TimeSource 3500
GPS Primary Reference Source
097-72050-01
Issue 7: August 2003
FCC Regulatory Notice
Warning: This equipment generates, uses, and can radiate
radio frequency energy, and if not used in accordance with
the instruction manual, may cause interference to radio
communications. It has been tested and found to comply with
the limits for a Class A computing device pursuant to Subpart
B of Part 15 of FCC rules, which are designed to provide
reasonable protection against such interference when
operated in a commercial environment. Operation of this
equipment in a residential area is likely to cause interference
in which case the user at his own expense will be required to
take whatever measures may be required to correct the
interference.
Symmetricom, Inc.
2300 Orchard Parkway
San Jose, CA 95131-1017
http://www.symmetricom.com
Copyright © 2003 Symmetricom, Inc.
All rights reserved. Printed in U.S.A.
Symmetricom is a registered trademark of Symmetricom, Inc. BesTime, DCD, and TimeSource are
trademarks of Symmetricom, Inc. All other product names, service marks, trademarks, and registered
trademarks used in this document are the property of their respective owners.
2 TimeSource 3500
097-72050-01 Issue 7: August 2003
Contents
Acronyms and Abbreviations
AIS alarm indication signal
ANSI American National Standards Institute
DS1 digital signal, level 1 (1.544 Mb/s)
ESD electrostatic discharge
ESF extended superframe
GPS Global Positioning System
LOS loss of signal
MDEV mean time deviation
pps pulse per second
PRS primary reference source
RO remote oscillator
RU rack unit (1.75 in.)
SSM synchronization status messaging
T1 digital transmission (1.544 Mb/s)
TDEV time deviation
TOD time of day
UTC Universal Coordinated Time
TimeSource 3500 3
Contents
097-72050-01 Issue 7: August 2003
What’s New in This Manual
This issue of the TimeSource 3500 user manual has the following
changes from the previous issue:
• Added “Antenna Installation and Lightning Protection”,
“Startup”, “Bridging/Holdover Behavior” and “Time Figure of
Merit” sections to Chapter 1.
• Removed TimeScan Craft connection key (020-46700-001)
from system equipment lists in Chapter 2.
• Added wall antenna L1 outdoor lightning suppressor kit (09372050-93) to Wall Antenna kit listing in Chapter 2.
• Added wall antenna lightning suppressor kit (093-72050-94)
to Wall Antenna kit listing in Chapter 2.
• Added information on installing wall antenna indoor lightning
suppressor kit to Procedure E, Wall Antenna Installation, in
Chapter 3.
• Added information on installing wall antenna outdoor lightning suppressor kit to Procedure E, Wall Antenna Installation,
in Chapter 3.
• Added section on TimeWizard software installation application to Chapter 3.
• Added Procedure I, TimeWizard Installation and Operation,
to Chapter 3.
4 TimeSource 3500
097-72050-01 Issue 7: August 2003
Contents
• Added TL1 command “RTRV-HDR” for NMA keep alive
responses.
