Note: Descriptions are shown in the official language in which they were submitted.
8~
TRAFFIC RADAR SYSTEM
This invention relates to a radar system and more
particularly to a radar system usable for traffic patrol and
other applications with which the speed of a target vehicle
or other moving target structure can be measured from a
moving road patrol vehicle or other platform structure with
a high degree of accuracy and reliability.
Back~round of the Invention
Radar systems have heretofore been developed for
measuring the speed of a target vehicle from a moving road
patrol vehlcle. In one type of system, two doppler signal
components are developed, one being a reference signal
component developed in response to reflections from the
surface of a roadway or other stationary objects and the
other being developed from reflections from a moving vehicle.
; By comparing ~he frequencies of the two doppler signal
components, the speed of the moving target vehicle relative
to khe road surface can be determined. Such systems have
been generally satisfactory in operation. However, there
is a possibility that anomalies may be produced under cer~
tain conditions which, although unlikely to occurt have
made it possible to challenge the absolute reliability or
accuracy of indications obtained. For example, the reference
signal component, which should be produced from reflections
from the roadway to indicate ~he patrol car speed might be
produced from other moving vehicles in the radar beam.
There is also the possibility that false indications might
be produced after double reflections from elements of a
bridge or other structure.
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In the prior art, little if any consideration
has been given to possible alternatives which might avoid
such objections and if consideration is given to possible
alternatives, it will be found that they are such as to
apparently operate in a manner such as to be even more
objectionable. For example, if consideration is yiven
to the development of a reference signal from the speed
of rotation of the wheels of the patrol vehicle, it would
appear that such a reference signal would be affected by
the degree of inflation of the tires of the vehicle and
might produce large inaccuracies.
~ Summar ~ ention
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This invention was evolved with the general object
of overcoming the disadvantages of prior systems and of
providing a system with which the speed of travel of a
~, 20 moving target structure may be accurately and reliably
measured from a moving platform structure.
In accordance with this invention, a system is
provided in which a signal developed by radar means from
reflections from a moving target structure is compared with
a reference signal corresponding to the speed of a platform
structure in a manner such as to indicate the speed of the
`~ target structure relative to stationary objects. The reference
`~ signal is developed independently of the radar means and in a
system designed for a road patrol vehicle, for example, the
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eference signal may correspond to the rotational speed
of a wheel of the patrol vehicle and may be developed
from a device connected to the speedometer shaft or
associated therewith.
Such a reference signal might not accurately
indicate the actual speed of the platform structure and, in
accordance with the invention, calibration adjustment means
are associated with the reference signal developing means to
adjust the relationship between the reference signal and the
speed of movement of the platform structure. In a sys.em in
which the reference signal is developed from a vehicle wheel,
the relationship of the xeference signal to the rotational
speed of the patrol vehicle wheel is adjusted to obtain an
accurate relationship between the reference signal and the
actual speed of movement of the patrol vehicle relative to
the roadway.
With this arrangement, an accurate and reliable
measurement of the speed of a target structure can be
obtained without using the radar apparatus to measure the
platform structure speed during measurement of the target
structure speed so as to obviate false indications.
` ~ However, in accordance with a specific feature
of the invention, ~he signal produced by the radar means
and from reflections from the roadway and other stationary
objects is used for calibration purposes and removes any
anomalies that may be contained in the reference signal.
The radar proauced signal and the reference signal are
compared during calibration and calibration adjustment is
obtained by adjusting the reference signal to obtain sub-
`~ 30 stantial equality with the radar produced signal. Calibra-
--- tion can be perEormed under carefully controlled conditions
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since the radar system can detect moving targets, and the
possibility of any error from moving targets and other
anomalies is substantially obviated.
In accordance with another specific feature, the
indicator which is used under normal conditions for indi-
cating the speed of a moving target vehicle can be used
~ as an indicator of the radar produced signal during cali-
; bration. The other indicator which is used to indicate
the speed of the patrol car remains the same under both
normal and calibration conditions.
