INVESTIGATION PERTAINING TO ELIMINATION OF AMBIGUITIES DUE TO HIGH PULSE REPETITION RATES FINAL REPORT

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP81-01043R002900240002-8
• Release Decision: RIPPUB
• Original Classification: K
• Document Page Count: 130
• Document Creation Date: December 23, 2016
• Document Release Date: January 31, 2014
• Sequence Number: 2
• Publication Date: May 1, 1956
• Content Type: REPORT

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STAT
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STAT \
INVESTIGATION?PRRTAINING
ELIMINATION OF AMBIGUITIES DUE TO
HIGH PULSE REPETITION RATES
FINAL REPORT
December 1, 1953 - May 1, 1956
0.7e,
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Signal Corps Contract
No. DA-36-039 0C-56696
Department of the Army Project
No. 3-99-05-022
Signal Corps Project
No. 122B
U.S. Army
Signal Corps Engineering Laboratories
Fort Monmouth, New Jersey
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INVESTIGATION PERTAINING TO
ELIMINATION OF AMBIGUITIES DUE TO
HIGH PULSE REPETITION RATES
Signal Corps Contract
No. DA-36-039 SC-56696
A.Ze-Xte4t
,
s'gf:6
U.S. Army
Signal Corps Engineering Laboratories
Fort Monmouth, New Jersey
Itr?rtr?c.4
Pw4-1
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STAT
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INVESTIGATION PERTAINING TO
ELIMINATION OF AMBIGUITIES DUE TO
HIGH PULSE REPETITION RATES
FINAL REPORT
December 1, 1953 - May 1, 1956
OBJECT
The object of this development is to
obtain a design for a piece of equipment
which, when either integrated into new radars,
or applied to existing ones, shall enhance the
performance of the radar by increasing the
number of target "hits" per scan beyond the
limit normally set by Maximum unambiguous range.
Signal Corps Contract No. DA-36-039 SC-56696
Signal Corps Technical Requirements
No. SCL-2803, 30 July 1953
Amendment No. 1, 6 December 1954
Department of the Army Project No. 3-99-05-022
Signal Corps Project No. 122-B
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II
*
TABLE OF CONTENTS
LIST OF FIGURES
GLOSSARY OF SYMBOLS
II PURPOSE
III ABSTRACT
IV PUBLICATIONS, LECTURES, REPORTS
AND CONFERENCES
V FACTUAL DATA
INTRODUCTION
Page
iii
vi
xi
1
3
7
9
METHODS FOR DISCRIMINATING 15
FALSE RANGE INDICATING ECHOES
METHODS FOR SUPPRESSING DISCRIMINATED 29
FALSE RANGE INDICATING ECHOES AND
RANDOM NOISE
DESCRIPTION OF EXPERIMENTAL EQUIPMENT
Introduction 39
PIM Radar Simulator 43
Optical-Electronic 57
Ambiguity Filter
Storage-Tube Ambiguity Filter 89
Power Supplies and Regulators 105
TRANSIENT RESPONSE OF PHOSPHORS
Theoretical Derivation 117
Experimental Verification 139
OPTICAL-ELECTRONIC AMBIGUITY 157
FILTER SUBRANGE COMBINING SYSTEM
STORAGE-TUBE AMBIGUITY FILTER 163
MAGNETIC-STORAGE AMBIGUITY FILTER 207
iii
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CONCLUSIONS
OVERALL CONCLUSIONS
RECOMMENDATIONS
Page
227
229
233
iv
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List of Figures
No. Title 122-0-
?
1
2
3
Methods for Discriminating False Range
Indicating Echoep
Methods for Suppressing Discriminated
False Range Indidating Echoes
PIM Experimental Equipment - Photograph
12
13
40
4
Rear Views of PIM Equipment Racks -
41
Photograph
5
PIM Radar Simulator - Block Diagram
44
6
PIM Modulator - Block Diagram
46
7
PIM Modulator - Schematic Diagram
47
8
PIM Modulator - Photograph
48
9
Artificial Echo Unit - Block Diagram
50
10
Artificial Echo Unit - Schematic Diagram
51
?
11
Artificial Echo Unit - Photograph
52
12
Noise and Echo Mixer - Schematic Diagram
55
13
Noise and Echo Mixer - Photograph
56
14
Optical-Electronic Ambiguity Filter
58
System - Block Diagram
15
Optical-Electronic Ambiguity Filter
60
Subrange Combining System - Block Diagram
16
5 Channel Oscilloscope - Block Diagram
62
17
5 Channel Oscilloscope - Beam Blanking
64
Amplifier and High Voltage Divider -
Schematic Diagram
18
5 Channel Oscilloscope - Horizontal Sweep
65
Amplifier - Schematic Diagram
19
5 Channel Oscilloscope - Vertical Position-
66
?
ing Circuit - Schematic Diagram
20
5 Channel Oscilloscope - Photograph
67
21
Staircase Voltage Generator - Block Diagram
70
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No.
Title
22 Staircase Voltage Generator - Input Pulse 71
AMplifiers, Triggers No. 1 and Reset
Amplifier - Schematic Diagram
23 Staircase Voltage Generator - Delay and
Gate No. 1, Output Cathode Follower No. 1,
and Sync. Output Amplifier - Schematic
Diagram
24 Staircase Voltage Generator - Reset One-
Shot Multivibrator and Reset Amplifier -
Schematic Diagram
25 Staircase Voltage Generator - "Number-of- 74
Steps" Switch and Voltage Divider - SchemP'-
atic Diagram
26 Staircase Voltage Generator - Photograph
27
72
73
Vertical Deflection Amplifier - Block
Diagram
28 Vertical Deflection Amplifier - Schematic
Diagram
29 Vertical Deflection Amplifier - Photograph
30 Horizontal Deflection Amplifier - Block
Diagram
31 Horizontal Deflection Amplifier - Schematic 86
Diagram
77
80
81
83
85
32 Horizontal Deflection Amplifier :Photograph 87
90
33 Storage Tube Ambiguity Filter System,
DifIection-Modulation, Base-Line-Scanning -
Block Diagram
34 Storage Tube Ambiguity Filter System,
Negative-Intensity-Modulation, Base-Line-
Scanning - Block Diagram
35 Gate Generator - Block Diagram
36 Gate Generator - Schematic Diagram
37 Write Amplifier - Block Diagram
38 Write Amplifier - Schematic Diagram
39 Potential Shifter - Block Diagram
vii
91
93
94
96
97
99
No.
Title
Page
40
Potential Shifter - Schematic Diagram
100
41
315 Tektronix Scope with Radechon Tube -
102
Block Diagram
?