TimeSource 3500 5
Contents
097-72050-01 Issue 7: August 2003
6 TimeSource 3500
097-72050-01 Issue 7: August 2003
Contents
Description
Overview . . . . . . . . . . . . . . . . . . . 20
Chapter 1
Global Positioning System . . . . . . . . 21
Physical Description . . . . . . . . . . . . 22
Roof Antenna . . . . . . . . . . . . . . 24
Mechanical Window Antenna . . 25
Self-Adhesive Window Antenna . . 26
Wall Antenna . . . . . . . . . . . . . . 27
Functional Description . . . . . . . . . . . 28
Overview . . . . . . . . . . . . . . . . 28
Antenna . . . . . . . . . . . . . . . . . 30
Antenna Installation and Lightning
Protection . . . . . . . . . . . . . . 30
IF Interface . . . . . . . . . . . . . . . . 32
GPS Receiver . . . . . . . . . . . . . . 32
Local Oscillator . . . . . . . . . . . . . 32
Clock Extractors . . . . . . . . . . . . 32
Power Supply . . . . . . . . . . . . . . 33
NTP TimeServer . . . . . . . . . . . . 33
Network Time Protocol Password
Activation . . . . . . . . . . . . . . 33
BesTime Ensemble Timing Generator 33
Eight Mixed E1/T1 Outputs . . . . 34
Eight Mixed T1/CCK Outputs . . . 34
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Contents
097-72050-01 Issue 7: August 2003
T1 Outputs . . . . . . . . . . . . . . . . 34
Additional T1 Outputs
(990-72050-02 Systems Only) 35
TOD Output . . . . . . . . . . . . . . . 35
IRIG-B TOD Outputs
(990-72050-05 Systems Only) 35
1 PPS Output . . . . . . . . . . . . . . 35
10 MHz Output . . . . . . . . . . . . 36
Composite Clock Outputs
(990-72050-03 Systems Only) 36
Alarm Interface . . . . . . . . . . . . . 36
Communication Ports . . . . . . . . . 36
Ethernet . . . . . . . . . . . . . . . . . . 36
Passthrough . . . . . . . . . . . . . . . 37
Alarm Programmability . . . . . . . . . 38
Startup . . . . . . . . . . . . . . . . . . . 39
Bridging/Holdover Behavior . . . . 40
Time Figure of Merit . . . . . . . . . . 42
Engineering &
Ordering
Antenna Guidelines . . . . . . . . . . . . 46
Roof Antenna Location and Cabling
Guidelines . . . . . . . . . . . . . . 48
Chapter 2
Roof Antenna Earth Ground Location
Guidelines . . . . . . . . . . . . . . 53
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097-72050-01 Issue 7: August 2003
Roof Antenna Cable Choices . . . 54
Window and Wall Antenna
Location Guidelines . . . . . . . . 56
Window and Wall Antenna
Cable Choices . . . . . . . . . . . 58
IRIG-B TOD (990-72050-05
System Only) . . . . . . . . . . . . 60
RJ-422–to–RS-232 TOD Converter 61
Shelf Considerations . . . . . . . . . . . . 62
Systems . . . . . . . . . . . . . . . . . . . . 63
Standard System (Two T1 Outputs) 64
With Eight Additional T1 Outputs 65
With Eight Additional Mixed
E1/T1 Outputs . . . . . . . . . . . 66
With Eight Additional Mixed
T1/CCK Outputs . . . . . . . . . 67
With Eight Composite Clock
Outputs . . . . . . . . . . . . . . . . 68
With Two IRIG-B TOD Outputs . . 69
Antennas . . . . . . . . . . . . . . . . . . . 70
Roof Antenna . . . . . . . . . . . . . . 71
Mechanical Window Antenna . . 72
Self-Adhesive Window Antenna . . 73
Wall Antenna . . . . . . . . . . . . . . 74
TimeSource 3500 9
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097-72050-01 Issue 7: August 2003
User-Supplied Tools and Materials . . 76
For Roof Antenna Installation . . . . 77
For Mechanical Window Antenna
Installation . . . . . . . . . . . . . . 78
For Self-Adhesive Window Antenna
Installation . . . . . . . . . . . . . . 79
For Wall Antenna Installation . . . . 80
For Shelf Installation . . . . . . . . . . 81
Outputs, Power, and Miscellaneous 82
Installation
Chapter 3
Unpacking . . . . . . . . . . . . . . . . . 86
Antenna . . . . . . . . . . . . . . . . . . . 87
