed from said selected patrol speed spectral component.

2. The apparatus of claim 1 wherein said computer is also programmed to reject the spectral line having the highest apparent power if the true power thereof indicates an unacceptably high probability that said spectral line is a false signal generated by a double or triple bounce of the transmitted radar signal, or is a harmonic or is an intermodulation product.

3. The apparatus of claim 1 wherein said computer is also programmed to remove the patrol speed spectral components from which patrol speed was calculated from said spectrum, and programmed to thereafter compute the speed of the moving target from which the strongest reflected radar signals have been received which meet predetermined selection criteria, said calculation being performed by averaging the results of said overlapping Fast Fourier Transform calculations so as to generate a plurality of spectral components hereafter called the spectrum, said computer also programmed to calculate the power of each spectral component in said spectrum, and programmed to calculate the average power of a plurality of neighboring spectral components above and below the frequency of each said spectral component in the spectrum, and programmed to apply target selection criteria to each said spectral component in said spectrum by examining the signal-to-noise attributes of each said spectral component by at least comparing the power of each spectral component in said spectrum to the average power of said plurality of neighboring spectral components and reject any said spectral component as a target return candidate if the power thereof is not more than said average power of said plurality of neighboring spectral components by an acceptable margin, and programmed to compare the true power of said spectral component from which said patrol speed was calculated, and if said true power is above a predetermined limit, for raising the acceptable margin for said signal-to-noise attributes for any spectral component having a frequency which is an integer multiple of the frequency of said spectral component from which said patrol speed was calculated.

4. The apparatus of claim 3 wherein said computer is also programmed to select a spectral component representing the fastest moving target whose reflected radar signal meets predetermined selection criteria for a fastest target speed display and programmed to calculate and display the speed of said fastest target signal, said computer programmed to carry out this function by selecting a predetermined number of spectral components representing the fastest moving target candidates and arranging said fastest moving target candidates in order of descending speed and doing a top elimination starting with the fastest candidate to eliminate any which do not meet predetermined signal-to-noise power selection criteria, and, if said true power of said patrol speed spectral component is above a predetermined limit, subjecting each remaining fastest speed candidate in order of descending speed and which has a spectral component frequency which is either two or three times the frequency of said patrol speed spectral component to a signal-to-noise selection criteria the stringency of which increases with increasing true power of said patrol speed spectral component and eliminating any candidate which does not have a signal-to-noise ratio better than said selection criteria, said computer programmed to calculate the true power of a predetermined number of strongest spectral components in said spectrum after removal of said patrol speed spectral component, and programmed to compare said true power of said predetermined number of strongest spectral components in said spectrum after removal of said patrol speed spectral component to a harmonic generation threshold, and if any of said strongest spectral components have a true power greater than said harmonic generation threshold, subjecting any remaining fastest speed candidate in descending order of speed and which has a frequency which is an integer multiple of the frequency of said strongest spectral component which has a true power above said harmonic generation threshold to a new fastest signal-to-noise selection criteria the stringency of which increases with increasing true power of said strongest spectral component which has a true power above said harmonic generation threshold and eliminating any fastest candidate having a signal-to-noise attribute which is worse than said new fastest signal-to-noise selection criteria, and programmed to subject any remaining fastest speed candidate in decreasing order of speed to intermodulation product selection criteria by determining if any of said strongest spectral component has a true power above said intermodulation product generation threshold and, if any remaining fastest speed candidate has a frequency which is either the sum or difference in frequency between any of said strongest spectral components which has a true power above said intermodulation product generation threshold and any of said strongest spectral components which has a true power above said harmonic generation threshold, eliminating said fastest speed candidate and displaying any remaining fastest speed candidate.

5. The apparatus of claim 4 wherein said frequency counting and display unit has two displays and wherein said computer is programmed to display said calculated speed of the moving target from which the strongest reflected radar signals have been received which meet predetermined selection criteria in one of said displays and is programmed to simultaneously display said calculated speed of any surviving fastest speed candidate signal reflected from a moving target on the other said display.

