HF SPACED LOOP ANTENNA

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP76-00451R000200010013-1
• Release Decision: RIFPUB
• Original Classification: K
• Document Page Count: 130
• Document Creation Date: December 9, 2016
• Document Release Date: August 28, 2001
• Sequence Number: 13
• Publication Date: July 1, 1967
• Content Type: REPORT

Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
AD
TECHNICAL REPORT ECOM- 01960-F
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
? o ? ?
??
?
HF SPACED
LOOP ANTENNA
FINAL REPORT
BY
J.D.MOORE ? M.P.CASTLES
JULY 1967
DISTRIBUTION STATEMENT
Each transmittal of this document outside the Depart-
ment of Defense must have prior approval of CG,U.S.
Army Electronics Command, Fort Monmouth,N.J.
Attn: AMSEL-WL-C
? ? ? ? ? ? ? ? ?
ECOM
UNITED STATES ARMY ELECTRONICS COMMAND. FORT MONMOUTH, N.J.
CONTRACT DA28-043-AMC-01960(E)
SOUTHWEST RESEARCH INSTITUTE (16-1855)
Son Antonio ,Texos
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
NOTICES
Disclaimers
The findings in this report are not to be construed as an official
Department of the Army position unless so designated by other authorized
documents?
The citation of trade names and names of manufacturers in this
report is not to be construed as official Government indorsement or
approval of commercial products or services referenced herein.
Disposition
Destroy this report when it is no longer needed. Do not return it
to the originator.
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
Approved For Release
001/19/03 : CIA-RDP76-00451R000200010013-1
TECHNICAL REPORT ECOM-01960- F
HF SPACED LOOP ANTENNA
FINAL REPORT
JULY 1967
1 FEBRUARY 1966 TO 31 JANUARY 1967
Report No.4
CONTRACT NO. DA 28-043AMC-01960(E)
DA TASK NO. 566 79191 D908 07 12
SwRI PROJECT 16-1855
DISTRIBUTION STATEMENT
Each transmittal of this document outside the Department or
Defense must hay, prior approval of CO,U.S. ARMY ELEC-
TRONICS COMMAND, Fort Monmouth,N.J.
Attn. AMSEL-WL-C
Prepared By
J.D. MOORE AND M.P.CASTLES
SOUTHWEST RESEARCH INSTITUTE
SAN ANTONIO , TE XAS
For
U. S. ARMY ELECTRONICS COMMAND, FORT MONMOUTH, N. J .
ApprAve,cI#3
UGLAS N. TRAVERS,Director
Applied Elect romognetics
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
1. ABSTRACT
Coaxial spaced loop antenna theory is reviewed with emphasis on
patterns as a function of signal polarization and angle of elevation. Experi-
mental work with three broadband antennas has verified that the desired
theoretical performance can be obtained in a practical design.
The major effort of this project was an advanced development/
feasibility model of an HF spaced loop delivered as a component of a 4 to
8-MHz direction finder system. The rotation pedestal and visual indicator
of existing DF systems were used with minor modifications. The evalua-
tion of the HF spaced loop DF set verified that the CW sensitivity design
goal of 10 ?v/m was met over the operating range. The desired DF
accuracy requirement for skywave signals was achieved for elevation
angles of arrival up to 85?, and 561 azimuth bearings on stations at dis-
tances greater than 300 miles between 4 and 8 MHz produced a standard
deviation of Z. 67?.
Possible design improvements are listed based upon the design,
construction, and evaluation experience of the first model. A major
engineering improvement in the aural null control method would be
valuable, in which case the spaced loop can be used more effectively
in a manual left-right or automatic left-right DF mode. High speed
sampling using this capability is suggested as a method of reducing
response time on keyed signals. An alternative solution would be faster
antenna rotation.
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
2. TABLE OF CONTENTS
1. ABSTRACT
2. TABLE OF CONTENTS
Pae
1
2
3. LISTS 4
3. 1 List of Illustrations 4
3. 2 List of Tables 9
4. FACTUAL DATA 10
4. 1 Phase I - Study and Experimental Investigation 10
4. 1. 1 Introduction 10
4. 1. 2 Review of Spaced Loop Theory 11
4, 1. 3 Sense for the Coaxial Spaced Loop Antenna 16
4. 1. 4 Theoretical Coaxial Spaced Loop DF and Sense
Patterns 17
4. 1. 5 Experimental Investigation 20
4. 2 Phase II - Design Phase 32
4. 3 Phase III - Equipment Construction and Evaluation 33
4. 3, 1 Introduction 33
4. 3. 2 Description of the HF Spaced Loop Direction
Finder Set 33
4. 3. 2. 1 System Description 33
4. 3. 2. 2 Advanced Development/Feasibility HF Spaced
Loop Antenna 37
4. 3. 2. 3 Rotation Pedestal 52
4. 3. 2. 4 Antenna and Pedestal Control Unit 55
4. 3.2. 5 Requirements for Equipments Not Furnished
to the Contractor 57
4?3. 2. 5. 1 DF Indicator 57
4. 3. 2. 5. 2 The Receiver 65
4. 3. 3 Evaluation of the Equipment 67
4. 3. 3. 1 Field Site and Equipment 67
4. 3. 3.2 Sensitivity 70
4. 3. 3. 3 Performance for a Local Target 72
4. 3. 3. 4 Performance Using an Aircraft-Mounted
Target Transmitter 76
4. 3. 3. 5 Performance on Skywave Signals 77
4. 3. 3. 5. 1 Description of the Tests and Procedures 77
4. 3. 3. 5. 2 Test Results 86
Approved For Release 2001/09/03 CIA-RDP76-00451R000200010013-1
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
2. TABLE OF CONTENTS (Con.t'd)
4. 3. 3. 6 Power and Torque Requirements in
Relation to Rotation Speed
4. 3. 4 Maintenance
4.3. 5 Recommendations for an Improved Design
5. LIST OF REFERENCES
6. DISTRIBUTION LIST
3
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
Page
110
112
117
121
124
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
3. LISTS
3.1 List of Illustrations
Figure Page
1 Common Spaced Loop Antennas 12
3
4
5
6
7
8
9
Normalized Elevation Patterns for the Coaxial
Spaced Loop, the Vertical Coplanar Spaced
Loop, and the Simple Loop Antennas
Coaxial Spaced Loop and Simple Loop Patterns
as a Function of Signal Polarization and Angle
of Incidence
Coaxial Spaced Loop and Sense Patterns as a
Function of Signal Polarization at 0 = 78?
(12? Above the Horizontal)
Coaxial Spaced Loop and Sense Patterns as a
Function of Signal Polarization at 0 = 60?
(30? Above the Horizontal)
Coaxial Spaced Loop and Sense Patterns as a
Function of Signal Polarization at 0 = 45?
(450 Above the Horizontal)
Coaxial Spaced Loop and Sense Patterns as a
Function of Signal Polarization at 0 = 25?
(65? Above the Horizontal)
Coaxial Spaced Loop and Sense Patterns as a
Function of Signal Polarization at 0 = 15?
(75? Above the Horizontal)
Coaxial Spaced Loop and Sense Patterns as a
Function of Signal Polarization at 0 = 5?