Roof Antenna . . . . . . . . . . . . . . 87
Mechanical Window Antenna . . . 93
Self-Adhesive Window Antenna . . 97
Wall Antenna . . . . . . . . . . . . . . 100
Shelf . . . . . . . . . . . . . . . . . . . . . 108
Rack Mounting . . . . . . . . . . . . . 108
Power and Signal Cabling . . . . . 109
Frame Ground . . . . . . . . . . . . 111
Power . . . . . . . . . . . . . . . . . 113
Alarms Output . . . . . . . . . . . . 114
GPS Antenna . . . . . . . . . . . . 114
Additional T1 Outputs
(990-72050-02 System Only) 115
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097-72050-01 Issue 7: August 2003
Mixed E1/T1 Outputs . . . . . . 115
Mixed T1/CCK Outputs
(990-72050-07 System Only) 116
Composite Clock Outputs
(990-72050-03 System Only) 116
IRIG-B TOD Outputs
(990-72050-05 System Only) 116
1 PPS Output . . . . . . . . . . . . 118
10 MHz Output . . . . . . . . . . 118
Ethernet . . . . . . . . . . . . . . . . 119
Time of Day Output . . . . . . . . 120
T1 Reference Inputs . . . . . . . . 124
T1 Synchronization Outputs . . 125
Communication Port 1 . . . . . . 126
Communication Port 2 . . . . . . 127
Craft Port . . . . . . . . . . . . . . . 128
Power-Up . . . . . . . . . . . . . . . . . . . 129
TimeWizard . . . . . . . . . . . . . . . . . 142
Factory-Set Values . . . . . . . . . . . . . 157
TL1 Reference
Chapter 4
Conventions . . . . . . . . . . . . . . . . . 162
Command Format . . . . . . . . . . . . . 164
Response Format . . . . . . . . . . . . . . 165
Parameters . . . . . . . . . . . . . . . . . . 166
Autonomous Messages . . . . . . . . . . 171
Report Alarm . . . . . . . . . . . . . . 172
Report Event . . . . . . . . . . . . . . . 173
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097-72050-01 Issue 7: August 2003
Tasks/Commands . . . . . . . . . . . . . 174
Commands . . . . . . . . . . . . . . . . . 176
Activate User . . . . . . . . . . . . . . 177
Cancel User . . . . . . . . . . . . . . . 178
Copy Memory . . . . . . . . . . . . . 179
Delete Equipment . . . . . . . . . . . . 182
Delete User Security . . . . . . . . . . 183
Edit Communication . . . . . . . . . . 184
Edit Date . . . . . . . . . . . . . . . . . 188
Edit Equipment . . . . . . . . . . . . . 191
Enter Equipment . . . . . . . . . . . . . 201
Enter User Security . . . . . . . . . . . 203
Initialize Log . . . . . . . . . . . . . . . 204
Initialize Register . . . . . . . . . . . . 205
Initialize System . . . . . . . . . . . . . 206
Operate Alarm Cutoff All . . . . . . 207
Retrieve Alarm All . . . . . . . . . . . 208
Retrieve Alarm Equipment . . . . . . 209
Retrieve Communication . . . . . . . 211
Retrieve Condition All . . . . . . . . . 214
Retrieve Condition Equipment . . . . 215
Retrieve Equipment . . . . . . . . . . . 217
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097-72050-01 Issue 7: August 2003
Retrieve GPS Status . . . . . . . . . . 227
Retrieve Header . . . . . . . . . . . . 229
Retrieve Inventory . . . . . . . . . . . 230
Retrieve Log . . . . . . . . . . . . . . . 233
Retrieve Performance Monitoring . 234
Retrieve User Security . . . . . . . . . 250
Set Source Identifier . . . . . . . . . . 251
Troubleshooting
Chapter 5
Specifications
Chapter 6
Troubleshooting with Front Panel Items 254
Troubleshooting with Error Messages . 257
Card Replacement . . . . . . . . . . . . . 264
Repair and Return . . . . . . . . . . . . . 266
Technical Assistance . . . . . . . . . . . . 268
Sales . . . . . . . . . . . . . . . . . . . . . . 269
Manual Updates . . . . . . . . . . . . . . 270
Antennas . . . . . . . . . . . . . . . . . 272
Roof Antenna . . . . . . . . . . . . 272
Mechanical Window Antenna 272
Wall Antenna . . . . . . . . . . . . 273