42
Storage Tube Unit - Photograph
103
a
43
D.C. Voltage Regulator Plug-in Unit
106
Schematic Diagram
44
D.C. Voltage Regulator for Positive Voltage
107
Operation - Schematic Diagram
45
D.C. Voltage Regulator for Negative Voltage
108
Operation - Schematic Diagram
46
D.C. Voltage Regulator - Photograph
109
47
High Voltage Power Supply - Schematic Diagram
110
48
High Voltage Power Supply - Photograph
111
49
Dual D.C. Power Supply - Schematic Diagram
112
50
Dual D.C. Power Supply - Photograph
113
51
Potential Shifter Ripple Filter Chassis -
115
I
lb
Schematic Diagram
52
Spectral Sensitivity of Average Human Eye,
6198 Vidicon Tube, and Photomultiplier with
129
SA Response -
53
Relative Spectral Energy Distribution of
140
Pl, P2, and Pll Phosphors and 54 Spectral
Sensitivity Distribution
54
Equipment to Measure Transient Brightness
142
Variation in CRT Phosphors - Block Diagram
55
Photomultiplier Circuit - Schematic Diagram
144
56
Normalized Brightness Build-up and Decay
in Type P1 Phosphor
146
57
Normalized Brightness Build-up and Decay
in Type P1 Phosphor
147
a
V
58
Normalized Brightness Build-up and Decay
in Type P2 Phosphor
150
59
Normalized Brightness Build-up and Decay
in Type Pll Phosphor
152
viii
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No.
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
Title
Optical-Electronic Ambiguity Filter,
Deflection-Modulation, Base-line Break
Detection - Oscillogram
Optical-Electronic Ambiguity Filter,
Deflection-Modulation, Base-line Break
Detection - Oscillogram
Relative Charge Density on Target After
Three Sweeps by Electron Beam Writing
Echo Information
Simplified Radechon Storage-Tube Circuit
Radechon Characteristics
Radechon Characteristics
Target Charging Characteristics
Storage-Tube Output Signal
Theoretically Determined Ambiguity
Suppression Figure-of-Merit
Theoretically Determined Ambiguity
Suppression Figure-of-Merit
Theoretical Minimum Relative Charging
Voltage for Infinite Ambiguity Suppression
Theoretical Minimum Cumulative Relative
Writing Beam Current for Infinite Ambiguity
Suppression
Theoretical Minimum Cumulative Relative
Writing Beam Current for Infinite Ambiguity
Suppression
Storage-Tube Ambiguity Filter Experimental
Ambiguity Suppression Figure-of-Mei
Storage-Tube Ambiguity Filter Experimental
Noise-Suppression Figure-of-Merit
Storage-Tube Ambigulty Filter Experimental
Ambiguity Supprengion Figure-of-Merit
Storage-Tube Ambiguity Filter Experimental
Noise-Suppre:11Jion Figure-of-Merit
Storage-Tube Amblqujt7 Filter Operation,
Deflection-MrAulti, f;.911ne Break
Detection -
Page
158'
159
166
171
176
177
179
183
185
186
189
190
191
196
197
198
199
200
?
1
No.
Title
Page
78
79
80
81
82
83
84
Storage-Tube Ambiguity Filter Operation,
Deflection-Modulcation, Baseline Break
Detection - Oscillogram
Storage-Tube Ambiguity Filter Operation,
Negative-Intensity-Modulation, Baseline
Break Detection - Oscillogram
Storage-Tube Ambiguity Filter Operation,
Negative-Intensity-Modulation, Baseline
Break Detection - Oscillogram
Series-Read Magnetic-Storage Ambiguity
Filter System - Block Diagram
Operation of Series-Read Magnetic-Storage
Ambiguity Filter System
Series-Write Magnetic-Storage Ambiguity
Filter System - Block Diagram
Normalized Amplitude and Phase Shift of
Double Time Averaged Sinusoidal Signal
201
202
203
209
212
214
219
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-"T
A63.-
'at
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A
?
?
Bi
Cx
CRT
fs
AS
FNS
FRI
HTA
bR
IbW
Is
IsR
bR
JbW
GLOSSARY OF SYMBOLS
Mea2iaa Page of First
Appearance
amplitude of input signal
effective brightness
effective brightness due to i
type luminescent-centers
initial value of B.
saturation effective brightness
due to i type luminescent-centers
speed of light
target capacitance per unit area
abbreviation for "cathode ray tube'
frequency
maximum unambiguous repetition rate
repetition rate
ambiguity suppression figure-of-merit
noise suppression figure-of-merit
abbreviation for "false range
indicating'
Planck's constant
abbreviation for 'higher time around"
electron beam current during read
operation
electron beam current
operation
signal current
signal current diring
relative beam current
operation
relative beam current
operation
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xi
during write
read operation
during read
during write
217
130
130
130
136
222
172
30
120
221
223
al
10
9
120
9
175
172
173
174
174
172
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cZa
Symbol
JsR
PCI
Pdi
Pei
Pet
pfi(f)
Meaning
relative signal current during
read operation
Additional subscripts have
the meanings?
B for the baseline
FRI for a FRI echo
TRI for a TRI echo
constant of proportionality
number of intervals in a PIM
modulation cycle
number of transition-electrons in
the conduction-band per unit area
of the CRT screen
Page of First
Appearance
174
180
181
182
217
30
123
number of excited i type luminescent- 121
centers per unit area of the CRT
screen
initial value of N
el
number of i type luminescent
centers per unit area of the CRT
screen
number of transition-electrons in
the high-energy-electron traps per
unit area of the CRT screen
number of
number of
unit area
126
121
124
electrons in excess of the 125
holes in the phosphor per
of the CRT screen
probability time density that conduct-
ion-band electrons will drop to excited
iatype luminescent-centers
probability time density of decay of
i type luminescent-centers
probability time density of excitation
of i type luminescent-centers
probability time density that electrons
will escape from
traps
frequencyfrequency density of radiation from
the decay of i type luminescent-centers
xii
123
121
131
123
127
22shal.
Ptt
RM
Ro
s(f)
V
SN
Ta
T. .
lej
TM
Tw
TT
TRI
Meaning Page of First
/32222ESEEt_
probability time density that 123
conduction-band electrons will
become trapped in high-energy-
electron-traps
abbreviation for "pulse interval 15
modulation"
abbreviation for "pulse repetition 9
frequency'
abbreviation for "Quarterly Progress 16
Report"
barrier grid transmission ratio 172
maximum range of the radar 222
output load impedance 173
spectral sensitivity distribution 129
of Vidicon tube
voltage signal-to-noise ratio 195
time 125
averaging time interval 218
time interval between i and j 208
time length of the PIM modulation 210
cycle
averaging time interval during writing 216
averaging time interval during reading 216
abbreviation for "true range indica- 10
ting
speed 208
speed deviation 221
amplitude of random noise 10
scan speed during read operation 174
average secondary electron energy 172
in electron volts
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Symbol
Vtb
V
TB
vw
V
BQ
VFRI
V.
in
Vout
amp
V -
out
VTRI
xd
x.
1
xr
xw
a.