In accordance with a further specific feature of
the invention, the reference signal is developed through the
use of a phase-locked loop arrangement from a periodic signal
which is developed by a suitable transducer device and which
has a frequency varying as a function of the speed of the
platform structure. The transducer device may, for example,
be coupled to a speedometer shaft of a patrol vehicle. The
reference signal may, for example, be developed through a
frequency divider circuit from a voltage-controlled oscil-
lator of the phase-locked loop. To obtain a calibration
~ adjustment, the division ratio of a divider of the phase-
; locked loop or the division ratio of the divider circuit
used to develop the reference signal is adjusted. These
features have important advantages in that an accurate
calibration adjustment can be obtained while also generating
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a reference signal which can be compared with a periodic
signal to permit comparison by digital circuitry and to
provide a digital read-out.
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Additional features of the invention relate to
the provision of means for inhibiting the development of
signals which might produce inaccurate results and for
preventing the development of an output indication under
conditions in which inaccurate results could be obtained.
This invention contemplates other objects, fea-
tures and advantages which will become more fully apparent
from the following detailed description taken in conjunction
; with the accompanying drawings.
Brief Description of the Drawings
FIG. 1 is a schematic view illustrating patrol
and target vehicles on a roadway with a radar instrument
of the invention on the patrol vehicle;
.
FIG. 2 is a schematic block diagram of cir-
cuitry of the radar instrument of the invention; and
FIG. 3 is a schematic diagram showing details
of a conversion circuit included in the circuitry of
Figure 2.
` Description of A Preferred Embodiment
:
~; 20 Reference numeral 10 generally designates a radar
instrument constructed in accordance with the principles
of the invention. The instrument 10 as illustrated herein
is designed for use by police for the patrol of traffic but
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it will be understood that it can be used in any application
in which i~ is desired to measure the speed of a target str~c-
ture from a platform structure while both structures are in
motion relative to stationary objects. It is also noted
that in the preferred embodiment as illustrated herein, the
invention is advantageously applied to a radar instrument
having one particular type of circuitry and it will be
~ understood that basic concepts of the invention can be
; applied to instruments having various other types of cir-
cuitry. Specific examples as to circuit components and
arrangements and as to spee~s, frequencies, division ratios
and other numerical values are provided as illustrative
examples and are not to be construed as limitations.
As diagrammatically shown in Figure 1, the instru-
ment 10 may be mounted on a patrol vehicle 11 and includes
radar means for transmitting a signal toward a target vehicle
12 when the patrol vehicle and target vehicles are moving in
opposite directions on a roadway 13. Thus, the high frequency
energy may be txansmitted toward the targe~ vehicle 12 along
a path as indicated by reference numeral 14 to be reflected
back along the same path. By measuring changes in the trans-
mitted frequency, the relative speed of the two vehicles can
be measured. Changes in the transmitted frequency may be
conveniently measured by measuring only the difference
between the frequency transmitted and the frequency received.
Referring to Figure 2, reference numeral 15
generally indicates a microwave antenna and transceiver
unit for developing a doppler effect output signal having
a frequency proportional to speed. The doppler signal so
developed is applied through a tunable high pass filter
16 to a target phase detector 17 which controls a target
.
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voltage controlled oscillator 18. A second input of the
target phase detector 17 is connected to the output of a
divider circuit 20 having an input connected to the target
voltage controlled oscillator 18. The target phase detector
17 compares the signals applied thereto and so controls the
oscillator 18 as to maintain the frequency of the oscillator
at a certain multiple of the applied input doppler signal
: according to the division ratio of the divider 20. By way of
example, the division ratio may be 48 and the oscillator 18
may operate at a frequency of 48 times the incoming doppler
signal.
The frequency of operation of the oscillator 18
is proportional to the algebraic sum of speeds of the patrol
and taryet vehicles 11 and i2 and it is necessary to make a
comparison with a signal proportional to the speed of the
patrol vehicle in order to establish the absolute speed of
: the target vehicle relative to the roadwayO For this purpose
and to develop signals for display of both of the speeds, a
counter circuit 21 is provided which includes subtracter
~: 20 circuitry. A signal is applied through a line 22 from the
divider circuit 20 to the counter cir~uit 21. In addition,
a signal is applied through a line 23 from a conversion
circuit 24, the signal on line 23 being a function of the
~: speed of movement of the patxol vehicle 11. Outputs of the
counter circuit 21 are applied to patrol and target display
units 25 and 26 for digital display of the respective speeds
of the two vehiclesO
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The construction of the counter circuit 21 is
~` such that the frequency of the applied signals may be equal
to six times the frequency of the corresponding doppler
signal which may be 31.389 Hz/MPH by way of example and
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not by way of limitation. Thus, the frequency on the line
22 may be 188.334 Hz/MPH and with a division ratio of 48
between the frequency of the oscillator 18 and the doppler
frequency, the line 22 may be ~aken from a tap on the
divider circuit 20 at which a division ratio of 8 is
obtained.