(85? Above the Horizontal)
15
19
21
22
23
24
25
26
10 Breadboard HF Coaxial Spaced Loop Antenna
(Model 1) 28
4
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
3.1 List of Illustrations Cont(d)
Figure Page
11 Breadboard HF Coaxial Spaced Loop Antenna
(Model 2) Mounted on the AN/PRD-7 and 8
Pedestal 29
12 Breadboard HF Coaxial Spaced Loop Antenna
(Model 3) 30
13 Breadboard HF Coaxial Spaced Loop Antenna
(Model 3) Mounted on the AN/PRD-7 and 8
Pedestal 31
14 Components of Portable HF Spaced Loop Direc-
tion Finder Set Constructed by Southwest
Research Institute and Shown in Transit Bags 35
15 Interconnection and Mast Extension Schematic 38
16 The Disassembled Portable HF Spaced Loop
Antenna in the Transit Case 39
17 The Disassembled Portable HF Spaced Loop
Antenna
18 Assembled Portable HF Spaced Loop Antenna
19 Portable HF Spaced Loop Antenna on the
Modified AN/PRD-7 and 8 Pedestal
20 Portable HF Spaced Loop Antenna Schematic
21 Field Effect Transistor Source Follower
Schematic
22 Broadband Preamplifier Schematic
23 Recommended Voltage Regulator Schematic
for SwRI Spaced Loop Antennas
40
41
43
44
45
46
47
24 Electronics Housing with Side Door Removed
for Access to Electronics Chassis 49
5
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
3.1 List of Illustrations jont'd
Figure Page
25 Electronics Chassis 50
26 Top Access Door Removed for Access to Cross-
over Switching Assembly 51
27 Pedestal and Control Cable Removed from
Carrying Bag 53
28 Pedestal Wiring Schematic 54
29 Control Unit in Carrying Bag 56
30 Control Unit Schematic 58
31 Control Unit Front Panel 59
32 DF Indicator Schematics with Modifications 64
33 DF IF Amplifier and Video Detector Schematic
(Tube Type) 66
34 DF IF Amplifier and Video Detector (Transistor) 68
35 Equipment Used in Evaluation of HF Spaced
Loop 69
36 Spaced Loop, Simple Loop, and Sense Patterns
for Advanced Development! Feasibility Model
HF Spaced Loop Antenna as a Function of
Signal Polarization 0 = 82? (8? Above the
Horizontal)
37 Spaced Loop, Simple Loop, and Sense Patterns
for Advanced Development/Feasibility Model
HF Spaced Loop Antenna as a Function of
Signal Polarization 0 = 82? (8? Above the
Horizontal)
6
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
73
74
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
3.1 List of Illustrations (Cont'd)
Figure
38 Spaced Loop, Simple Loop, and Sense Patterns
for Advanced Development! Feasibility Model
HF Spaced Loop Antenna as a Function of
Signal Polarization 0 = 82? (8? Above the
Horizontal)
Page
75
39 Sample Skywave Bearing Data Sheet (Continuous
Rotation) 80
40 Sample Skywave Bearing Data Sheet (Aural Null) 81
41 Typical Skywave Patterns -Amplitude
Modulation (A3) 82
42a Typical Skywave Patterns Frequency Shift CW (F1) 84
42b Typical Skywave Patterns Unm.odulated Carrier (A0) 84
43 Typical Skywave Patterns-CW (A1)-AT 30 rpm 85
44 Typical Skywave Patterns-CW (A1)-5 to 10 rpm 87
45 Histogram of Breadboard Antenna Skywave
Bearing Data - Total Sample 88
46 Histogram of Breadboard Antenna Skywave
Bearing Data - Continuous 30 rpm Mode 89
47 Histogram of Breadboard Antenna Skywave
Bearing Data - Aural Null Mode 91
48 Histogram of Breadboard Antenna Skywave
Bearing Data - Stations Less Than 300 Miles 92
49 Histogram of Final Antenna Skywave Bearing
Data - All Data Greater Than 300 Miles 95
50 Histogram of Final Antenna Skywave Bearing
Data - Aural Null Greater Than 300 Miles 96
7
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
3.1 List of Illustrations (Cont'd)
Figure
51 Histogram of Final Antenna Skywave Bearing
Data - Continuous Rotation Greater Than
300 Miles - Class A or Symmetrical Pattern
Every Sweep
52 Histogram of final Antenna Skywave Bearing
Data Continuous Rotation Greater Than
300 Miles - Class B or Symmetrical Pattern
Every 2 to 3 Sweeps
53 Histogram of Final Antenna Skywave Bearing
Data - Continuous Rotation Greater Than
300 Miles - Class C or Symmetrical Pattern
Every 4 to 6 Sweeps
54 Histogram of Final Antenna Skywave Bearing
Data - Continuous Rotation Greater Than
300 Miles - Class D or Symmetrical Pattern
Every 7 to 9 Sweeps
55 Histogram of Final Antenna Skywave Bearing
Data - Continuous Rotation Greater Than
300 Miles - Class E or Symmetrical Pattern
After More Than 9 Sweeps
Page
97
98
99
100
101
56 Histogram of Final Antenna Skywave Bearing
Data - Continuous Rotation Greater Than
300 Miles - Class F or Symmetrical Pattern
Never Occurred 102
57 Histogram of Final Antenna Skywave Bearing
Data - All 30 Mile Data 10.7
58 Histogram of Final Antenna Skywave Bearing
Data - All 100 Mile Data 108
59 Histogram of Final Antenna Skywave Bearing
Data - 200 Mile KLC at Galveston, Texas 109
60 Sense Network 118
8
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
3.2 List of Tables
Table
List of Components for Portable HF Spaced Loop
Direction Finder Set
2 Transit Bag Nomenclature, Contents, and Weights
for the HF Spaced Loop DF Set
3 Description of Control Unit Functions
4 Summary of Final Sensitivity Data on the Final
Advanced Development/Feasibility Model of the
HF Spaced Loop Antenna at 4-kHz Receiver Band-
width
5
6
List of Stations Used in the Breadboard Antenna
Skywave Bearing Tests
Page
34
36
60
71
93
Summary of Data as a Function of Signal Class
on the Final Antenna 103
7 List of Stations Used in the Final Antenna Sky-
wave Bearing Tests
8
9
Operator Standard Deviation and Mean Error
Current Drain and Predicted Battery Life
Using 70-rpm AN/TRQ-23 Pedestal Motor
105
111
113
10 Current Drain and Predicted Battery Life Using
30-rpm AN/PRD-7 & 8 Pedestal Drive Motor 114
Approved For Release 2001/09/039: CIA-RDP76-00451R000200010013-1
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
4, FACTUAL DATA
4.1 Phase I - Study and Experimental Investigation
4. 1. 1 introduction
The spaced loop antenna has been the subject of frequent but unsus-
tained development. Several workers have stated that the antenna offered
distinct advantages for both general and specific applications in the HF
frequency range. The work of Caplin and Bagley(1)'?'inWorldWar Il pro-
duced a mobile spaced loop direction finder with reasonable sensitivity
and reported excellent skywave performance. The system was used
strictly in an aural null mode. At that time, the system development was
apparently dropped because Adcock systems with high speed goniometer
and cathode ray tube indicators were much easier to use than the aural
null spaced loop system developed by Caplin and Bagley.