Meaning
target-to-barrier grid charging
voltage
Additional subscripts have
the meanings?
oW at start of write operation 172
nW after n write sweeps
OR at start of read operation 173
B for the baseline 180
FRI for a FRI echo 181
TRI for a TRI echo 182
IR after one read sweep 175
Page_ of First
22.S.2E2E9.1._
170
actual target-to-barrier grid voltage 170
scan speed during write operation
equilibrium target-to-barrir grid
voltage
amplitude da FRI echo
input signal
output signal
amplitude of output signal
amplitude of a TRI echo
head position deviation
head air-gap width
distance between heads
read-head air-gap width
write-head air-gap width
decay constant of i type
luminescent-centers
target secondary emission ratio
excitation constant of i type
luminescent-centers
wavelength
luminous power output per unit area
of the CRT screen
xiv
172
170
' 11
218
217
217
10
224
218
208
216
216
125
174
133
221
128
a
II PURPOSE
The purpose of this contract is to
continue the study and development of
techniques which will permit the use of
high pulse repetition rates in long range
radars and MTI radar without the range
ambiguities which normally are present as
the result of returns from "second-time-
around", "third-time-around" and "higher-
time-around" echoes.
1
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III. ABSTRACT
The performance of a radar, with respect to the
detection of weak target echoes and MTI operation, is
improved by increasing the pulse repetition frequency
(MU). A practical upper limit to the PRF is reached
when higher-time-around echoes cause ambiguous range
indications. Advantage can be taken of a high PRF if
the false-range-indicating (FRI) echoes can be dis-
criminated from the true-range-indicating (TRI) echoes.
The operation is further enhanced if the discriminated
FRI echoes are suppressed sufficiently so that they do
not clutter up the radar display. Methods for accomplish-
ing both the discrimination and the suppression of the
FRI echoes which also utilize the high PRF to improve
the signal-to-noise ratio (SN) have been devised in the
course of this research project.
Modulation of the time interval between successive
transmitter pulses produces a distinctly and readily
usable discrimination between TRI echoes and FRI echoes.
No suppression of the FRI echoes or random noise is
accomplished by the pulse interval modulation (PIM)
alone. Several ambiguity filters, which suppress the'l
FRI echoes and random noise, have been evolved for
use in the PIM System, based on optical-electronic,
electrostatic-storage, and magnetic-storage devices.
The Optical-Electronic Ambiguity Filter has been both
theoretically and experimentally investigated, and
3
7,I1W
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first crrder figares-of-merit have been determined. Pre
limy theoretical and experimental investigation of
the Storage-T-ibe Ambiguity Filter indicate potential
superior1.1-7 over mhe aptical-Electronic Ambiguity Filter
in ho::r1 i= 1d practicality, even though the
experimental figures-o=-merit obtained so far for the
Optica2-Electronic Arbiguity Filter exceed those for the
Storage-Tube Ambiguity Filter= The Magnetic-Storage
Ambi=u
7741+=r is first introduced in this report.
The first order determination of some of the important
system parameters and figures-of-merit indicates
substantial promise for this system, but no experimental
work has been done= A special point to note is that all
these ambic,,ity filters utilize their non-linear
characteristics to give ambiguity and random noise
_
suppression such greater than can be obtained by an
ideal linear integrator. The ambiguity suppression
ficvre-of-it (FAs) and the noise suppression
figure-of-merit (Flis) of an ideal linear integrator
are n and IT, respectively, where n is the number of
pulses integrated0
of the transmitter at several different
otlse repetition frequencies simultaneously (Mixed
PH.17; prodlIces a high net PRF and imparts the distinctive
Information to the signal necessary for discrimination
between TRI echoes and FRI echoes, Periodic filters
(comb filters) perform the actual discrimination
between TRI echoes and FRI echoes and also suppress
4
?
the FRI echoes and random noise. The Comb-Type Ambiguity
Filter, for use in the Mixed PRF System, has been given
preliminary theoretical investigation but no experimental
work has been done.
Two special items considered during the last quarter
of the project, in conjunction with the Optical
Electronic Ambiguity Filter, were the transient response
of CRT phosphors and the subrange combining system.
General equations for the transient brightness build-up
and decay in a phosphor were formulated. Assumptions
applicable to the special conditions of usage in the
Optical-Electronic Ambiguity Filter were used to
simplify the form of the equations and a preliminary
experimental verification of results derived from
these equations was made. The first three subrange
displays of the echo information presented by the
Optical-Electronic Ambiguity Filter were successfully
combined into a single continuous range display. The
extension of this system to more subranges is possible
by the addition of duplicate system components.
5
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IV PUBLICATIONS, LECTURES, REPORTS AND CONFERENCES
A. Publications No publications resulted from the
project during the eighth quarter.
B. Lecturesg
Title Lecturer Place Date
"Transient H. M. Musal Illinois 24 Feb-
Behavior of Institute ruary 1956
Phosphors" of Tech-
nology
C. Reportss
Ref. No. Title Author Date
21 Monthly Per- G.I. Cohn November,
formance 1955
Summary
22 Monthly Per- G.I. Cohn December,
formance 1955
Summary
6095-35 Optical- H. M. Musal March,
Electronic 1956
f ?
Ambiguity Filter
Subrange Combin-
ing System
6095-36 Storage-Tube H.M. Musal April,
Ambiguity 1956
Filter
6095-44
Magnetic-
Storage
Ambiguity
Filter
6095-45 Transient
Response of
Phosphors
H.M. Musal April,.
1956
H.M. Musal February,
1956
6095-46 Experimental R.F. Purnell April
Equipment for 1956
PIM System and
Ambiguity Filters
D. Conferencesg
No conferences were held in connection with the
project during the eighth quarter.,
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V FACTUAL DATA
INTRODUCTION
Statement of Problem
The performance of a radar system is directly dependent
on the signal to noise ratio. Signal integration is one
method of improving the signal to noise ratio. The higher
the pulse repetition rate (PRF), the greater the amount of
integration possible, and consequently, the larger the
signal to noise ratio. Signal to noise ratio improvement
with high PRF's is possible when the noise is completely
random, and also when the
as echoes from stationary
noise is an undesired signal such
or slowly moving targets, i.e.,
clutter. For example, in MTI radars
improves pulse to pulse cancellation
stationary and slowly moving targets
ratio of desired signal (response to
undesired signal (clutter).
If the distance to a target is such that the echo due
to a given transmitter pulse does not return to the radar
prior to the transmission of one or more subsequent pulses,
the echoes are called higher-time-around (HTA) echoes. The
detected HTA echoes can produce as many different false
range indicating (FRI) echoes on the radar indicator as
there are transmitter pulses radiated between tbg one caus-
ing the echo and the return of an echo from a target at
maximum range. As the PRF is raised to improve the signal
to noise ratio, the number of HTA detectable echoes is
an increase in PRF
of echoes from
thereby increasing the
moving targets) to
9
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increased from none to many. Since there is an additional
range indication for each detectable HTA echo, the range
display is ambiguous unless some means is introduced for
identifying which of the many range indications is the
true one.