6. The apparatus of claim 4 wherein said frequency counting and display unit has three displays and wherein said computer is programmed to display said calculated speed of the moving target from which the strongest reflected radar signals have been received which meet predetermined selection criteria in one of said displays and is programmed to simultaneously display said calculated speed of any surviving fastest speed candidate signal reflected from a moving target on another of said displays, and is programmed to simultaneously display said calculated patrol speed on the third of said displays.

7. A method for measuring and displaying the speed of objects which reflect radar signals to a police radar unit, said police radar unit having an antenna unit comprising a transmitter section and a receiver section, said receiver section having mixer diodes for mixing a local oscillator signal with received reflected radar signals and having an amplifier section with variable gain and an analog-to-digital converter for converting received signals to a plurality of digital sample words, and having a counting/display unit coupled to said antenna unit by a serial data link having at least one display window for displaying a calculated speed and remotely located from said antenna unit by a distance of more than one foot, said receiver section including serial data transmission circuitry for sending said digital data samples to said counting/display unit as frames of serial data, and said counting/display unit including circuitry for sending digital data in serial format to said antenna unit, comprising the steps of:

sending a digital gain control signal from said counting/display unit to said remotely located antenna unit as serial data on said serial data link for purposes of controlling the gain of said amplifier in said antenna unit, and recording the value of said digital gain control signal;

transmitting radar signals from said antenna unit and receiving reflected radar signals in said antenna unit and amplifying said reflected radar signals using said amplifier in said receiver section with the gain thereof set at the gain level encoded in said digital gain control signals received as serial data received from said counting/display unit, and converting the amplitude and frequency of said reflected radar signals to a plurality of digital sample words;

transmitting said digital sample words as serial data from said antenna unit to said counting/display unit as a plurality of frames of serial format data;

receiving said digital sample words from said antenna unit and storing a predetermined number of said sample words as a data block in a memory and recording in memory the gain level encoded in said digital gain control signal at which said amplifier of said antenna unit was operating when the digital sample words stored in said data block were generated;

analyzing said sample words in said data block to determine the relative signal strength of the received reflected radar signals, and if the relative signal strength of any received reflected radar signal is above a predetermined upper limit, generating a new digital gain control signal to lower the gain of said amplifier, and, if the relative signal strength of all received reflected radar signals are below a predetermined lower limit, generating a new digital gain control signal to raise the gain of said amplifier, and then determining the speed of movement of said radar unit and processing said sample words in said data block to determine the relative closing speed of a plurality of the strongest received target signals;

for each of said strongest received target signals, calculating the average local noise power in a predetermined range of frequencies around the frequency of each said strongest received target signal;

calculating the noise power to signal power ratio for each of said strongest received target signals using the average local noise power calculated in the preceding step; and

calculating the true power of each of said plurality of the strongest received signals using the relationship

space="preserve" listing-type="equation">T=A×

10.sup.(G/10)

where,

T=true power at the output of said mixer diodes,

A=apparent power of the received signal representing patrol car speed,

G=the gain adjustment recorded in memory and encoded in said digital gain control signal sent to said antenna unit by said counting/display unit that resulted in said digital sample words in said data block;

using said true power of each of said plurality of strongest received signals to determine if there is a possibility that said strongest received signal may be a false signal;

rejecting any of said plurality of strongest received signals which is not a signal representing patrol car speed to eliminate display thereof if said strongest received signal is a false signal generated by harmonics or intermodulation products of one or more of said strongest received signals;

if said noise power to signal power ratio for the strongest of said strongest received received signals remaining after the screening imposed by the step next above is below a predetermined threshold, and the result of the screening step next above indicates that said strongest received target signal is not likely to be a false signal, calculating and displaying on said display window of said counting/display unit the speed of said strongest received target signal by combining the speed of said patrol car and said relative closing speed of said strongest received target signal which passes all the aforementioned tests.

10. The method of claim 7 wherein said antenna unit includes hysteresis type line receivers coupled to receive serial data from said counting/display unit, and wherein said counting/display unit includes hysteresis type line receivers coupled to receive serial data from said antenna unit, and wherein said method includes the steps of:

receiving said digital gain control commands from said counting/display unit using said hysteresis type line receivers to improve the signal-to-noise ration of data received from said counting/display unit;

receiving said digital serial format sample data words from said antenna unit using said hysteresis type line receivers to improve the signal-to-noise ratio of data received from said antenna unit.