The signal on line 23 would then be at a fre-
quency of six times the frequency of a signal generated
at the rate of 31.389 HZ per ~H of the patrol vehicle and
may be designated as a "6X" signal. The converslon circuit
24 additionally develops a "48X" output signal at a frequency
equal to eight times the frequency of the signal on line 23,
the signal being applied through a line 28 ~o the program-
mable notch filter 16. In response to the signal so applied,
the tunable high pass filter 16 filters out signals at
frequencies within a narrow band centered on the frequency
of 31.389 Hz/MPH of the patrol vehicle. The result is that
during normal operation, the system is non-responsive to
signals derived from reflections from stationary objects.
The conversion circuit 24 also develops signals
for limiting the range of a sweep operation of the voltage-
controlled oscillator and for preventing the development
~ of indications from multiple reflections.
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The voltage controlled oscillator 18 may preer-
ably be so designed as to automatically sweep or change its
frequency through a certain frequency range when no target
~ehicle is within range and to automatically lock in and
cause an indication to be produced when a reflection from
a target vehicle is received, under control of the phase
detec~or circuit 17. When ~he locking function is per-
formed, a lock signal may be developed at an output line
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29 of the phase detector, which may be applied through a
gate 30 and a line 31 to a target lock input of the
counter circuit 21. The gate circuit 30 is controlled
through a line 32 from an output of a harmonic detector
circuit 34 which has one input connected to the output
of the oscillator 18 and a second input connected through
a line 36 to an output of the conversion circuit 24.
The purpose of the gate circui~ 30 and the har-
monic detector circuit 34 is to prevent obtaining of
improper readings in response to multiple bounce or multiple
reflections which might be produced, for example, when the
patrol vehicle is approaching a bridge or other strongly
reflecting structure. When, for example, the patrol
vehicle is moving at 50 MPH and is approaching a bridge,
there is a posslbility of a signal being developed from a
double reflection which corresponds to a closing speed of
100 MPH. If there is a substantial angle between the
direction of movement of a patrol vehicle and the line to
the reflecting surface, there is a cosine error which might
extend the frequency range of the received double reflected
signal to say, from 98 to 102 MPH. The harmonic detector
; 34 is arranged to detect such signals.
For proper operation, the signal applied through
the line 36 to the detector 34 should be at a sub-multiple
of the oscillator output frequency and may preferably be a
"12X" signal at a frequency equal to 1/3 the oscillator
frequency~ assuming that the oscillator frequency is 48
times the doppler frequency.
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It i~ also desirable to limit the frequency range
throu~h which the oscillator 18 sweeps when no reflection
from a target is being received. In the system as illus-
trated, a signal is applied from the conversion circuit 34
and through a line 38 to the oscillator circuit 18, to
limit the low end of the search range to a frequency slightly
above the frequency which corresponds to the speed of
movement of the patrol vehicle. For example, with the
patrol vehicle traveling at 50 MPH, the signal on line 38
may prevent the voltage controlled oscillator 18 from
sweeping below a frequency which corresponds to about 51
MPH.
The conversion circuit thus operates to supply a
"6X" output signal on line 23 for applying th~ patrol
speed signal to the counter circuit 21, a 48 output on
~ line 28 for control of the high pass filter 16, a 12X output
; signal on line 36 for application to the harmonic detector
34 and a DC voltage on line 38 to limit the lower end of
the sweep range of the voltage control oscillator 18.