The presence of the multiple range indications for each
target quickly clutters up the indicator display, especially
when more than a few targets are present, even with the true
ra,n0e indicating (TRI) echoes differentiated from the FRI
echoes. consequently, it is highly desirable to devise
means not only of distinguishing the TRI echoes, but also
of eliminating the FRI echoes from the display.
In -order to compare the relative performance capabilities
zwtems, it is necessary to determine the
flgure f merit cf each system. The noise suppression
meritThz-- a system is taken as :
..L1.7:ure
where VIIRT is
rr.'s amplits.tde
VTR7
7.-; out
'TRI
Xrmisi in
the amplitude of a VI echo, and VNrms
For a larger figure of
is =re sensitive, i.e., smaller and more
t4t.A.C.*
tax;e:s are detectable.
the PRF increases the radar figure of merit
at
expense of introducing FRI echoes. Once the FRI
haTe been '41scriminated, they play the same undosir-
of the random
,"-??
"in .? t.dt-4
noise,
is the
-nczeasin;
echoeS
It
as
The effectiveness or figure
10
4 ?
of merit of a FRI echo filter or ambiguity suppressor is
basically defined as
VTRI
VFRI
FAS =
"TRI
VFRI
out
in
Since at the input of the ambiguity filter the amplitude
of the FRI echoes from a given target is the same as the
amplitude of the TRI echoes, the formula for the ambiguity
suppression figure of merit reduces to:
As
out
In order for the increased PRF to have no objection-
able effects, it is necessary to reduce the amplitude of
the FRI echoes below the random noise level. Thus, the
ambiguity suppression figure of merit should be made
greater than the signal to random noise ratio at the out-
put of the filter.
In a research program of the type undertaken here,
it is of paramount importance to determine these figures
of merit both theoretically and experimentally as functions
of all radar parameters which have a significant influ-
ence on them. From this information the optimum perfor-
mance for a specified system can be determined and the
best system of any suggested group can be singled out.
Methods of Ambiguity Elimination
In order to eliminate ambiguities due to high pulse
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11
CIA-RDP81-01043R002900240002-8
Methods for Discriminating
False Range Indicating Echoes
Propagation
Information
Pulse
Distortion
(PDI)
Pulse
Attenuation
(PAI)
Modulation
Information
Modulation
of Pulse
Characteristics
Pu_se
Amplitude
(PAM)
Pulse
Width
(PWM)
Pu_se
Carrier
Frequency
Modulation
of Pulse
Spacing
Direction
Information
Direction of
Transmission and
Reception (ABDS)
Time
Sharing
Mixed
PRF
Methods for Discriminating False Range Indicating Echoes
Figure 1
Methods for Suppressing Discriminated
False Range Indicating Echoes
Optical-
Electronic
Filter
Storage-
Tube
Filter
Magnetic-
Storage
Filter
Pu_se
Interval
(PD1)
Comb
Filters
Methods for Suppressing Discriminated False Range Indicating Echoes
Figure 2
0
(D
0
CD
Ci)
Cl)
(D
CD
CD
(D
0
-o
-o
0_
0-,
0
: CIA-RDP81-01043R002900240002-8
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repetition rates the FRI echoes must first be discriminated
from the TRI echoes. The possible methods for accomplish-
ina this, which have been devised and investigated at the
Electronics Research Laboratory of Illinois Institute of
Technoloay, are shown in the block
AFf=r
the
diagram
of Figure 1
FRI echcs have been discriminated they
must he suppressed. Several possible methods which may
be applied are shown in the block diagram of Figure 2
These techniques not only suppress the FRI echoes but
also increase the signal-to-random noise ratio.
4 14
METHODS FOR DISCRIMINATING
FALSE RANGE INDICATING ECHOES
Introduction
In order to discriminate TRI echoes from FRI echoes
information is necessary to determine which transmitter
pulse caused the echo. This information may be provided
by the natural characteristics of pulse propagation or
by modulation of the transmitter output.
The natural means of discrimination are Pulse
Attenuation Information, Pulse Distortion Information,
and Antenna Beam Displacement Sorting. No extensive
investigation of these means of discrimination was done
since the first two are impractical and ABDS awaits the
development of a suitable rapid scan antenna.
Methods of modulating the transmitter output invest-
igated are Pulse Amplitude Modulation, Pulse Width Modu-
lation, Pulse Carrier Frequency Modulation, Pulse Code
Modulation, Pulse Interval Modulation, Time Sharing, and
Mixed Pulse Repetition Frequency. Of these methods PAM
and PWM are impractical because of the variations in
target characteristics; PCFM appears much less practical
than other methods because of complex equipment require-
ments., PCM breaks down when several targets are present;
and Time Sharing is limited in operation. Of the two re-
maining systems, PIM and Mixed PRF, both of which appear
practical, the PIM system was devisedfirst and consequent-
- _
ly has been investigated more completely. The Mixed PRF
system has been investigated theoretically and
appears to have merit.
15
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Pulse Attenuation Information
Under certain conditions the attenuations which a
_
pulse undergoes during propagation can be used to deter-
mine the approximate distance traveled by the pulse, and
hence provide a basis for resolving ambiguous range read-
ings. Since the energy in a pulse falls off with the
fourth power of the distance, there is considerable
rance information conveyed by the strength of the echo
relative to the transmitted pulse, Ambiguity elimination
based on this information would have worth-while possibili-
ties if the reflection coefficients of the targets and
the attenuation due to weather conditions were known.
SinC-e
the reflection coefficients of the targets and the
attenuation due to weatherconditions generally are un-
scaown, this ?ethod is considered to be impractical.1
?ulse Distortion information
puse "r=.*
,.L.g in a media becomes distorted as
t.rave;s, Cae cause of such distortion is due to the
"". ".?
aa7=e of the redia that is, the different
propagate with different
composinc
7:11.=" uise
'?????
c-= distortion is the hetero-
Cz
edia causes the pulse to split up m
_
tra-r-e' cv---r a of paths, each having slightly
crc-3C39 5'-15555 First Q.P.R.
_
pp
?
different length. When the pulse energy recombines at the
receiver the components are no longer in the same time
relationship. In the atmosphere the second effect (that
due to heterogeniety) appears to be predominant. Tests
carried out by 0. E. De Lange' using 3 millimicrosecond
pulses at 4000 megacles over a 22 mile path showed multi-
path transmission with path differences as great as seven
feet. This was sufficient to provide complete separation
of the received pulses. Distortion in the individual
pulse shapes Was undiscernable compared to that which
occurred due to combination of the pulses which had
traveled different paths.
A target having extension in the radial direction
from the radar antenna will broaden the received echo by
an amount approximately proportional to this extension.