More recently, Bailey(') refers to the spaced loop antenna as a
rotating interferometer. He states that the rotatittig spaced loop antenna
can be an effective high angle direction finder provided a major technolo-
gical breakthrough can be achieved with the spaced loop. Primary prob-
lems were, as he saw them, sensitivity and response time.
The work of this program under the guidance of Technical Guide-
lines for DD&F No. 810000 titled "HF Spaced Loop Antenna, " dated
25 October 1965, has concentrated on the development of a spaced loop
antenna for portable use in the frequency range of 4 to 8 MHz. The final
advanced development/feasibility model delivered is used with a modified
portable antenna pedestal of the AN/PRD-7 and 8 type.
It is felt that the advanced development/feasibility HF coaxial
spaced loop antenna developed under this program presents a significant
advance in the state-of-the-art in spaced loop engineering. It is, how-
ever, recognized that significant improvements may be made in the
present development. A later section of this report outlines these pos-
sible improvements.
The experimental work of this program along with details of the
design phase were discussed at length in the three quarterly reports. (3, 4, 5)
The emphasis of this report will be placed on the construction and evalua-
tion of the final development/feasibility model. However, a review of the
)1sSuperscript numbers refer to List of References at end of this report.
Approved For Release 2001/09/0j3?: CIA-RDP76-00451R000200010013-1
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
theoretical data given in Quarterly Report No. 1(3) indicates that the
theoretical portion should be repeated here with revisions for clarifica-
tion of certain points.
4. 1. 2 Review of Spaced Loop Theory
There are three common spaced loop types. They are: the coaxial,
the vertical coplanar, and the horizontal coplanar spaced loop antennas.
The three types are illustrated in Figure 1 where the antennas are shown
with a parallel opposition connection. The loops of the spaced loops of
Figure I could be connected in a series opposition connection to obtain
the spaced loop mode; however, the parallel opposition connection shown
will generally yield the highest first parallel resonant frequency. The
loops could also be connected in a parallel aiding or series aiding con-
nection to obtain a simple loop mode. (7)
Far field radiation terms for the three common spaced loop anten-
nas are available from the published field equations for the general spaced
loop antenna. (8, 9) The near field terms will not be considered because,
with the exception of local site effects and reradiation, this development
has only considered far field signals. These equations are:
Spaced Polarization
Loop_ Vertical Horizontal
Coaxial
E - -1133V6* [ 1 ] sin 0 sin 24)
O 2, Or
(1)
ip3vwp. [ I
-
sin 20 sin2 4) (2)
3-3T
Vertical3\rum: F 1 sin 0 sin2 4) (3) I(33Vcop. 1
Eo -
Coplanar L - 41T jf3r]
Horizontal
Coplanar
where
E0 = 0
(5)
E _ -I03Vtop. { 1
2ir jf3r
sin 20 sin 24) (4)
sin2 0 sin 4) (6)
V = volume of spaced loop antenna (loop area multiplied by
number of turns in each loop times loop spacing)
(I) = azimuth
0 = angle of incidence
I = average loop current
Approved For Release 2001/09/P1 : CIA-RDP76-00451R000200010013-1
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
a. COAXIAL SPACED LOOP
PARALLEL OPPOSITION
b. VERTICAL COPLANAR SPACED
LOOP PARALLEL OPPOSITION
c. HORIZONTAL COPLANAR SPACED LOOP
PARALLEL OPPOSITION CONNECTION
FIGURE 1 COMMON SPACED LOOP ANTENNAS
Approved For Release 2001/09/n: CIA-RDP76-00451R000200010013-1
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
= ZTr/N. where is the wavelength
= 2-rr times frequency
= permeability of medium
radial distance from the center of the antenna
From the far field radiation term equations for the horizontal
coplanar spaced loops [Equations (5) and (6)1, it was obvious that this
antenna could be eliminated for further consideration because it has no
response for vertical polarization.
The equivalent equations for a simple loop antenna orientated so
the plane of the loop is parallel to the loops of the coaxial spaced loop
of Figure 1 are.
Polarization
Vertical
j132.Ao.T. I- 1
E0 - I
2-rr ji3r
cos cl)
-
Horizontal E _ 1
cos sin cl)
[
2,Tr jpr_
where A = effective area of the loop (number of turns times loop area).
The equations for the coaxial spaced loop, the vertical coplanar
spaced loop, and the simple loop indicate that both the elevation response
and azimuth response of the antenna are independent of frequency. The
terms in front of the trigonometric functions determine the amplitude and
phase of the antenna output voltage. The equations for the coaxial spaced
loop, vertical coplanar spaced loop, and simple loop may be simplified if
each equation is divided by a normalizing term but retaining phase. If
the following normalizing terms are used.
Coaxial Spaced Loop and Vertical Coplanar Spaced Loop
I133Vcop,
N =
47r
ji3r
Simple Loop
cop,
1
N = lpA
2 Tr
Approved For Release 2001/09/0133: CIA-RDP76-00451R000200010013-1
( 9 )
(10)
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
The resulting normalized far field radiation terms with phase retained for
vertical and horizontal polarization for the three antennas are:
Antenna
Polarization
Vertical
Horizontal
Coaxial
Vo = -2 sin 0 sin 24)
(11)
V = 2 sin 20 sin2c1)
(12)
Spaced Loop
Vertical
Coplanar
Vo = 4 sin 0 sin243
(13)
V sin 20 sin 243
(14)
Spaced Loop
Simple
Vo = j cos 43
(15)
Vd) = j cos 0 sin 43
(16)
Loop
From the normalized equations, it can be seen that the elevation
patterns for the coaxial and vertical coplanar spaced loops are identical.
The normalized elevation patterns for these two spaced loops and the
simple loop antenna are given in Figure 2. (These elevation patterns
exist in free space at all azimuth angles except at the nulls, as indicated
in Figure 2. ) The spaced loops have a maximum along the horizontal and
a minimum overhead for vertical polarization, while they have the maxi-
mum at 450 above the horizontal for horizontal polarization. On the basis
of the elevation patterns alone, there was no significant difference (for the
requirements of this program) between the coaxial spaced loop and the
vertical coplanar spaced loop.
For the 4 to 8-MHz frequency range, only groundwave signals will
be continuously vertically polarized. The skywave polarization will vary
from pure vertical polarization and to pure horizontal polarization with
these two conditions probably occurring only a small percentage of the time.,
It is felt by workers at Southwest Research Institute that the four null
, sin 24) pattern is easier to interpret than the two null sink!) pattern. There-
fore, it appeared that the coaxial spaced loop would be the more desirable '
for this requirement where both groundwave and skywave signals are
anticipated. It also had the advantage of being a better known design, and,
perhaps, less critical to build for vertical polarization.
Analytical work performed for the Bureau of Ships(8) and summarized
in the literature(9)indicated another factor. The patterns for the vertical
coplanar spaced loop antenna change significantly as the antenna moves
into the near field of a signal, whereas the coaxial spaced loop patternia,
the same for both near field and far field signals. The vertical coplanar
Approved For Release 2001/09/0Y: CIA-RDP76-00451R000200010013-1
Approved For Release 2001/09/03 : C1A-RDP76-00451R000200010013-1
VERTICAL POLARIZATION
(4) * 0?,90?,180?, OR 2700)
HORIZONTAL POLARIZATION
(4)*0? OR 1800)
COAXIAL SPACED LOOP
VERTICAL COPLANAR SPACED LOOP
VERTICAL POLARIZATION
(4)* 90?. OR 2700)
SIMPLE LOOP
FIGURE 2.