The conversion circuit 24 develops such signals
from an input signal applied through a line 39 from the
output of an odometer module 40 which, as diagrammatically
indicated by line ~1, may be coupled to a wheel 42 having a
tire 43. The odometer module 40 may, for example, be coupled
to the conventional shaft on the transmission of the vehicle,
or any part of the vehicle that has movement proportioned to
the rotational speed of the drive wheels of the vehicle. The
~ coupling may be a mechanical, magnetic or electxonic
;~ device. The coupling may be the receipt o~ an electronic
signal from an electronic odometer.
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The output signal of the odometer module may
preferably be in the form of a wave or other periodic
signal having a frequency proportional to the rotational
speed of the wheel 42. For example, the odometer module
may generate a square wave having 6,000 pulses per mile so
as to produce an output frequency of 1.6667 Hz/MPH, assuming
a certain effective wheel diameter such as produced with
average, normal inflation of the tires and assuming that
other conditions are normal. The relationship between the
; 10 frequency of the signal on line 39 and the actual speed of
movement of the patrol vehicle may change very substantially
with changes in the inflation of the tires, temperature,
etc., and an important feature of the invention relates
to the provision of means for making calibration adjust-
ments of the conversion circuit 24.
Calibration can be performed either automatically
or manually and in either case should be per~ormed when
there are no vehicles in range of the radar. In automatic
calibration which may be performed at timed intervals, the
absence of vehicles in range of the radar may be signaled to
the conversion circuit through line 29 and the conversion
circuit may then deactivate the filter 16 through the line
28 and remove the sweep limit signal applied through line 38
so as to allow the voltage controlled oscillator 18 to lock
2S in on the return signal from the roadway. The conversion
circuit 24 may then adjust the 6X signal on line 23 until
the signal on line 23 is effectively equal to that on line
22.
.
For manual calibration, a swi ch control 45 is
moved from a normal position as illustrated ~o a calibrate
position in which a switch 46 is closed. A signal is then
applied from a terminal 47 to lines 4B, 49 and 50 to deacti-
vate the filter 16, remove the sweep limit of the oscillator
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18 and deactivate a subtractor portion of the circuit 21.
The conversion circuit 24 may then be adjusted through a
pair of thumb wheel switches 51 and 52 until the two
displayed speeds match. It will be understood that
potentiometers, switches or other devices may be used
for calibration in place of the thumb wheel switches 51
and 52.
Once the system is calibrated, it will track
while operating over a wide range of speeds, as from 100
MPH down to 1 MPH. For the automatic calibration operation,
a signal may be developed periodical]y within the conversion
circuit 24 or from an external source to cause the calibration
to be performed at timed intervals.
Figure 3 is a circuit diagram of a form of the
conversion circuit 24 designed for the manual calibration
operation as above described. It will be understood that
the circuitry is shown in detail to provide an illustrative
example and other types of circuitry may be used. In the
circuit of Figure 3, the signal from the odometer module 40
is applied through the line 39 to a Schmitt trigger circuit
54 including a diode 55 between line 39 and a circuit
point 56 which is connected through a resistor 57 to a
power supply terminal 58 and also to the input of an
inverter 59. The Schmitt trigger circuit converts the
input signal to the proper level fox the circuitry which
may preferably be of a Cmos type. The Schmitt trigger
circuit 54 also eliminates input noise.
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The output of the Schmitt trigger circuit 54, at
the output of the inverter 59, is applied to one input of a
~ phase-locked loop circui~ 60 which has a second input con-
I nected to the output of a programmable divider circuit 62.
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A clock input of the programmable divider circuit 62 is
connected to a voltage controlled oscillator output line
63 from the loop circuit 60. The line 63 is connected to
one input of a gate circuit 64 which has an output con-
nected to a clock input of a fixed divider circuit 65.
Outputs of the fixed divider circuit 65 are connected to
inputs of a gate 66 which has an output connected to a
; second input of the gate 64 and also to an enable input of
the programmable divider 62.
10The divider 65 together with the gates 64 and 66
operates to count to 132, then disables itself while
enabling the programmable divider 62. When the count in
the divider 62 equals a proyrammed count of from zero
to 39, both counters 62 and 65 are reset and the process
; 15is restarted. The pxogrammable divider 62 is controlled
from the thumb wheel switches 51 and 52 and a BCD code may
be used. The switch 51 controls the "tens" digit through
a "10" line and a "20" lineO The switch 52 controls the
~`units digit through "1", "2", "4" and "8" lines. Thus, the
division ratio of the phase-locked loop may be adjusted
from 132 to 171.