Self-Adhesive Window Antenna 273
Communication Ports . . . . . . . . . 274
Port 1 . . . . . . . . . . . . . . . . . 274
Port 2 . . . . . . . . . . . . . . . . . 275
Craft Port . . . . . . . . . . . . . . . 276
TimeSource 3500 13
Contents
097-72050-01 Issue 7: August 2003
Ethernet Port . . . . . . . . . . . . . . . 277
Time of Day Outputs . . . . . . . . . 278
Network Time Protocol (NTP),
Type 4, Format 2 Driver Format 278
Cisco Systems . . . . . . . . . . . . 279
IRIG-B TOD Outputs
(990-72050-05 System Only) 280
T1 Inputs . . . . . . . . . . . . . . . . . 281
1 PPS Output . . . . . . . . . . . . . . 282
T1 Outputs . . . . . . . . . . . . . . . . 283
Standard . . . . . . . . . . . . . . . 283
Additional T1 Outputs
(990-72050-02 System Only) 284
Mixed E1/T1 Outputs . . . . . . . . 286
E1/T1 Common . . . . . . . . . . 286
E1 Outputs . . . . . . . . . . . . . . 286
T1 Outputs . . . . . . . . . . . . . . 287
Mixed T1/CCK Outputs
(990-72050-07 System Only) . 288
T1/CCK Common . . . . . . . . . 288
T1 Outputs . . . . . . . . . . . . . . 288
CCK Outputs . . . . . . . . . . . . 289
Composite Clock Outputs
(990-72050-03 System Only) . 290
10 MHz Output . . . . . . . . . . . . 291
Office Alarms . . . . . . . . . . . . . . 292
Rear Panel Contacts . . . . . . . . 292
Front Panel Lamps . . . . . . . . . 292
14 TimeSource 3500
Contents
097-72050-01 Issue 7: August 2003
Index
Front Panel Control . . . . . . . . 292
Simple Network Time Protocol . . . 293
Power . . . . . . . . . . . . . . . . . . . 294
Shelf Mechanical . . . . . . . . . . . 294
Shelf Environmental . . . . . . . . . . 295
Figures
1. Shelf . . . . . . . . . . . . . . . . . . . . 23
2. Roof Antenna . . . . . . . . . . . . . . 24
3. Mechanical Window Antenna . . 25
4. Self-Adhesive Window Antenna . 26
5. Wall Antenna . . . . . . . . . . . . . 27
6. Block Diagram . . . . . . . . . . . . . 29
7. Zone of Protection . . . . . . . . . . . 31
8. TimeSource 3500 Passthrough
Function . . . . . . . . . . . . . . . . 38
9. Antenna Field of View . . . . . . . . 49
10. Antenna Location Examples . . . 50
11. Sample Rooftop Antenna Mount 52
12. Antenna Mask Angle . . . . . . . . 57
TimeSource 3500 15
Contents
097-72050-01 Issue 7: August 2003
13. Rack Mounting Options . . . . . . 62
14. Roof Antenna-to-Shelf Cabling . . 88
15. Mechanical Window Antenna-to-Shelf
Cabling . . . . . . . . . . . . . . . . . . 94
16. Attaching the Mechanical Window
Antenna . . . . . . . . . . . . . . . . . . 96
17. Mechanical Window Antenna Pivot
Screws . . . . . . . . . . . . . . . . . . . 96
18. Self-Adhesive Window Antenna-to-Shelf
Cabling . . . . . . . . . . . . . . . . . . 97
19. Attaching the Self-Adhesive Window
Antenna to a Window . . . . . . . . 99
20. Attaching the IF Converter . . . . . 99
21. Wall Antenna-to-Shelf Cabling . . 100
22. Hole Spacing . . . . . . . . . . . . . 105
23. Wall Antenna Mounting . . . . . . 106
24. Wall Antenna Outdoor Lightning
Suppressor Mounting . . . . . . . . . . 107
25. Rack Mounting Options . . . . . . 108
26. Rear Panel Connectors . . . . . . . 110
27. Front Panel Connector . . . . . . . 110
28. Battery Connections . . . . . . . . . 111
29. Alarm Connections . . . . . . . . . 114
30. OPTIONS I/O Wire-Wrap Pin
Connections . . . . . . . . . . . . . . . 115
31. IRIG-B TOD BNC Output
Connections . . . . . . . . . . . . . . . 117
16 TimeSource 3500
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097-72050-01 Issue 7: August 2003
32. RS-422–to–RS-232 TOD Converter
Mounting Plate . . . . . . . . . . . . . 122
33. RS-422–to–RS-232 TOD Converter
Connections . . . . . . . . . . . . . . . 122
34. T1 Input Connections . . . . . . . . 124