HORIZONTAL POLARIZATION
(0* 0? OR 180?)
NORMALIZED ELEVATION PATTERNS FOR THE COAXIAL SPACED LOOP,
THE VERTICAL COPLANAR SPACED LOOP,
AND THE SIMPLE LOOP ANTENNAS,
Approved For Release 2001/09/0?: C1A-RDP76-00451R000200010013-1
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
would be more affected by local site conditions and the presence of a sup-
port mast. For these reasons, it is felt that the coaxial spaced loops
should be used for the current requirement.
The same analysis has produced an excellent method of predeter-
mining spaced loop signal plus noise to noise sensitivity in terms of antenna
parameters. The specific application of this technique to this develop-
ment is discussed in Quarterly Report No. 1. (3)
4.1.3 Sense for the Coaxial Spaced Loop Antenna
The choice of the coaxial spaced loop for the portable and mobile
land-based requirement of this program led to a need to extend the
previous work performed in the 20 to 150-MHz frequency range in order
to meet an increase in angle of elevation requirement from 450 to
85.. (7, 10-18) The sense method used for the 20 to 150-MHz antenna was
also reviewed in terms of the increased angle of elevation requirement.
When both the coaxial spaced loop and simple loop are used indi-
yidually, there remains a two-way ambiguity for all signal polarizations.
*1___
This two-way ambiguity can be resolved by summing the coaxial spaced
loop with a simple loop of the proper amplitude and phase (the loop must be
parallel to the loops of the coaxial spaced loop). If the simple loop output
is shifted by 90? and an amplitude control factor A is applied from the
normalized far field radiation terms [Equations (11), (12), (15), and (16)),
the sense function can be described by the following expression:
Vertical Horizontal
Esense.-- -2 sin 0 sin 24 + 2 sin 20 sin2(1) +
l J
-.
Coa--Y xial Spaced Loop
Vertical
A (cos cl)
Horizontal
cos 0 sin ()
Simple Loop
(17)
The resulting sense pattern shifts the correct spaced loop null in a
_ _
_ _ _
clockwi_ae_dir_e_c_tion. (The reciprocal null, which is 180? from the correct
bearing, is shifted counterclockwise. ) If the simple loop signal is shifted
in phase by 270?, then the correct spaced loop null is shifted counterclock-
wise.
Approved For Release 2001/09/of: CIA-RDP76-00451R000200010013-1
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
4. 1.4 Theoretical Coaxial Spaced Loop DF and Sense Patterns
A computer program has evolved from work on a VHF spaced loop
antenna under Contract DA 28-043 AMC-01633(E) which permitted the rapid
computation of the theoretical antenna patterns as a function of signal
polarization and angle of elevation. The computer program for the cal-
cuLation of coaxial spaced loop patterns, simple loop patterns, and sense
patterns as used to calculate the theoretical patterns given in Quarterly
Report No. 1(3)was correct. However, the equation describing the pro-
gram contained errors. The program based on the normalized far field
terms of Equations (11), (12), (15), and (16) with the appropriate cor-
rections is
where
VT = EvejPv [ -2 sin 0 sin 2c1) Ecxecx + cos (13.
+ EheiPh [2 sin 20 sin2ep Ecxejl)cx + cos 6 sin it ELxeilILX1
(18)
Ev
Eh
Ph
Ecx
x
- angle of incidence measured from the perpendicular
- azimuth angle
amplitude of the incident vertically polarized wave
- phase of the incident vertically polarized wave
- amplitude of the incident horizontally polarized wave
- phase of the incident horizontally polarized wave
- arbitrary amplitude constant for coaxial spaced loop
- arbitrary phase constant for coaxial spaced loop
ELX arbitrary amplitude constant for simple loop perpendicular
to spaced loop axis
cbLx -
arbitrary phase constant for simple loop perpendicular to
spaced loop axis
Using this revised program, the free space patterns (reflected
wave neglected) were calculated for the coaxial spaced loop, the simple
Approved For Release 2001/09/0137: CIA-RDP76-00451R000200010013-1
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
loop, clockwise sense (simple loop phase advanced 900) and counterclock-
wise sense (simple loop phase advanced 270?). Patterns were calculated
at 0 = 5? (85? above the horizontal); 0 = 15? (750 above the horizontal);
0 =
25?
(65? above the horizontal);
0 =
450 (450 above the horizontal);
0 =
60?
(30? above the horizontal);
9 =
78? (120 above the horizontal); and
0 =
90?
(0? above the horizontal).
The amplitude A for the simple loop
sense function of Equation (17) was one for angles of incidence of 0 = 78?,
0 = 30?, and 0 = 45?. The value of A was set at 0. 5 for 0 = 25?, 0 = 15?,
and 0 = 5? to obtain a more readable sense pattern at these higher angles
of signal elevation.*
The polarization conditions considered were:
Polarization Polarization Description
Ev = 1
Eh = 0
, Pv = 0?
, Ph = 0?
Ev = O. 9 , Pv = 0?
Eh = O. 4 ,
Ev = 1
Eh = 1
Ev = 1
Eh = 1
, Pv = 0?
, Ph = 00
, Pv = 45?
, Ph = 0?
Ev = O. 4 ,
Eh = O. 9 ,
Ev = 0
Eh = 1
, Pv = 0?
0?
Ev = 1 ,
Eh = 0. 707, Ph = 90?
Vertical
Mixed Linear
Mixed 45? Linear
Mixed Elliptical
Mixed Linear
Horizontal
Eliptical (almost circular)
The patterns obtained at horizontal incidence (0 = 90?); 12? above
the horizontal (0 = 78?); 30? above the horizontal (0 = 60?); and 450 above
the horizontal (0 = 45?) for the coaxial spaced loop and simple loop are
given in Figure 3. The inverted coaxial spaced loop patterns and the
inverted simple loop patterns are plotted on the same polar diagram with
*The experimental work of Section 4.2 indicated, however, that one value
of sense injection produced useful sense patterns for all signal angles of
elevation up to and including 85?.
Approved For Release 2001/09/6? : CIA-RDP76-00451R000200010013-1
1.-?1.001.000Z000t11.91700-9/dati-VIO : C0/60/1?00Z aseeieu JOd peACLICIdV
0 = 78?
(12? ABOVE THE
HORIZONTAL)
0 = 60?
(30? ABOVE THE
HORIZONTAL)
= 45?
(45? ABOVE THE
HORIZONTAL)
SPACED LOOP
? ? ? ? - SIMPLE LOOP
Vertical Polarization
EV = 1; Pv = 0?
EH = 0; PH = 00
Linear Polarization
EV = ? 9; PV 0?
EH = .4; PH = 0?
Linear Polarization
EV = 1; PV = 00
EH = 1; PH = 00
Elliptical Polarization
EV = 1; PV = 00
EH = 1; PH = 45?
Linear Polarization
EV = .4; PV = 0?
EH = .9; PH = 00
Horizontal Polarization
EV = 0; PV = 00
EH = I; PH = 00
= 90?
(0? ABOVE THE
HORIZONTAL)
All Polarizations
0 = 45?