Because of this fact and the fact that the geometry of
the target and the exact atmospheric conditions are not
likely to be readily available, the distortion due to
propagation does not provide a practical basis for ambig-
uity elimination.2
Antenna Beam Displacement Sorting
The directional information contained in the trans-
muted
-
mitted pulse can be utilized to provide a method for
10. E. De Lange, "Propagation Studies at Microwave
Frequencies by Means of Very Short Pulses", B.S.T.J.
31, 11-103 (January 1952).
2Signal Corps Contract DA36-039 SC-15555 First Q.P.R.
June 1952-September 1952, p 54.
17
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preventing the occurrence of false range indications.
During the interval between the sending of a transmitter
pulse and the reception of an echo due to that pulse the
radar antenna rotates through an angle proportional to
transit time of the pulse and hence to the range of
the target returning the echo. This information may be
utilized to prevent range ambiguities by employing
separate antenna beams, which rotate about the same axis,
for reception and transmission. The receiver antenna
beam lags behind the transmitter antenna beam by just the
amount required so that by the time the echo returns the
receiver antenna beam will have rotated into the position
occupied by the transmitter antenna beam when the pulse
was fired.
Absence of false range indications is achieved by
rotating the antenna beams with an angular velocity such
that completely different angular sectors are illuminated
by successive transmitter pulses, without having any un-
illuminated angular sectors.
The Principal disadvantages to this system are the
duplication of receiver equipment necessary in order to
observe
?????
8-11=1,
one sub-range simultaneously and the
special antenna scanner required)
Pulse Amplitude Modulation
In this method, range ambiguities are eliminated by
1Signal,Corps Contract DA36-039 SC-15555 First Q.P.R.
June 1952-September 1952, pp 55-58. second Q.P.R.
September 1952-December 1952, pp 52-62.
18
?
utilizing pulse amplitude information inserted in success-
ive pulses at the transmitter. Each transmitter pulse
amplitude is increased over that of the previous one by
the same amount until n pulses of different heights are
obtained, after which the modulation cycle is repeated.
The envelope of the transmitter pulse amplitude is a
saw-tooth wave. The amplitudes of successive echoes
from a given target have a similar saw-tooth envelope
which lags in phase behind that of the transmitter
envelope by an amount which is proportional to the
target range. Measurement of this phase lag gives
an approximate indication of the range and can hence be
used to eliminate false range readings.
This is accomplished by feeding the amplitude
modulated video output of the receiver through a variable
gain amplifier which has its gain controlled by a wave
form having the inverse variation to that of the trans-
mitter modulation wave form. The gain controlling wave
form is shifted in phase so as to match the phase delay
of the desired echo envelope. Then, in the output of
this amplifier, echoes from targets located at the
chosen range will have constant pulse amplitudes
whereas echoes from targets at other ranges will have
amplitude variations. The output of the variable gain
amplifier is passed through a blanking circuit which
removes the echoes with variable amplitudes and passes
the constant amplitude unambiguous signals. The blank
19
./
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ing pulse is generated by a circuit which compares each
echo with the echo from the same target due to the previous
transmitter pulse and whenever the amplitude difference
exceeds a specified amount, a blanking pulse is generated.
The extent of the range displayed unambiguously is influenc-
ed by the setting of the amplitude comparitor.
This method has two paramount disadvantages. One is
the fact that the transmitter peak power capabilities are
largely wasted by the amplitude modulation unless the per
cent modulation is small. Another is that the method
cannot integrate signals below the noise level because
information must be extracted for sorting before inte-
gration of the TRI echoes is possible.'
Pulse Width Modulation
In this method range ambiguities are eliminated by
utilizing pulse width information inserted in successive
pulses at the transmitter. The transmitter pulse width
is modulated so that n successive pulses have different
widths, after which the cycle is repeated. The radar's
major range is subdivided into as many sub-ranges as
there are different pulse widths in a modulation cycle,
and the information in each sub-range is separately
displayed: Extra apparatus would be required to
present all sub-ranges on one display.
The difference in width between an echo and the
-Siarco corps Contract DA36.-039 SC-15555 First Q.P.R.
June 195'--September 1952, pp 46-49.
20
transmitter pulse sent out just prior to reception of the
echo is utilized to sort the echo signal into the channel
which displays the sub-range in which the actual target
exists. A method of accomplishing this is as follows.
Each received echo triggers a pulse generator which
produces a pulse of the same width as the last trans-
mitter pulse generated. The width of this pulse is
compared with that of the echo just received and a voltage
proportional to the difference in widths is generated.
This voltage is applied to the switching circuit or tube
which connects the signal to the proper channel.
The principal drawback to this method is that it
cannot integrate received signals below the noise level
because information from individual pulses must be util-
ized in order to sort the echoes into the proper sub-ranges.
Another disadvantage is that the variation in pulse width
purposely inserted must be prohibitively large in order
to prevent variations in pulse width due to the radial
extension
tions .1
of the target from giving false range indica-
Pulse Carrier Frequency Modulation
With this system, successive pulses are transmitted
on different frequencies so that ambiguous pulses can be
separated on a frequency basis. Theoretically this method
is highly suitable for ambiguity elimination when MTI
"Signal Corps Contract DA38-039 SC-15555 First Q.P.R.
June 1952-September 1952, pp 34-38.
21
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operation is not required, but it appears to be inherently
incompatible with coherent MTI systems. The PCFM system
is very inefficient in its use of the radio spectrum
since it requires several times the bandwidth of a
conventional radar system.
It requires essentially a
complete separate receiver for each frequency unless the
application is such as to require the display of only
one sub-range at a time. The problem of automatic
frequency control is very severe with PCFM unless a
master oscillator power amplifier arrangement can be
used for the transmitter. This awaits the commercial
availability of suitable output tubes.'
Pulse Code Madulation
In this method, a group of pulses is transmitted
in place of each single pulse in an ordinary radar.
Successive pulse groups differ by the relative spacing
between the pulses or number of pulses in a group. After
n different pulse groups the modulation cycle is repeated.
The information conveyed by the coding of the echoes in
each group can be utilized to sort them into the appro-
priate channels.
The principal drawback to this method is that
overlapping of code groups resulting from closely spaced
targets will destroy the pulse group coding. Another
'Signal Corps Contract DA36-039 SC-15555 First Q.P.R.
June 1952-September 1952, pp 11-33. Second Q.P.R.
September 1952-December 1952, pp 17-27.
22
?
drawback is the difficulty of transmitting these high
power pulses in such quick succession. This method also
suffers from the inability to integrate signals below
the noise level.'
Time Sharing Radar
This system employs a radar having two different
repetition rates available. The operating time is
divided between these two repetition rates manually or
automatically.
Discrimination between TRI echoes and FRI echoes is
based on the fact that the range position of a FRI echo
on the display depends upon the time interval between
successive transmitter pulses. By switching the trans-
mitter repetition rate the FRI echoes are caused to
change range position on the display while the TRI
echoes remain fixed in range position. This allows.
the operator to discriminate between the TRI echoes
and the FRI echoes.