The output of the phase-locked loop circuit 60
at line 63 is applied to one input of another phase-locked
loop circuit 68 which has a second input connected to the
~5 output of a fixed divider circuit 69 having an input con-
nected through a line 70 to a voltage controlled oscillator
output terminal of the phase-locked loop 68. The divider
69 has a division ratio of 6 and thus ~he ou~put signal at
line 70 has a frequency equal to 6 times the frequency of
the signal at line 63. Accordingly, the signal at line 70
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has a frequency equal to from 792 to 1026 times the input
frequency on line 39, depending upon the adjustment of the
thumb wheel switches.
If it is assumed that the input frequency at line
39 is 1.6667 Hz/MPH under typical or average conditions
with respect to tire inflation, etc., the desired multi-
plier factor is 904 to obtain a frequency equal to 48 times
the corresponding doppler frequency and with the arrangement
as described and shown, the desired multiplier of 904 is
~btained at abcut a mid-range switch setting.
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The following i.s a chart of the resultant fre-
quency multipliers produced by the fixed multipliers and
the programmable adjustment~ (Mult = (132 + thumbwheel
settiny) X 6.
5 Sw. Mult. Sw. Mult. Sw. Mult. Sw. Mult.
_
0 792 10 852 20 912 30972
1 798 11 85~ 21 918 31978
2 804 12 86~ ~2 924 32984
3 810 13 873 23 930 33990
4 816 14 87~ 24 936 34996
S 822 lS 882 25 942 351002
6 828 16 888 26 94~ 361008
7 834 17 89~ 27 954 371~14
8 840 18 900 28 960 381020
: 15 9 846 19 906 29 966 391026
As specified earlier, the desired multiplier is
904 if the odometer reading is exactly 1.6666 Hz/MPH.
This yields an adjustment range of ~ 13.49~ to - 12.38~,
in .648% increments. Total error, due to step size, is
then .324%.
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The accuracy thus obtained is more than adequate
or most applications. However, if greater accuracy is
desired, it may be readily obtained by incxeasing the fre-
quency of operation of the voltage controlled oscillators
: 25 of the phase-locked loops while also increasing the number
of divider stages.
The output of the phase-locked loop 68 at line 70
is applied directly through the line 28 to th0 programmable
notch filter 16 and is also applied to the input of a fixed
divider circuit 72 which has a divide-by-4 output connected
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to the 12X output line and a divide-by-8 output connected
to the 6X output line 23.
To develop the DC signal on line 38, for limiting
the frequency range of sweeping of the voltage controlled
oscillator 18, a frequency-to-voltage converter 73 is pro-
vided having an input connected to the output line 63 from
the phase-locked loop 60 and having an output connected to
a subtracter and buffer amplifier 7~, the output of ampli-
fier 74 being connected to the line 38. The circuits 73
and 74 operate to develop a DC voltage of the proper mag-
nitude for limiting the lower end of the sweep frequency
range. By way of example, it may provide a DC voltage on
line 38 of from + S volts to + 2.5 volts in 0.025 volt
increments. Thus, at 1 MPH, the voltage may be 4.975 volts
and at lO0 MPH, the voltage may be 2.5 volts.
The conversion circuit thus operates to generate
the required signals for application to the counter circuit
21, the tunable filter 16, the voltage control oscillator 18
and the harmonic phase detector 34 with a high degree of
accuracy. The use of the phase-locked loops in the conver-
sion circuit is an advantageous feature. It permits accurate
calibration adjustment through the use of the programmahle
di~ider 62, controlled by the thumbwheel switches 51 and
52. Also, the relationship between the frequency of the
output of the odometer module 40 and the speed of rotation
of the patrol ~ehicle wheels is not critical and different
relationships can be readily accommodated by adjustment or
selection of the ratios used in the dividers of the conver-
sion circuit.