(45? ABOVE
THE HORIZONTAL)
Elliptical Polarization
EV = I; PV = 0?
EH = .707; PH = 900
FIGURE 3
SIGNAL AT 0? FOR ALL PATTERNS
E v = AMPLITUDE OF VERTICAL COMPONENT
Eh = AMPLITUDE OF HORIZONTAL COMPONENT
p v = PHASE OF VERTICAL COMPONENT
Ph = PHASE OF HORIZONTAL COMPONENT
COAXIAL SPACED LOOP AND SIMPLE LOOP PATTERNS AS A FUNCTION OF SIGNAL
POLARIZATION AND ANGLE OF INCIDENCE
19
1.-?1.001.000Z000t11.91700-9/dati-VIO : C0/60/1?00Z aseeieu JOd peACLICIdV
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
the spaced loop as a solid line and the simple loop as a dashed line. All
of the patterns at 0 = 900 are not given because only the vertical component
will exist at this angle of incidence. The signal is at 00 azimuth for all
patterns.
The DF and sense patterns obtained are given in Figures 4, 5, 6,
7, 8, and 9 with each illustration giving the patterns for one angle of inci-
dence. The patterns of these six figures are inverted plots with the pat-
tern minimum on the outside of the polar diagram as in Figure 3. The
coaxial spaced loop pattern (the solid line) and the simple loop pattern
(the dashed line) are plotted together. The clockwise sense pattern, the
counterclockwise sense pattern, and the sense pattern with 90? deflection
plate switching are given. The patterns at 0 = 90? (0? above the horizontal)
are not given because they are similar to the vertical polarization patterns
(Ev = 1, Pv = 0, Eh = 0, and Ph = 0?) at 0 = 78? (12? above the horizontal).
Lt will be noted that all, of the coaxial _spaceclloop antenna patterns
in Figure?s-raliOugh 9 have one pair of nulls which remain in the same
pltrgtrion--for all signal yolaiizations and angles of incidepce. (This pair
oT1l1 ned th-e-S*13aCed lOop ) The simple loop (with the plane
of the loop chosen parallel to the loops of the coaxial spaced loop) has
nulls which shift in position from 90? and 270? for vertical polarization
to 0? and 180? for horizontal polarization. The simple loop nulls agree in
position with the unwanted nulls (loop nulls) of the coaxial spaced loop pat-
tern. If elliptical or circular polarization is present, both the loop nulls
of the coaxial spaced loop pattern and the simple loop nulls are blurred
(the null depth is decreased). In practice, with skywave signals, the shift-
ing in position and blurring of the loop nulls of the coaxial spaced loop
pattern serves to identify them while the spaced loop nulls are identified
by the fact that their position does not change significantly.
The significance of the patterns of Figures 3 through 9 was, first,
the coaxial spaced loop yields bearing information for all signal polariza-
tions for angles of incidence of 5? to 90? (angles of arrival of 85? to 0?).
Second, the sense system works for all conditions. Third, deflection plate
switching of the sense pattern will simplify operator pattern interpretation.
4. 1. 5 Experimental Investigation
The experimental investigation involved the design, construction,
and evaluation of three breadboard HF coaxial spaced loop antennas as
discussed in the three quarterly reports. (3, 4, 5) All of the breadboard
antennas were constructed using brass and copper materials with soldered
joints. The investigation of coaxial spaced loop antennas with multiturn
Approved For Release 2001/09/&: CIA-RDP76-00451R000200010013-1
1.-?1.001.000Z000t11.91700-9/dati-VIO : C0/60/1?00Z aseeieu JOd peACLICIdV
JIJUUCU LULJJ
?Simple Loop
Clockwise Sense
C6tinterclockwise
Sense
Sense With
Deflection Plate
Switching
Ev = Amplitude of Vertical Component
Pv = Phase of Vertical Component
Vertical Polarization
E v =I ;
EH =0; PH =0?
Linear Polarization
Ev =.9 ; Pv =00
EH =.4 ; PH =0?
Linear Polarization
Ev =I; 0v=0?
EH = I ; PH _CO
EH= Amplitude of Horizontal Component
PH = Phase of Horizontal Component
Elliptical Polarization
Ev =I ; Pv =0?
EH = I ; PH = 45?
Linear Polarization
E v = .4 ; Pv =0?
EH = ; PH =0?
Horizontal Polarization
Ev =0;
EH = ; PH=0?
Signal at 00 at all Patterns
FIGURE 4.
COAXIAL SPACED LOOP AND SENSE PATTERNS ASA FUNCTION OF SIGNAL POLARIZATION
AT e = 78? (12? ABOVE THE HORIZONTAL)
21
1.-?1.001.000Z000t11.91700-9/dati-VIO : C0/60/1?00Z aseeieu JOd peACLICIdV
1.-?1.001.000Z000t11.91700-9/dCltl-VIO : CO/60/1.00z aseeieu -10d peACLICIdV
Spaced Loop
?Simple Loop
Clockwise Sense
Canterclockwise
Sense
Sense With
Deflection Plate
Switching
Ev = Amplitude of Vertical Component
Pv = Phase of Vertical Component
Vertical Polarization
Ev = I ; PI" =0?
EH =0; PH =0?
Linear Polarization
E v =.9 ; Pv r00
EH =.4 ; PH = 0?
Linear Polarization
Ev =I ; Pv =0?
EH =1 ; PH =00
EH= Amplitude of Horizontal Component
PH = Phase of Horizontal Component
Elliptical Polarization
E v = I ; Pv = 0?
EH = I ; PH45
Linear Polarization
E v = .4 ;
EH = ?9 ; PH =0?
Horizontal Polarization
Ev =0; Pv = 00
EH = I ; PH= 0?
Signal at 0? at all Patterns
FIGURE 5 .
COAXIAL SPACED LOOP AND SENSE PATTERNS AS A FUNCTION OF SIGNAL POLARIZATION
AT 0 = 60? (300 ABOVE THE HORIZONTAL)
22
1.-?1.001.000Z000t11.91700-9/dCltl-VIO : CO/60/1.00z aseeletliOd peAoiddv
1.-?1.001.000Z000t11.91700-9/dCltl-VIO : ?0/60/1?00Z aseeieu -10d PeACLICidV
Spaced Loop
?Simple Loop
Clockwise Sense
Canterclockwise
Sense
Sense With
Deflection Plate
Switching
Ey = Amplitude of Vertical Component
Py = Phase of Vertical Component
Vertical Polarization
Ey = I ;
EH=0; p H=? ?
Linear Polarization
Ey?Py =0?
EH =.4 ; PH =0?
Linear Polarization
Ey =I ; Py=0?
E =1 P
H H =0?
EH= Amplitude of Horizontal Component
PH = Phase of Horizontal Component
Elliptical Polarization
Ey =I ;
EH = I ; PH =45?
Linear Polarization
Ev? = 4 ?, P =0?
v
EH = '9 ; PH =0?
Horizontal Polarization
Ey =0; Py = 0?
EH= I ; PH = ?
0
Signal at 00 at all Patterns
FIGURE 6 .