35. T1 Output Connections . . . . . . 125
36. Command Format . . . . . . . . . . 164
37. Completed Response Format . . . 165
38. Deny Response Format . . . . . . . 165
39. Controls and Indicators . . . . . . 254
40. Front of Shelf . . . . . . . . . . . . . 265
41. NTP Type 4 Data Format . . . . . 278
42. Cisco Systems Data Format . . . 279
Tables
A. Timing Source Characteristics . . . 30
B. Ethernet 10base-T RJ-45 Connector
Pinouts . . . . . . . . . . . . . . . . . . 119
C. TOD Connector Pinouts . . . . . . . 120
D. Converter DB-25 Connector Pinouts 123
E. COM1 Pinouts . . . . . . . . . . . . . 126
F. COM2 Connector Pinouts . . . . . . 127
G. Craft Pinouts . . . . . . . . . . . . . . 128
H. Parameter Factory Settings . . . . . 157
TimeSource 3500 17
Contents
097-72050-01 Issue 7: August 2003
I. Parameter Definitions . . . . . . . . . . 166
J. Commands for Tasks . . . . . . . . . . 174
K. Front Panel Items . . . . . . . . . . . . 255
L. Message Troubleshooting . . . . . . . 257
Procedures
A. Site Survey . . . . . . . . . . . . . . . . 47
B. Roof Antenna Mounting and Cable
Connection . . . . . . . . . . . . . . . . 89
C. Mechanical Window Antenna
Mounting and Cable Connection . 95
D. Self-Adhesive Window Antenna
Mounting and Cable Connection . 98
E. Wall Antenna Installation . . . . . . . 101
F. IRIG-B TOD Output Installation . . . 117
G. RS-422–to–RS-232 TOD
Converter Installation . . . . . . . . . 121
H. Power-Up . . . . . . . . . . . . . . . . . 129
I. TimeWizard Installation and
Operation . . . . . . . . . . . . . . . . . 142
J. Card Replacement . . . . . . . . . . . 264
K. Equipment Return . . . . . . . . . . . . 267
18 TimeSource 3500
Contents
097-72050-01 Issue 7: August 2003
Description
This chapter provides an overview
of the global positioning system,
Chapter
1
and a physical and functional
description.
SSSSSSSSSSSS SSSSSSSSSS SSSSSSS
Overview
1
The TimeSource 3500 is a Primary Reference Source (PRS) that
receives and processes signals from GPS satellites, and outputs
Stratum 1 synchronization signals traceable to UTC. TimeSource
3500 applications include synchronization for central offices,
wireless base stations, transmission nodes, and other cases where
a primary reference source can improve the performance of a
telecommunications network infrastructure.
The TimeSource 3500 is also ideal for installation in environments
where receiving GPS signals is difficult. Examples of environments
hostile to GPS signals include urban canyons which have a very
limited view of the sky because of blockage from nearby buildings,
and high interference zones where GPS signals are jammed by
competing over-the-air signals.
The TimeSource 3500 creates timing outputs by ensembling
signals from several sources. The sources include GPS signals, an
onboard rubidium local oscillator, and optional T1 signals. Timing
outputs created from the ensemble are composed of the most
stable and least noisy parts of each input. The performance of the
T1 sources can be monitored and classified using standard
measures. Synchronization outputs are delivered in a framed, allones, T1 format, a 10 MHz signal, a 1 pps signal, a composite
clock format (optional), and a choice of time of day (TOD) formats.
The TimeSource 3500 minimizes timing impairments, such as
jitter and wander, that are created by network and transmission
systems. The synchronization timing is traceable to the GPS,
which provides the highest level of synchronization for telephony
networks. The TimeSource 3500 with its GPS input is a standalone office PRS. With the optional inputs ensembled, holdover is
extended if GPS signals are disrupted.