8. A method for measuring and displaying the speed of objects which reflect radar signals to a police radar unit, said police radar unit having an antenna unit comprising a transmitter section and a receiver section, said receiver section having mixer diodes for mixing a local oscillator signal with received reflected radar signals and having an amplifier section with variable gain and an analog-to-digital converter for converting received signals to a plurality of digital sample words, and having a counting/display unit coupled to said antenna unit by a serial data link having at least first and second display windows for displaying calculated speeds and remotely located from said antenna unit by a distance of more than one foot, said receiver section including serial data transmission circuitry for sending said digital data samples to said counting/display unit as frames of serial data, and said counting/display unit including circuitry for sending digital data in serial format to said antenna unit, comprising the steps of:

(1) sending a digital gain control signal from said counting/display unit to said remotely located antenna unit as serial data on said serial data link for purposes of controlling the gain of said amplifier in said antenna unit, and recording the value of said digital gain control signal;

(2) transmitting radar signals from said antenna unit and receiving reflected radar signals in said antenna unit and amplifying said reflected radar signals using said amplifier in said receiver section with the gain thereof set at the gain level encoded in said digital gain control signals received as serial data received from said counting/display unit, and converting the amplitude and frequency of said reflected radar signals to a plurality of digital sample words;

(3) transmitting said digital sample words from said antenna unit to said counting/display unit as a plurality of frames of serial format data;

(4) receiving said digital sample words from said antenna unit and storing a predetermined number of said sample words as a data block in a memory and recording in memory the gain level encoded in said digital gain control signal at which said amplifier of said antenna unit was operating when the digital sample words stored in said data block were generated;

(5) analyzing said sample words in said data block to determine the relative signal strength of the received reflected radar signals, and if the relative signal strength of any received reflected radar signal is above a predetermined upper limit, generating a new digital gain control signal to lower the gain of said amplifier, and, if the relative signal strength of all received reflected radar signals are below a predetermined lower limit, generating a new digital gain control signal to raise the gain of said amplifier, and then determining the speed of movement of said radar unit and processing said sample words in said data block using Fourier analysis to generate a spectrum of spectral lines each of which has an amplitude and a frequency, said spectrum encoding all received signals, and examining said spectrum to determine the strongest received target signal which does not represent the speed of said patrol car and the relative closing speed of the strongest received target signal;

(6) calculating the local noise power in a predetermined range of frequencies around the frequency of said strongest received target signal;

(7) calculating the noise power to signal power ratio for said strongest received target signal using the noise power calculated in the preceding step; and

(8) calculating the true power of each of a predetermined number of the strongest received signals using the relationship

space="preserve" listing-type="equation">T=A×

10.sup.(G/10)

where,

T=true power at the output of said mixer diodes,

A=apparent power of the received signal representing patrol car speed,

G=the gain adjustment recorded in memory and encoded in said digital gain control signal sent to said antenna unit by said counting/display unit that resulted in said digital sample words in said data block;

(9) using said true power of each of said predetermined number of strongest received signals to determine if there is a possibility that said strongest received signal may be a false signal;

(10) screening the strongest received signal which is not a signal representing patrol car speed to eliminate display thereof if said strongest received signal is a false signal generated because of the strength of one of said predetermined number of strong received signals;

(11) if said noise power to signal power ratio for said strongest received target signal is below a predetermined threshold, and the result of the screening step next above indicates that said strongest received target signal is not likely to be a false signal, calculating and displaying on said display window of said counting/display unit the speed of said strongest received target signal by combining the speed of said patrol car and said relative closing speed in an appropriate manner depending upon whether the target which generated said strongest received target signal is moving in the same general direction as said patrol car or in an opposite general direction;

(12) searching said spectrum generated by said Fourier analysis for spectral line patterns that represent received signals of the highest frequency representing the fastest moving targets which have generated reflected radar signals, and storing the spectral line numbers of a predetermined number of said received signals in a table in memory in order of descending frequency representing decreasing target speed;

(13) calculating for each signal stored in said table the ratio of a local noise power maximum in a local noise power maximum range of frequencies adjacent said signal stored in said table to the signal power of said signal stored in said table, said local noise power maximum being the highest signal power for any signal found in said local noise power maximum range of frequencies adjacent the signal stored in said table being processed and storing the result in said table;