COAXIAL SPACED LOOP AND SENSE PATTERNS ASA FUNCTION OF SIGNAL POLARIZATION
AT e =450 (450 ABOVE THE HORIZONTAL)
23
1.-?1.001.000Z000t11?91700-9/dCIU-VIO : CO/60/1.00Z aseeieu -10d PeACLICIdV
1.-?1.001.000Z000t11.91700-9/dati-VIO : C0/60/1?00Z aseeieu JOd peACLICIdV
Spaced Loop
Simple Loop
Clockwise Sense
Canterclockwise
Sense
Sense With
Deflection Plate
Switching
Ev = Amplitude of Vertical Component
Pv = Phase of Vertical Component
Vertical Polarization
E v = I ; !Dv =0?
EH =0; PH =0?
Linear Polarization
E v =.9 ; Pv = 0?
EH =.4 ; PH =00
Linear Polarization
Ev =I ; Pv =0?
E = I P
H ;H = 0?
EH= Amplitude of Horizontal Component
P = Phase of Horizontal Component
Elliptical Polarization
E = I -7 =
EH = I ?7 P H45
Linear Polarization
E v = .4 ; Pv =0?
EH = '9 ; PH=0?
Horizontal Polarization
Ev =0; Pv =
EH = I ; H
P=0?
Signal at 00 at all Patterns
FIGURE 7.
COAXIAL SPACED LOOP AND SENSE PATTERNS ASA FUNCTION OF SIGNAL POLARIZATION
AT 0 = 25? ( 65? ABOVE THE HORIZONTAL)
24
1.-?1.001.000Z000t11.91700-9/dati-VIO : C0/60/1?00Z aseeieu JOd peACLICIdV
1.-?1.001.000Z000t11.91700-9/dati-VIO : C0/60/1?00Z aseeieu JOd peACLICIdV
nnrari I nnn
?Sir;; Loop
Clockwise Sense
CO1interclockwise
Sense
Sense With
Deflection Plate
Switching
Ev = Amplitude of Vertical Component
Pv = Phase of Vertical Component
Vertical Polarization
E = I ; Pv =0?
EH =0; PH=0?
Linear Polarization
E=.9 ; =0?
VV
EH =.4; PH =00
Linear Polarization
Ev =I; Pv=0?
E =I ;
H PH =0?
EH= Amplitude of Horizontal Component
PH= Phase of Horizontal Component
Elliptical Polarization
Ev =I; Pv =00
EH = I ?7 P H45
Linear Polarization
E v = .4 ; Pv=0?
EH = ?9 ; PH=0?
Horizontal Polarization
Ev =0; Pv =0?
EH= 1 ; PH =0?
Signal at 00 at all Patterns
FIGURE 8 .
COAXIAL SPACED LOOP AND SENSE PATTERNS ASA FUNCTION OF SIGNAL POLARIZATION
AT e = 150 (75? ABOVE THE HORIZONTAL)
Z5
1.-?1.001.000Z000t11.91700-9/dati-VIO : C0/60/1?00Z aseeieu JOd peACLICIdV
Spaced Loop
Simple Loop
Clockwise Sense
Canterclockwise
Sense
Sense With
Deflection Plate
Switching
Ev = Amplitude of Vertical Component
Pv = Phase of Vertical Component
Vertical Polarization
E =I ; Pv =0?
EH =0; PH=0?
Linear Polarization
E =.9 ; Pv =0?
EH "2.4 ; PH =0?
Linear Polarization
Ev =I; Pv=0?
EH -I.. PH -C?
EN= Amplitude of Horizontal Component
PH = Phase of Horizontal Component
Elliptical Polarization
Ev =I ; Pv =0?
EH =I ? P H45
Linear Polarization
E v = .4 ; Pv =0?
EH = ?9 ; PH=0?
Horizontal Polarization
Ev =0; = 0?
EH 2 I ; PH= 0?
Signal at 00 at all Patterns
FIGURE 9.
COAXIAL SPACED LOOP, AND SENSE PATTERNS AS A FUNCTION OF SIGNAL POLARIZATION
AT e = 5? (85? ABOVE THE HORIZONTAL)
26
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
loops was pursued in the first two breadboard models to the extent neces-
sary to determine the feasibility of this approach. The use of multiple
turn loops significantly reduces the dimensions of a coaxial spaced loop
for a given sensitivity. The third model was then designed and constructed
based upon the anticipated design for the final advanced development/
feasibility model. Evaluation and modification of this third model was con-
tinued until as many design parameters for the final model could be final-
ized as possible.
The first model of the breadboard HF coaxial spaced loop antenna
is illustrated in Figure 10. This model has 14-in, square loops spaced
approximately 40 in. apart. Each loop was wound with five closely spaced
turns. As discussed in Quarterly Report No. 1, (3)the pattern quality of the
spaced loop mode of the antenna was only fair. The effective volume of
the antenna was approximately 1/3 of the anticipated required volume for a
10 microvolt per meter sensitivity. (Effective volume is defined as loop
area times number of turns times spacing..) The measured sensitivity
was approximately 30 microvolts per meter using the CW method.
The second model breadboard HF coaxial spaced loop antenna is
shown mounted on a modified AN/PRD-7 and 8 pedestal in Figure 11.
This model had 24-in, square loops spaced approximately 54 in. apart.
Each loop was wound with three turns spaced 1/8 in. apart. The model
was based upon the third model which was being designed at the time.
The construction technique was believed adequate only for impedance
measurements; however, limited field tests were performed. Sensitivity
approached the design goal while the pattern quality was again fair with
some dipole distortion evident. (3)
The third model of a breadboard HF coaxial spaced loop antenna
as shown in Figure 12 was constructed with increased precision as thought
necessary to meet the DF and sensitivity requirements. The loops, as in
the second breadboard model, are 24 in. square spaced approximately
54 inches. The individual loops are wound with three turns spaced
approximately 1/8 in. apart. The antenna is shown mounted on a modified
AN/PRD-7 and 8 pedestal in Figure 13. The third model contained all
the remote control functions anticipated for the final model.
It will be noted that all of the breadboard antennas discussed use
twin gaps or balanced gap shielded loops. Because of the success with
the balanced gap arrangement as compared to the single gap antenna in
?work under Contract DA 28-043 AMC-01633(E), (7' 14,J5) single gap arrange-
ments were not considered in this development. The work in the referenced
reports with VHF spaced loop antennas had indicated in comparison tests
that the twin or balanced gap configuration was superior to the conventional
Approved For Release 2001/09/0S : CIA-RDP76-00451R000200010013-1
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
Cs.1
C3`
LC)
\
FIGURE 1 0
Approved For Release 2001/04/03 : CIA-RDP76-00451R000200010013-1
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
FIGUR E 11
,A DKOARD 1fF COAXIAL SPACED LOOP ANTENNA (MODEL 2)
MOUNTED ON THE AN/ PRD-7 AND 8 PEDESTAL
Approved For Release 2001/09/(03 : CIA-RDP76-00451R000200010013-1
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
Approved For Release 2001/09A : CIA-RDP76-00451R000200010013-1
FIGURE 12
0
0
0
PL,
cf)
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
FIGURE 13
BREADBOARD HF COAXIAL SPACED LOOP ANTENNA (MODEL 3)
MOUNTED ON THE .AN/PRD-7 AND 8 PEDESTAL
31
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
single gap arrangement. The relative position of the two gaps with respect
to the support mast was important in the VHF antennas. However, there
was no significant difference in the HF spaced loop work to date between
placing the gaps on the top and bottom or on the sides.