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The radar instrument 10 together with the
odometer module 40 thus provides a system which includes
platform structure speed measuring means operable inde-
pendently of energy transmitting and receiving means for
developing a signal corresponding to the speed of the plat-
form structure relative to stationary objects, such platform
structure speed measuring means being formed in the illu-
strated system by the odometer module 40 operating in
conjunction with the conversion circuit 24, the signal
produced by such platform structure speed measuring means
being produced on the line 23. The signal so produced is
compared by the counter and subtracter circuit 21, in the
illustrated system, with a signal produced on line 22 by the
~ energy transmitting means and associated components, including
: 15 the unit 15, filter 16, phase detector 17 and voltage con-
trolled oscillator 18. The conversion circuit 24 in the
illustrated system further includes the programmable divider
62 and associated components which form calibration adjustment
means operable for insuring an accurate relation between the
signal on line 23 and the actual speed of movement of the
platform structure speed measuring means.
. An auxiliary platform structure speed measuring
1 means is provided in the illustrated system by the compo-
: nents operated when the switch 46 is closed. A signal is
then applied to deactivate the filter 46, remove the sweep
limit of the oscillator 18 and deactivate a subtracter
portion of the circuit 21, the conversion circuit 24 being
then adjustable through the thumbwheel switches 51 and 52 to
obtain a match between the two displayed speeds. The speed
` 30 of the platform structure as measured from the odometer
module 40 and associated circuitry is then again indicated
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on the patrol disp]ay 25 while the speed of the platform
structure as measured from the auxiliary platform structure
speed measuring means, then formed by the transmitter-
receiver unit 15 and associated circuitry, is indicated on
the target display 26. Thus, the target display 26 in the
illustrated system forms an indicating means which is
operable in a calibration mode of operation to indicate the
speed of the platform structure and which is operable in a
normal mode of operation to indicate the speed of a target
structure.
It is noted that the target structure speed
measuring means and the auxiliary platform structure speed
measuring means include common circuitry. The phase detector
~; 17, voltage controlled oscillator 18 and divider circuit 20
; 15 are selectively used in such means in the illustrated system,
the notch fil-ter 16 being disabled when such common circuitry
is used as auxiliary platform structure speed measuring
means.
The platform structure speed measuring means in
the illustrated system comprises a phase-locked loop 60
which includes a voltage controlled oscillator and a phase
detector, the phase-locked loop having two inputs. One of
such inputs in the illustrated system is connected to the
output of frequency divider means formed by the programmable
divider 62 and the fixed divider 65 in the illustrated
system, the other of the inputs being connected through the
inverter 59 and diode 55 to the output of the odometer
module 40 which forms transducer means developing an output
signal in response to movement of the platform structure.
Frequency divider means including the phase-locked loop 68,
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fixed divider 69 and fixed divider 72 are provided for
developing from the output of the oscillator of the phase-
locked loop 60 a signal proportional to the speed of move-
ment of the platform structure. It is noted that the
- 5 calibration adjustment means is associated with one of the
frequency divider means, such being the programmable divider
6~ in the illustrated system.
The circuitry of Figure 3 is designed for manual
calibration. For automatic calibration~ circuitry may be
added to adjust and obtain substantial equality between
signals such as those developed on lines 22 and 23 in
response to the signal on line 29 and an internally or
; externally generated timing signal.
The circuit is particularly designed for the
illustrated radar system in which a phase-locked loop is
used for generating the signal for application to the
` counter circuit 21 to operate the target display 26 after
digital subtraction of the patrol vehicle speed signal.
However, the conversion circuit 24 could be readily adapted
for use in radar systems having other types of circuitry~
~ It will be understood that one particular type
- of system is disclosed herein to facilitate an understanding
of the concepts of the invention and to provide an example
of a preferred embodiment and other types of systems might
be used in accordance with the invention. For example, the
use of phase-locked loops is advantageous in many respects
but other forms of circuitry might be used to receive
doppler effect signals and convert them to displayed
readings. The use of a tachometer type of odometer module
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is also advantageous but the odometer module may have other
forms and might develop current, voltage, electronic data or
frequencies as the output. The calibration procedure may be
performed automatically as well as manually, as above noted.
It will be understood that other modifications and
variations may be effected without departing from the spirit
and scope of the novel concepts of this invention.
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