(14) calculating for each signal stored in said table the average local noise power of the spectral lines in a predetermined range of frequencies above the frequency of the highest frequency signal stored in said table and a predetermined range of frequencies below the frequency of the highest frequency signal stored in said table, and calculating the ratio of average local noise power to signal power of the signal stored in said table for each said signal stored in said table and storing the results in said table;

(15) comparing the noise power to signal power ratio for the highest frequency signal stored in said table to a predetermined threshold, and rejecting the highest frequency signal stored in said table if said noise power to signal power ratio for said highest frequency signal stored in said table is greater than said predetermined threshold;

(16) if said noise power to signal power ratio for said highest frequency signal stored in said table is less than said predetermined threshold, retrieving a ratio from a plurality of acceptable local-noise-maximum/signal ratios stored in a selected table in memory and calculating whether the ratio of said local noise power maximum to said signal power corresponding to said highest frequency signal stored in said table is less than said ratio retrieved from said memory, and rejecting said highest frequency signal stored in said table as a preliminary fastest target speed candidate if the ratio of said local noise power maximum to said signal power of said highest frequency signal stored in said table is greater than said ratio retrieved from said table and selecting the next highest frequency signal stored in said table and repeating steps (15)-(16) for each other signal stored in said table until a preliminary fastest speed candidate is found which passes the tests of steps (15) and (16);

(17) performing predetermined other qualification tests on the first fastest speed candidate that passes the tests imposed by steps (15) and (16), and if, all said qualification tests are passed, calculating the speed of said fastest speed candidate and making it available for selective display.

11. The method of claim 8 further comprising the step of screening the fastest speed candidate to eliminate display thereof if said fastest speed candidate is a false signal generated because of the strength of a combination of two or more of said predetermined number of said strongest received signals.

12. The method of claim 8 wherein said step of screening each fastest speed candidate to eliminate display thereof if said fastest speed candidate is a signal resulting from double or triple bounce of transmitted radar energy between any object and the radar unit.

9. A method for measuring the speed of objects which reflect radar signals to a police radar unit, said police radar unit having an antenna unit comprising a transmitter section and a receiver section, said receive section having an amplifier section with variable gain and an analog-to-digital converter for converting received signals to a plurality of digital sample words, and having a counting/display unit coupled to said antenna unit by a serial data link and remotely located from said antenna unit by a distance of more than one foot, said receiver section including serial data transmission circuitry for sending said digital data samples to said counting/display unit as frames of serial data, and said counting/display unit including circuitry for sending digital data in serial format to said antenna unit, comprising the step of:

sending a digital gain control signal from said counting/display unit to said remotely located antenna unit as serial data on said serial data link for purposes of controlling the gain of said amplifier in said antenna unit;

transmitting radar signals from said antenna unit and receiving reflected radar signals in said antenna unit and amplifying said reflected radar signals using said amplifier in said receiver section with the gain thereof set at the gain level encoded in said digital gain control signals received as serial data received from said counting/display unit, and converting the amplitude and frequency of said reflected radar signals to a plurality of digital sample words;

transmitting said digital sample words as serial data from said antenna unit to said counting/display unit as a plurality of frames of serial format data;

receiving said digital sample words from said antenna unit and storing a predetermined number of said sample words as a data block in a memory;

analyzing said sample words in said data block to determine the relative signal strength of the received reflected radar signals, and if the relative signal strength of any received reflected radar signal is above a predetermined upper limit, generating a new digital gain control signal to lower the gain of said amplifier, and if the relative signal strength of all received reflected radar signals are below a predetermined lower limit, generating a new digital gain control signal to raise the gain of said amplifier, and then determines the speed of movement of said radar unit and processing said sample words in said data block to determine the relative closing speed of the strongest;

received target signal; and

calculating and displaying on a display of said counting/display unit the speed of said strongest received target signal by combining the speed of said patrol car and said relative closing speed in an appropriate manner depending upon whether the target which generated said strongest received target signal is moving in the same general direction as said patrol car or in an opposite general direction.

13. The method of claim 9 further comprising the step of screening the fastest speed candidate to eliminate display thereof if said fastest speed candidate resulting from harmonic distortion of one of said predetermined number of the strongest received signals.