The third breadboard model with various modifications has served
as the basis for design of the final advanced development/feasibility model
discussed in subsequent sections. A description of the antenna, discussions
of modifications, and a description of the evaluation of the antenna may be
found in the three quarterly reports. (3,4, 5) The evaluation has included
skywave bearing accuracy tests which were partially reported in Quarterly
ReportNo. Z. (4) All skywave bearing data obtained with the third bread-
board model are presented in Section 4. 3. 3. 5 of this report so that it may
be compared with the data obtained with the final advanced development/
feasibility model.
4. 2 Phase Il - Design Phase
The design phase has been covered in the previous reports for this
program. (3, 4, 5) The designwas based upon the successful third bread-
board model with a change to welded aluminum construction and a change
in design to allow disassembly of the final model to produce a portable HF
spaced loop antenna. The weight of the materials used in this first model
is conservative, resulting in a total weight which is more than necessary.
Other improvements have become obvious as this first unit was constructed
and evaluated. A number of possible design improvements are given in
Section 4. 3. 5.
The design of the advanced development/feasibility model of an HF
spaced loop antenna has included the antenna structure, the rotation pedes-
tal, and the interconnecting cables associated with the system. The equip-
ment has been designed to be compatible with the DF indicator for the
AN/TRD-20, or equivalent, and the radio receiver R-901/PRD. Neither
of these equipments was furnished during the program, and the design was
based on available information on the equipments.
The third model of the breadboard antenna was continuously updated
throughout the design phase to incorporate the changes necessitated by a
practical design. At the end of the design phase, the breadboard antenna
was essentially the same as the anticipated final advanced development/
feasibility model with the exception of materials and the provision for
disassembly.
It should be pointed out that several parameters of the HF spaced
loop are difficult to specify. Probably the most critical aspect of the
Approved For Release 2001/09/0-ia. CIA-RDP76-00451R000200010013-1
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
spaced loop is obtaining a balance between the two sides of the antenna.
This may be equated to having equal impedance between the two loop ele-
ments of the antenna. It is estimated that the impedance of the two sides
of the antenna as measured at the center crossover point must be equal
within 0. 1 percent. This exceeds the measurement accuracies of most
impedance bridges in the HF frequency range. The parameters given in the
improved design section include the mechanical and electrical tolerances
believed necessary to meet this requirement.
4. 3 Phase III - Equipment Construction and Evaluation
4. 3. 1 Introduction
The advanced development/feasibility model of the HF spaced loop
antenna was designed and constructed as part of a portable HF spaced loop
direction finder set (or system). The system will be discussed initially,
followed by discussions of the individual components with emphasis on the
antenna. The receiver and DF indicator specified by the U. S. Army were
not furnished. Substitute equipments discussed in subsequent sections
were used to complete the system.
4. 3.2 Description of the HF Spaced Loop Direction Finder Set
4. 3. 2. 1 System Description
The components of the HF spaced loop direction finder set are
detailed in Table 1. The modifications of components to be furnished by
the U. S. Army are given. These modifications are detailed in the section
covering the individual component. The pedestal modification is complete
on the unit shipped, but the details of the minor modifications are given in
Section 4. 3. 2. 3 so that other units may be modified if desired.
The equipment listed in Table 1 furnished by this laboratory is
shown in the transit bags in Figure 14. The largest rectangular canvas
covered case in Figure 14 contains the disassembled antenna and mast
extension sections. The small rectangular canvas transit case contains
the control unit for the pedestal and the antenna and the control unit to
indicator cable. The pedestal, 100-ft control cable, and compass are
enclosed in a transit carrying bag similar to the type normally used with
the AN/PRD-7 and 8 system.
The components of the portable HF spaced loop DF set furnished by
this laboratory have a total weight of 144. 5 lb. Table 2 gives the transit
bag number, transit bag nomenclature, and details the components con-
tained within each transit bag,
Approved For Release 2001/09/0i CIA-RDP76-00451R000200010013-1
1.-?1.001.000Z000t11.91700-9/dati-VI3 : C0/60/1?00Z aseeieu JOd peACLICIdV
TABLE 1'
List of Components for Portable HF Spaced Loop Direction Finder Set
Equipment Quantity Source Modifications
Advanced development/ feasibility >
-0
model of an HF spaced loop antenna 1 SwRI None TS
n
SwRI 0
None
<
M
Mast extensions 2 a
-II
0
n
Pedestal (modified AN/PRD-7&8 type) 1 SwRI - X
purchased m
E
from AEL As detailed in section 4.3.2.3 a)
to
CD
n.)
Pedestal control cable 1 SwRI None o
o
_.
a
to
Pedestal and antenna control unit 1 SwRI None o
(.4
Control unit to indicator cable 1 SwRI None 0
X
AN/ TRD-20, AN/ TRQ-23, or 1 U.S. Army a) Verify wiring of the unit for the 0
-0
AN/ PRD-5 DF indicator recommended interconnect -4
co
schematic, Figure 15.
O'
b) Improve overall performance for.D.
tri
spaced loop as detailed in sectior
4.3.2.5.1 o
o
o
n.)
R-901/PRD receiver 1U. S. Army Improve video detector linearity ana
set video DC level for DF indicator
as necessary as detailed in section ?
4.3.2.5.2 ce
_.
AN/ PRD-78z8 battery pack or equivalent 1 U. S. Army None
Power cable to indicator 1 U. S. Army As required with type indicator used
Video cable - receiver to indicator 1 U. S. Army Per Figure 15 and actual receiver used.
FIGURE 14
COMPONENTS OF PORTABLE HF SPACED LOOP DIRECTION FINDER SET
CONSTRUCTED BY SOUTHWEST RESEARCH INSTITUTE
SHOWN IN TRANSIT BAGS
1.-?1.001.000Z000t11.91700-9/dati-VIO : C0/60/1?00Z aseeieu JOd peACLICIdV
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
TABLE 2
Transit Bag Nomenclature, Contents, and Weights
For the HF Spaced Loop DF Set
Transit Bag Number
and Nomenclature Part Name Qty.
Unit
Wt.
Total
Wt.
Bag 1 - Antenna, HF
Loop assembly
2
3.75
7.5
spaced loop DF set Yr
Boom element assembly
2
2.25
4.5
Electronics assembly
1
9.0
9.0
Loop braces
8
.5
4.0
Mast extensions
2
2.5
5.0
Transit bag
1
27.0
27.0
TOTAL WEIGHT
57 0 lbs.
? Bag 2 - Pedestal,
tripod, compass,
100-ft. control cable
Modified AN/PRD-7&8
pedestal
100-ft. pedestal control
1
49.0
49.0
for DF set
cable
1
18.0
18.0
Compass
1
.5
.5
Transit bag
1
7.5
7.5
TOTAL WEIGHT
75 0 lbs.
Bag 3 - Control unit
Control unit for the HF
for the HF spaced loop
spaced loop DF set
1
9.5
9.5
DF set
Control unit to indicator
cable
1
.5
.5
Transit bag
1
2.5
2.5
TOTAL WEIGHT
12 5 lbs.
" 7(42.41/41,,-
Approved For Release 2001/09/0336: CIA-RDP76-00451R000200010013-1
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
If all components of the system listed in Table 1 were available,
then the recommended interconnection schematic of Figure 15 is applicable.