The discussion above applies most directly to an
A- scope presentation of a fixed azimuthal direction,
however, the system is usable even when a PPI display
is used. The main virtue of this system is its
simplicity and ease of incorporation into existing
radars, and thus is especially applicable to existing
radars having higher time around echoes. The disadvan-
'Signal Corps Contract DA36-039 SC-15555 Final Report
June 1952-August 1953, p 26.
23
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tage of this system is that even though the FRI echoes are
discriminated they are not easily suppressed. This re-
quires the operator to select the TRI echoes from the
display.1
Mixed PRF Radar
The Mixed PRF Radar is an extension of the Time Shar-
ing Radar. In this-system several different pulse repeti-
tion frequencies are used simultaneously instead of
sequentially as in the Time Sharing Radar.
The transmitter is triggered by a signal formed from
the sum of the outputs of n PRF generators of unequal PRF's.
The transmitter output pulses are therefore nonuniformly
spaced. The highest single PRF of the individual PRF
generators is chosen to be the highest unambiguous PRF
allowable for the radar. Thus the average overall PRF
can approach n times the unambiguous pulse repetition
rate and consequently ambiguous or many time around
echoes are present. Means for separating the TRI echoes
from the FRI echoes must be applied.
Since the echo spectrum of echoes from each PRF is
a different comb spectrum, separation of the FRI echoes
from the TRI echoes is possible by the use of comb
filters. The echo responses are applied to n sharply-
tuned comb filters in parallel, each of which will pass
only echoes from a particular PRF. Since each PRF is be-
'Signal Corps Contract DA36-039 SC-56696 First Q.P.R.
December 1953-March 1954 pp 13-17. Second Q.P.R. March
1954-June 1954 pp 16-20.
24
low the maximum unambiguous PRF, each channel, represent-
ing the output of one comb filter, presents the complete
radar range in one indicator sweep.
To obtain the full signal to noise integration im-
provement, the n channels must be combined into one dis-
play. Conceptually simplest is a system which features
a cathode ray tube with n electron guns all scanning
the same line on the face of the tube and each intensity
modulated by the output of one of the n channels. An-
other scheme involves n storage tubes. Each storage tube
stores the signal output from one channel and then a
simultaneous read (and erase) of all storage tubes would
add the stored information from all channels. This summed
signal would then be the signal for the final scope dis-
play.1
In the Mixed PRF system employing comb filters the
discrimination and elimination of the FRI echoes is
accomplished simultaneously in the comb filters. The
characteristics of comb filters for this application are
discussed in the section on ambiguity filters.
Pulse Interval Modulation
In this system, the transmitter operates like a
conventional radar except that the pulse repetition
1Signal Corps Contract DA36-039 SC-56696 Fifth Q.P.R.
February 1955-April 1955, pp 55-72. Sixth Q.P.R. May
1955-July 1955, pp 9-45.
25
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Declassified in Part - Sanitized Copy Approved for Release ? 50-Yr 2014/01/31 : CIA-RDP81-01043R002900240002-8
period is non-uniform. Since modulation of the pulse
repetition period can be accomplished in the triggering
circuits preceding the keyer, this type of modulation is
readily accomplished. In general, the amount of variation
required in the repetition period is small enough to
permit the ordinary resonant charging systems to be used
in the pulse generating network without difficulty.
When the echoes are received they are applied to
the vertical deflection or intensity mOdulation system
of an oscilloscope, the linear horizontal sweep of which
is triggered by each transmitted pulse of the radar. Let
Tj be the round trip echo time for a particular target.
If Tj is less than the duration of the sweep, the echo
will appear in the same position on every sweep since T
is constant. On the other hand, if T is somewhat longer
than the sweep duration, it will appear on the next sweep
(as an ambiguous echo) in a position corresponding to
where Ti 1 is the interval between the two
adjacent transmitted pulses. Since T. is constant but
Ti,i+1 is not constant, the position of the ambiguous
echo on the trace will vary from one sweep to the next.
Thus the FRI echoes appear spread out whereas the TRI
echoes all coincide. More distant targets can be viewed
as proper responses by introducing a fixed delay TD into
the sweep trigger system. Then the position of the echo
will correspond to Tj-TD which is fixed since TD is
constant. Of course, in this case, if Tj?
0 ^AAA ,
(,
--.4? 3 --,
u?) 441--? ?---v7Ani (I- S
c\I
'vv1v\e Ca
e. CO
a 0
I
-T-
1le
-
z 49.46.?AAA,-
uo 4_
V1
w
Cr)
kt,
cc:
II
a?.
V 00
c) 10-D
z z
---
0 (r) 0 't5r1
0 \13 It).4r-Am
-94
4-
k.0
8
c?i
kri
47
r?Lo
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Parl.e1 Vied
distribution to the output jacks)
Figure 8 shows the Panel, Rear, and Bottom views of
the PIM Modulator.
Counter
. This is a Model 5423R Berkeley Counter and acts as a
dividing Circuit. By pre-selecting a number n on the
keyboard of the Counter, there will appear one pulse at
the output of the Counter for every n pulses at the
input. The output pulse of the Counter is fed back to
the Modulator to re-cycle the modulation period.
?
Artificial Echo Unit
This unit is driven by the transmitter pulse from
the PIM Modulator and generates pulses of variable
width and amplitude, delayed from the input pulses by
an adjustable amount of time. Two pulses can be pro-
duced for each input pulse representing echoes from two
different targets.
Figure 9 is a block diagram of the Artificial Echo
Unit and Figure 10 is the schematic diagram. The in-
coming pulse from the PIM Modulator is amplified and
inverted in Vl. After being amplified and inverted
the pulse triggers a one-shot multivibrator (I/2)
which produces a pulse delayed from the input pulse by
1
Signal Corps contract No. DA-36039 SC-56696 Interim
Report December 1953-January 1955, pp 42-43.
49
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CJ1
01416.1411
w .4
0 co i_h
..-i _i, git.
0 I -, e o
o 0 1-1
:8 to.
o o
0 Ii
Z
ci-
hd
cf-
?
BUFFER
)2,4u7
+I06V
1st. DELAY
?
?
B U FFEf-
/2AU7 /a AU 7
4210V +I 06V +210Y +I06V
+2 by
A
PULSE GEN.
Au7
4-2101/
0 K
IMP UT .ek.5-
51<
[20km
200mm
J01(
/51(
10K
1_
.001
47K
\I /
1i I _ _ _
/ I
/ / ? I
3 47K VaB
V3A ,
V3.8
IN65 47K 2K
+76V +85V 491V
2-nd. DE LAY B UFFER PULSE GEN
12AU7 /2AU7 /2A(J7
4-2/eV
REPEAT OF CIRCUIT OF
/0K
41.5,K V2.11V2B,V 3A, V3B, Ofil)V9-13 .001
\
7\
VSA Hv52
221(
1
V7A 1,71 100
ithr
V
SN in -- 0.5
OUTPUT
SV LI. 0.5
NiII
3tcrsze-lit:te .:xbiguity Filter Operation,
ZiezetiTe-7mtems1ty-rod1lrtien, Baseline areek tatection
171;u:e 79
_
?