14. The method of claim 9 further comprising step of screening the fastest speed candidate to eliminate display thereof if said fastest speed candidate is a signal resulting from intermodulation products between a combination of two or more of said predetermined number of the strongest received signals.

15. The method of claim 9 further comprising the step of screening the fastest speed candidate to eliminate display thereof if said fastest speed candidate is a potential double bounce false signal having an apparent closing speed twice the speed of said patrol car if the true power of the received signal representing said patrol car speed is above a predetermined threshold, and, if the true power of the received signal representing said patrol car speed signal is below said predetermined threshold, then displaying said fastest speed candidate.

16. A traffic surveillance radar having an antenna unit which receives reflected radar signals and generates digital data encoding said received reflected radar signals, said antenna housed in a first housing and coupled by a cable to a counting and display unit housed in a second housing which is distinct from said first housing, said counting and display unit including a computer programmed to receive said digital data transmitted from said antenna unit via said cable and performing Fourier Transform calculations on a plurality of said digital data to generate a digital frequency spectrum comprised of a plurality of discrete spectral lines, some of which represent legitimate targets in the form of reflected Doppler radar signals representing the speed of said legitimate targets relative to the speed of said traffic surveillance radar, and some of which represent ground speed of the traffic surveillance radar in the form of reflected Doppler radar signals representing the speed of the traffic surveillance radar relative to stationary objects and some of which may represent false signals, harmonics or intermodulation products which do not represent valid targets, said computer in said counting and display unit programmed to process the plurality of discrete spectral lines by performing a Fourier Transform analysis to find a plurality of the highest amplitude spectral lines at low frequencies representing low speeds and tracking the highest amplitude of these high-amplitude, low frequency spectral lines as said ground speed of said traffic surveillance radar (hereafter referred to as simply ground speed), said computer in said counting and display unit also programmed to calculate and display said ground speed from said high-amplitude, low frequency spectral line being tracked, and said computer programmed to filter out this plurality of high-amplitude, low frequency spectral lines representing candidates for said ground speed and analyze the remaining spectral lines (hereafter referred to as the remaining spectral lines) Fourier Transform analysis to find the highest amplitude spectral line representing the speed of a legitimate target which also passes quality assurance tests comprising determining if the candidate spectral line has an acceptable signal-to-noise ratio and also does not have a frequency which represents a speed which is approximately an integer multiple of said ground speed, said computer in said counting and display unit also programmed to calculate and display the speed of the legitimate target represented by the highest amplitude spectral line which passed all said quality assurance tests (hereafter referred to as the strongest target speed).

17. The apparatus of claim 16 wherein said computer is programmed to perform overlapping Fast Fourier Transform calculations in finding the highest amplitude spectral line which passed said quality assurance tests, and wherein said counting and display unit has at least three displays one of which is used to display said ground speed and one of which is used to display said strongest target speed, and wherein said computer is also programmed to select from said remaining spectral lines a plurality of spectral lines having frequencies apparently representing the fastest targets (hereafter referred to as the fastest candidates), and wherein said computer is programmed to pass each of said fastest candidates, in order of descending speed, through a plurality of qualification tests comprising:

rejecting the fastest candidate if it has a signal-to-noise ratio lower than a predetermined threshold;

rejecting the fastest candidate if it has a frequency which is within a predetermined range of the frequency other high amplitude spectral lines in the vicinity of the frequency of said fastest candidate;

rejecting any fastest candidate which could possibly have been caused by radio frequency interference;

rejecting said fastest candidate if it has an apparent speed which is approximately an integer multiple of the currently displayed strongest target speed;

rejecting the fastest speed candidate if it has an apparent speed which is either 2 or 3 times the ground speed and the amplitude of the spectral line from which said ground speed was calculated is above a predetermined threshold and the fastest candidate either has a signal-to-noise ratio which is below a determined threshold or does not persist long enough;

rejecting the fastest speed candidate if the amplitudes of a plurality of the highest amplitude spectral lines (hereafter referred to as the strongest signals) have amplitudes above a predetermined level and said fastest speed candidate is possibly a harmonic of one of the strongest signals or is possibly an intermodulation product of any combination of the strongest signals;

said computer also programmed to calculate and display the speed of the first fastest candidate that passes all said qualification tests in said third display if said third display is not currently displaying another target speed and if the same fastest candidate passed all said qualification tests at least twice on successive iterations of the fastest candidate qualification tests, each iteration starting with a new set of spectral lines calculated from radar return data received at different, adjacent times, and if said traffic surveillance radar has been operating for at least a predetermined time and if no radio frequency interference was detected during reception of the radar return data from which the fastest candidate which passed all said qualification tests was selected.