Figure 15 also gives the schematic of the mast extensions used between
the pedestal and antenna. The shielding and ground circuits are necessary
to avoid stray pickup on the control leads. The mast extensions used with
the VHF spaced loop developed under Contract DA 28-043 AMC-01633(E)
are similar; therefore, the masts are keyed so that both mate with the
pedestal but so that the VHF and HF antennas cannot be placed on the wrong
mast.
The interconnection cables associated with the DF indicator and the
R-901/PRD receiver are based on available information. However, avail-
able schematics of DF indicators of the AN/TRD-20, AN/TRQ-23, or
AN/PRD-5 types vary slightly in circuitry. For this reason, it is suggested
that Figure 15 be compared to the particular unit which will be used by the
U. S. Army. Control cables distinctly associated with equipments not
furnished the contractor are not included for this reason.
In the evaluation of the HF spaced loop antenna, an R-390A/U
receiver with a separate outboarded IF amplifier and DF video detector
was used in place of R-901/PRD receiver. Information on the IF amplifier
and DF video detector is given in Section 4.3.2. 5. Z.
4. 3.2. 2 Advanced Development/Feasibility HF Spaced Loop Antenna
The advanced development/feasibility model of an HF spaced loop
antenna represents the primary emphasis of this program. This section
will emphasize a description of the antenna in the form delivered to the
U. S. Army. Critical specifications will be given in the section on an
improved design (Paragraph 4. 3. 5).
The advanced development/feasibility model of the HF spaced loop
antenna, Serial No. 1, is shown in the transit case in Figure 16. Included
in this transit case with the disassembled antenna components are the two
mast sections. The canvas transit case is filled with foamed polyurethane
with slots to retain the antenna components.
The components of the HF spaced loop antenna are shown in front of
the transit bag in Figure 17. The antenna is shown assembled in Figure 18.
The break-apart connectors between the loops, boom elements, and center
electronics housing are identical to those used on the VHF spaced loop
antennas developed under Contract IDA 28-043 AMC-01633(E) as discussed
in References 14 and 18. Quick disconnect clamps are used to hold the
five major parts of the antenna together when assembled. Braces are
Approved For Release 2001/09/?S : CIA-RDP76-00451R000200010013-1
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
ft
ft
OSNS M.,

riath 'aiv'3
ro ra -I-1
.5_ ; (7,77ZZ H-71,
I-Fkg,011 1 _'QrNv9I I7
tC/ Q
,/,29-...."
1 :1.,
VI tfl 7VA,D/5. ,,
, -- I 0,,,,,
,,
I*
*-I I s, ?,,, 1 I * *
el
JOA w,Z? tot -=.
22 6' is.
T1 2.,;.
tO0
ft
kilZ dLI.OZ-37//E,SGY
k 2 (WS)SLZ.02-39I/E-SPv
ft
0.
z
ft
co
ft
ft
ft
ft
?)1
01 0 tr)
2 2
ft 'IC
kD
ft
z
ft
ft
ft
ci
?),
ft
ft
110
LU
ft
10
ft
LI
ft
ci
ft
ft
a
ft
4.1
00
ft
ft
'8.9-32//?-SI10/
SD?8-g.9//E-SYV
t
Lift di, -6,39/ tE-SIN
Lift5,S.-e910//F-0000
ft
ft
Approved For Release 2001/09/OV: CIA-RDP76-00451R000200010013-1
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
FIGURE 16
THE DISASSEMBLED PORTABLE HE SPACED LOOP ANTENNA
TN THE TRANSIT CASE
Approved For Release 2001/0i/b3 : CIA-RDP76-00451R000200010013-1
FIGURE 17
THE DISASSEMBLED PORTABLE HF SPACED LOOP ANTENNA
1.-?1.001.000Z000t11.91700-9/dati-VIO : C0/60/1?00Z aseeieu JOd peACLICIdV
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
Approved For Release 2001/04/63 : CIA-RDP76-00451R000200010013-1
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
installed between opposing corners of the two loops to establish the required
spaced loop geometry. As discussed in Paragraph 4.3. 5, improved flange
surfaces between the loops, boom elements, and center electronics housing
probably would establish the required geometry without bracing. The
mating parts of the antenna are marked with a code system so that they
may be quickly assembled. The loops and boom elements are not inter-
changeable and are keyed so that they cannot be installed incorrectly.
The antenna is shown mounted 10 ft above the ground using the two
2-1/2-ft mast extension sections on the modified AN/PRD-7 and 8 pedestal
in Figure 19.* This is the recommended operational configuration. The
10-ft height appears necessary to reduce site error from the single control
cable. (3) Although a ground stake may be seen immediately below the
center of the pedestal in Figure 19, physical grounds of the pedestal were
avoided because of the portable requirement.
The schematic of the advanced development/feasibility model of an
HF spaced loop is shown in Figure 20. The three-turn loops are fed
through the boom assembly to the crossover switching assembly at the
center of the antenna. The purpose of the crossover switching assembly
is to reverse the antenna from a spaced loop mode to a simple loop mode
by changing the connection between the loops from parallel opposition to
parallel aiding. The output of the crossover switching network is fed to
the tuning network and the FET source follower amplifier of Figure 21.
The balanced broadband transistor amplifier of Figure 22 is used to raise
the signal level so that the effects of stray pickup on the control cable will
be eliminated. A balanced to unbalanced balun (T-1) is included as part
of the broadband amplifier of Figure 22.
Tuning of the antenna is accomplished using the varactor diodes
shown in Figure 21. The diodes tune the antenna inductive reactance over
the lowest frequency band. For the higher frequency bands, the antenna
is shunted with inductance to decrease the effective inductance.
The control circuitry is straightforward. The series voltage regu-
lator of Figure 23 provides +16 volts DC ?0. 5 volt DC for the amplifiers
for primary supply variations of +18 to +32 volts DC. Sensitivity is inde-
pendent of the battery pack voltage limitations for the limits given.
The circuit of Figure 23 differs slightly from the circuit in the
antenna shipped to the U. S. Army. The 10-ohm resistors, R-704 and
R-705, were not included in the unit but are recommended to prevent
shunt circuit damage to the regulator circuit.
It is essential that the control cable within each mast section be wired
in accordance with Figure 15.
Approved For Release 2001/09/034. CIA-RDP76-00451R000200010013-1
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
FIGURE 19
PORTABLE I-IF SPACED LOOP ANTENNA ON
TI-IE MODIFIED ANJPRD-7 A.ND 3 PEDESTAL
43
Approved For Release 2001/09/03 : CIA-RDP76-00451R000200010013-1
TEST POINTS
1 R707
J703
C71.5 t_E-112-771 470;c11-",:y 1
? ?I
' 1
- P704 J708R704J704
2705 >>.J 705
R7OT.> J707
2702
RFC-701
k701.
REED SWITCH
'01 cRossoveR
/2550
SFC-702
SENSE NETwoRK,;ENSTT, P709 >> .1 09
REED SvVITC-1-1
EAST
LOc P
ELEMENT
07E0 0721
.01
? ?
CfRouND
OW SENSE
EAST
BOOM
CCC
LI0704
.o 1
simPLE LOOP
CCW SENSE
0711
0703
?--,C,;f :7
I 151 21 4 ITB-70z
ELECTRoNICS
CHASSIS
T
710