1200 VOLT ACCELERATION
n lc 10
INPUT
Sy >]
Nin
OUTPUT
V
SNin, 100
INPUT
V
S -0.5
Nin
OUTPUT
V
SNin = 0.5
Storage-Tube Ambiguity Filter Operation,
Negative-Intensity-iledulation, Bpseline Break Detection
Figure 80
203
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???
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The -r 11e-r-imeni-ai noise suppression figure-of-merit
at high acceleration voltage (2000 volts) appears to
le aPz=m-'17rily independent of n. This is because
the -rTaTinTrl noise generated internally by the storage-
?- Is aoprcmimately the same at both low and high
acceleration voltages, however, at high acceleration
the sression of the input random noise is
50 =eat thai- its contribution to the total noise at
the of the filter is negligible even for small
va2mes al. Since the total noise at the output of
th.e. filter at high acceleration voltage is substan-
only-the noise generated by the storage-tube
associated circuits, decreasing the signal-to-
noise ratio at the input does not appreciably decrease
s-54--to-noise ratio at the output and hence ?1.1
to increase as the input signal-to-noise ratio
decreases (see
definition of FN3 in the section en-
+ili--aed10-0201.41JTION). Higher beam acceleration
volteL,:es increase the ambiguity suppression figure-
L. do not have such a simply related effect
on noise session figure-of-merit.
7711' aCCUraey of the data presented in Figures 78
th.-Ila 76 is
si,oh as to these curves representative
of theTti,-747, of variation of the figures-of-
the output of the storage-tube
eteeifficmit and consequently the numeric-
al values :presented re.--)resent estimates of such
?
quantities as the ms value of the output noise and the
amplitude of the FRI echoes buried in random noise
several times their amplitude. These estimates were
consistently made so as to yield conservative values
for the figures-of-merit. At an n of 4, the possible
errors involved are of the order of 20 to 30 percent.
For values of n greater than 10 the possible errors
involved are of the order of 50 to 100 percent in the
direction such as to make the figures-of-merit pre-
sented in the curves too small.
The oscillograms of Figures 77 thru 80 may, in
some respects, give a clearer impression of the
operation of the Storage-Tube Ambiguity Filter with
the
can
for
two
The
two different types of modulation. Two comparisons
be made; first, between the two modulation systems
the same value of n in each, second, between the
values of n for each of the modulation systems0
first comparison shows that, at 1200 volts
acceleration, the ambiguity and noise suppression of
the negative-intensity-modulation system is better
than that of the deflection-modulation system at
large values of n. The second comparison shows that
the ambiguity and noise suppression increasesaas n
is increased,
Conclusions
Of all the Ambiguity Filters experimentally in-
vestigated, the Storage-Tube Ambiguity Filter with
205
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negative-intensity-modulation and baseline break datecton
appears to be the most versatile and practical, A simpli-
fied theoretical analysis indicates that an infinitely
large value of FAs is attainable under the assumption
that there is no random noise in the input and the
storage-tube has the idealized characteristics presented
in this report. Under very restrictive experimental
conditions, values of F up to approximately 50 have
AS
been attained (FRI echoes 34 db down from TRI echoes),
The noise suppression figure-of-merit of the filter
under the same conditions was between 5 and 15 (sianal-
to-noise ratio increased 14 db to 23 db, depending
upon the operating parameters).
A careful redesign of the negative-intensity-
modulation, baseline break detection Storage-Tube
Ambiguity Filter with particular emphasis on low
noise input and output circuits, high acceleration
voltaae, large external back plate to barrier grid
read-write potential shift, multiple read-out swee3s,
and a sharp cut off electron gun in the storage-tube
will result in a filter with higher figures-of-merit
than those obtained with the present equipment.
206
MAGNETIC-STORAGE AMBIGUITY FILTER
Introduction
The performance of PIM and Mixed PRF systems in elim-
inating range ambiguities due to high pulse repetition
rates is enhanced bY ambiguity filters which suppress the
false range indicating (PRI) echoes after they have been
discriminated from the true range indicating (TRI) echoes,
and which increase the signal-to-noise ratio.
In the Mixed PRF system the discrimination and
suppression are performed simultaneously in comb filters
It has been pointed out that effective comb filters can
be synthesized from linear amplifiers, constant time
delay devices, and linear adders.1 A magnetic-storage
device could form the constant time delay mechanism in
such a comb filter. In this capacity, the magnetic-
storage device would operate with a linear input-output
amplitude relationship. Thus, the device would operate
in the manner of conventional magnetic recording
devices. Such operation has been extensively described
in the literature.
In the PIM system, the magnetic-storage device could
be operated either linearly, or non-linearly, that is,
the magnetic-storage media and/or the associated circuitry
could be operated either within their linear range or
outside theix.linear range.
1Signal Corps Contract No. DAf',,36-039 50-56696, Fifth
Q.P.R. February 1955-April 1955, pp 119-170.
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Maga,. etic-Storage Iri'niguity _Filter
A magnetic-storags. ambiguity filter system (Series-
Read System) is shown in Figure 81. The principle of
operation can be most easily understood by considering
linear
operation of
Information is
storage media which
heads at a
speed T.
all the system elements0
recorded on two tracks on the magnetic
moves under the writing and reading
One track (trigger-track) is used to
provide the timing of-the.interv.al modulated trigger
pulses for the transmitter. The video output of the
receiver is recorded on the second track (echo-track).
Each track has
one write-head and n read-heads spaced
at non-equal intervals, where n is the number of intervals
in the ?IM modulation cycle. The magnetic write-head and
read-heads along the echo-track have reversed spacing
compered to the trigger-track head spacing, as shown in
Figure 81.
The triggering of the transmitter is accomplished
as follows. A trigger-Pulse is recorded on the trigger-
track by the write-head. After a time interval T
(1)
Tn X,
0,1
0,1 V
0,1
the pulse reaches the first read-head and the signal is
a-p1;-7-ied and used to trigger the transmitter. After an
additioral time intervalT12 has elapsed,
,
?
(2) T = x2
1,2
the pulse reaches the second read-head and the signal is amplified
208
4?
?to
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and used to trigger the transmitter again. This is re-
peated until the pulse reaches the last read-head on the
trigger-track. The signal here is not only used to trigger
the transmitter but also to trigger the indicator sweep and
record a new trigger-pulse on the trigger-track. The en-
tire modulation cycle is repeated as the new trigger-pulse
travels along the read-heads.
During the entire modulation cycle the video output
of the receiver is continuously recorded on the echo-track.