18. A traffic surveillance radar having an antenna unit which receives reflected radar signals and generates digital data encoding said received reflected radar signals, said antenna housed in a first housing and coupled by a cable to a counting and display unit housed in a second housing which is distinct from said first housing, said counting and display unit including a computer programmed to receive said digital data transmitted from said antenna unit via said cable and performing at least one Fast Fourier Transform calculation on a plurality of said digital data and programmed to calculate the signal-to-noise ratios of a plurality of spectral components resulting from said Fast Fourier Transform calculation by calculating the signal power of each of said plurality of spectral components and the average noise power of a plurality of neighboring spectral components both above and below the frequency of each said spectral component in said plurality of spectral components, and calculating the ratio of the signal power of each said spectral component in said plurality of spectral components to said average noise power of said neighboring spectral components, and eliminating any spectral component as a valid candidate for target speed calculation processing which has a signal-to-average noise power attribute below an acceptable minimum.

19. A traffic surveillance radar having an antenna unit which receives reflected radar signals and generates digital data encoding said received reflected radar signals, said antenna housed in a first housing and coupled by a cable to a counting and display unit housed in a second housing which is distinct from said first housing, said counting and display unit including a computer programmed to receive said digital data transmitted from said antenna unit via said cable and performing at least one Fast Fourier Transform calculation on a plurality of said digital data and programmed to calculate the local noise maximum of a plurality of the highest frequency spectral components resulting from said Fast Fourier Transform calculation by calculating the signal power of each of said plurality of spectral components of the highest frequency and the signal power of any weaker signal in a neighboring range of frequencies above and below the frequency of the spectral component being analyzed, and calculating the ratio of the signal power to the power of any weaker signal in said neighborhood of said spectral component being analyzed.

20. A traffic surveillance radar having an antenna unit which receives reflected radar signals and generates digital data encoding said received reflected radar signals, said antenna housed in a first housing and coupled by a cable to a counting and display unit housed in a second housing which is distinct from said first housing, said counting and display unit including a computer programmed to implement means for receiving said digital data transmitted from said antenna unit via said cable and performing at least one Fast Fourier Transform calculation on a plurality of said digital data and for calculating the true power of received reflected radar signals that are candidates for calculation of patrol car speed, strongest target speed or fastest target speed and using said true power information to improve the process of selection of candidate signals from which any of these speeds is to be calculated by suppressing weak signals and the effects of harmonics and intermodulation products.

21. The apparatus of claim 20 wherein said computer is programmed to implement means for selecting a spectral component for calculation of said patrol speed and, after calculation of patrol speed, for eliminating said spectral component used to calculate patrol speed from said spectrum of spectral components generated by said Fast Fourier Transform calculation by implementing a digital filter having a zero centered on the frequency of said spectral component from which said patrol speed was calculated and passing said spectral components through said digital filter to generate a new spectrum of spectral components, and using said new spectrum of spectral components for the process of selection of candidates for calculation of said strongest target speed and said fastest target speed.

22. A method for sending frame synchronization data in a data stream sent from a source to a destination along a cable, comprising:

sending digitized data from a source to a destination along one or more conductors of a cable, said digitized data having a plurality of bits arranged into frames having boundaries, each said bit contained within a bit interval marked by bit boundaries, said frame boundaries and said bit boundaries synchronized to a clock signal;

sending said clock signal from said source to said destination on a conductor of said cable, said clock signal having transitions marking the timing of said bit boundaries and said frame boundaries;

indicating to circuitry at said destination when each said frame boundary occurs by creating in said clock signal a blackout period by deleting several clock transitions marking bit boundaries immediately preceding said frame boundary, and sending a clock transition to said destination at the end of said blackout period.