After one complete modulation cycle the echoes are record-
ed on the echo-track of the magnetic-storage media between
the write-head and the last read-head. The read-head
spacing causes TRI echoes to appear under all the read-
heads simultaneously as the magnetic-storage media moves
past the heads. FRI echoes do not appear under all read-
heads simultaneously and hence no integration of FRI
echoes occurs. The integrated TRI echoes and the non-
integrated FRI echoes are displayed on the indicator.
The indicator sweep duration is
(3) T X24- 7'11)
so that the entire range is presented0
presentation of the entire radar range
integrated to a highe-r-degree than the
random noise.
As an example, consider a system with n equal to
three, and three targets located so that their echoes
are first, second, and third time-around echoes. Figure
The result is a
with TRI echoes
FRI echoes and
210
?
82A shows the head spacing along the two tracks. Figure
82B shows the equivalent range positions of the three
targets. Figure 820 shows the echoes due to the three
targets (a, b and c) and the transmitter pulses (T) record-
ed on the echo-track after several modulation cycles have
elapsed, along with the positions of the echo-track read-
heads at the start of the indicator sweep. Figure 82D
shows the conditions after the magnetic-storage media has
moved a distance xa? The recorded echoes due to the first
target are all under read-heads, and the output of the
three read-heads is added to give the echo at xa on the
indicator. A similar addition of outputs occurs as the
second and third echoes appear simultaneously under the
three read-heads after the magnetic-storage media has
moved distances of xb and xcl respectively. The FRI
echoes recorded on the echo-track appear as small responses
between the TRI echoes on the indicator display, as shown
in Figure 82E.
The common moving magnetic-storage media for gener-
ating the PIM modulation pulses and storing the echo
information prior to integration alleviates the necessity
for extreme long-time (more than 10 modulation cycles)
stability and accuracy in the speed of the magnetic
storage media? Short-time (less than 10 modulation
cycles) stability must be sufficiently good so as not to
degrade the integration of TRI echoes.
Ten modulation
cycles, or less, is chosen as the basic short-time
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211
,
?
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v v
A2 ?"I--
t--X.),---411--Y2
/1r-
A. Head Spacing Along Tracks
HAAR
b c
)4 c
B. Equivalent Target Ranges
Tab e Ta bc
Xc
X6
4.?Xa-
iii
7 al. c Ta b
I DOI II 1:0111111311
C. Conditions at Start of Indicator Sweep
fTII
titt
X c
A4*---7Z1=1:
T abc T
I
ml III
D. Conditions After Movement of Distance X1
Tpa,
IriMiii iirtrir
X C
E. A - Scope Display After Movement of Distance X1 + X2 + X3
RANGE-
Operation of Series - Read Magnetic - Storage Ambiguity Filter System
Figure 82
212
?
I
interval because under most practical search conditions
a target is illuminated by the antenna beam for approx-
imately ten, or less, modulation cycles.1 Short-time
stability is provided primarily by the momentum of the
mechanical parts in the system.
Another magnetic-storage ambiguity filter system
(Series-Write System) is shown in Figure 83. The operation
of this system is similar to the operation of the Series
Read System. Transmitter triggering is accomplished in
exactly the same manner in both systems. The Series-
Write System uses n write-heads on n separate echo-tracks
to record the echo information from the receiver. The
distance between adjacent heads along the tracks is non-
uniform, but the spacing is the same along each of the
tracks. This eliminates the problem of obtaining reverse
head-spacing accuracy which occurs in the Series-Read
System. The positioning of the write-heads and read-
heads along the echo-trabks causes TRI echoes to appear
simultaneously under the read-heads as the magnetic
storage media moves. FRI echoes do not appear under the
read-heads simultaneously and consequently are not inte-
grated. The indicator sweep displays the entire radar
range with TRI echoes integrated to a higher degree than
FRI echoes and random noise, similarly to the Series-Read
3ystem.
'Signal Corps Contract No. DA-36-039 SC-56696 Seventh Q.
P.R., August 1955-October 1955, pp 98-148.
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43
fa.
0
0
4
4
214
'CS ?
04
0
Series-Write Mhgnetic-Storage Ambiguity Filter System
A third magnetic-storage ambiguity filter system,
which is a variation of the Series-Write System, involves
integration of the echo information in the magnetic-
. , storage media. The system is the same as the Series-
Write System shown in Figure 83, except that the n write-
heads are arranged in-line on one echo-track and only one
read-head and read amplifier are used. This eliminates
n-1 read-heads and read amplifiers and the adder in
addition to requiring only one echo-track on the magnetic-
storage media. This system is most applicable for use
of the non-linearity (magnetic saturation) of the magnetic
storage media to increase the ambiguity suppression and
signal-to-noise ratio improvement.
Magnetic-Storage Media Speed
The minimum allowable speed of the magnetic-storage
media is dependent upon the highest frequency to be
recorded and read out, the effective air-gap widths of
the recording and reading heads, and the granularity
of the magnetic-storage media.
The average particle size of currently used magnetic-
storage coatings is approximately 0.015 mil, and particles
rarely exceed 0.025 mil in size. This theoretically limits
the shortest wavelength that can be recorded to approximate-
ly 0.05 mil. Recorded wavelengths as short as one mil
have been achieved practically, with signal-to-noise ratios
215
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as high as 60 db.1
The finite size air-gaps of the heads have an averag-
ing effect on the signal during both recording and read-
ing. The write-head air-gap in addition to averaging the
signal causes a complex distortion due to the magnetic
hystersis of the magnetic-storage media. An approximate
relation between the minimum speed necessary to record
and read out a given requency.signal with a specified
accuracy and size of air-gaps in the heads can be ob-
tained by assuming that the only effect of the gaps is
to average the signal. The averaging interval is taken
as the length of time it takes a point on the magnetic-
storage media to travel a distance equal to the air-gap
width. Since two air-gaps are involved, the signal is
averaged twice. The averaging time interval during
recording Tw is
(4) Tw xw
where
xw = write-head air-gap width
v = speed of magnetic-storage media
and the averaging time interval during reading Tr is
(5) T xr
where
xr = read-head air-gap width
?
15. J. Begun, "A Survey of Magnetic Recording", Electrical
Engineering, December 1954, pp 1115-1118. -
216
The output signal will be proportional to the double
average of the input signal. For a sinusoidal input signal
t+Tt+Tw
lr
V
out = ?f A sin 2nft dt dt
Tr t Tw t
where
V
= output signal out
A = amplitude of input signal
f = frequency of input signal
K = constant of proportionality
Evaluating the integrals gives
KA
(7) V -
out T'T 4nf2
W
sin 2nf(t+T ) - sin 2nft
- sin 211f(It+Tr +Tw ) + sin 27tf(t+Tu-di
-
Equation (7) can be reduced to
T
KA sin nfTr sin nfT T+
sin 2 " ?,
)
(8) Vout -
TT n2f2
2nf(t+ ,
r w
For T