20 TimeSource 3500
Description
097-72050-01 Issue 7: August 2003
SSSSSSSSSSSS SSSSSSSSSS SSSSSSS
Global Positioning System
The United States Government developed the GPS navigation
system. It is a satellite-based, radio navigation aid designed to
provide global, all-weather, precise navigation and timing
capability to users 24 hours a day.
The satellites, circling the earth at approximately 12,550 statute
miles, are arranged in 6 orbits with 4 operational satellites in each
orbit. Each satellite has an orbital period of approximately
12 hours. This configuration assures that a minimum of
4 satellites, and as many as 12, are in view anywhere in the world
at all times.
The TimeSource 3500 tracks all satellites within its field of view.
The performance of each tracked satellite is observed and
compared to the others, and available for use in the timing
solution. A satellite with unacceptable performance data is
dropped from the timing solution.
GPS antennas must have line-of-sight access to the transmitting
satellites. Any structure that interferes with, or blocks, the view of
the satellites disrupts the reception of the signals, and can
adversely impact the timing performance of a receiver.
1
2
3
The TimeSource 3500 bridges frequent GPS outage periods with
BesTime algorithms, its ultra-stable Rubidium local oscillator and
advanced holdover technology. The technology anticipates the
outages and uses BesTime-generated predictor values to optimize
the performance of timing without direct satellite input.
TimeSource 3500 21
Description
097-72050-01 Issue 7: August 2003
4
5
SSSSSSSSSSSS SSSSSSSSSS SSSSSSS
Physical Description
1
The TimeSource 3500 consists of a shelf, a plug-in card, an
antenna, cables, hardware, and software. Optional system
configurations include eight additional T1 outputs, eight
additional composite clock outputs, two IRIG-B TOD timing
outputs, or eight mixed E1/T1 outputs.
The shelf (Figure 1) occupies two rack mounting units (RU), and
can be mounted in a 19 inch rack or a 23 inch rack. One RU
(1.75 in.) of air space above the TimeSource 3500 is required for
proper ventilation. Other than a communications connector on the
front panel, all connectors are at the rear of the shelf.
Four types of antennas are available:
• roof antenna for installation outdoors, usually on a roof
• mechanical antenna for installation indoors, mounted on a
window sill or wall for reception through a window
• self-adhesive antenna for installation indoors, adhered directly
to a window
• wall antenna for installation outdoors, through a hole in the wall
22 TimeSource 3500
Description
097-72050-01 Issue 7: August 2003
SSSSSSSSSSSS SSSSSSSSSS SSSSSSS
.
Figure 1. Shelf
Air space (required for proper ventilation)
17.25 in.
1.75 in
3.25 in
1
2
3
TimeSource 3500 23
Description
097-72050-01 Issue 7: August 2003
4
5
SSSSSSSSSSSS SSSSSSSSSS SSSSSSS
Roof Antenna
1
The roof antenna (Figure 2) is encased in weather-resistant plastic
housing for outdoor installation, usually on a roof. A single coaxial
cable carries signals and power between the antenna and the
shelf.
Figure 2. Roof Antenna
12.375 in.
1.75 in.
24 TimeSource 3500
Description
097-72050-01 Issue 7: August 2003
SSSSSSSSSSSS SSSSSSSSSS SSSSSSS
Mechanical Window Antenna
The mechanical window antenna (Figure 3) may be attached to a
window sill or wall, in any position that allows the antenna to be
moved flush against the window. The antenna can be swung away
from the window for window maintenance, and returned to its
original position.
A single length of coaxial cable carries signals and power between
the antenna assembly and the shelf.
Figure 3. Mechanical Window Antenna
Mounting Assembly
1
2
Antenna
Coaxial Cable
3
17 in.
IF Converter
Coaxial Cable
to TimeSource 3500 Shelf
(not included with
antenna assembly)
TimeSource 3500 25
Description
097-72050-01 Issue 7: August 2003
4
5
SSSSSSSSSSSS SSSSSSSSSS SSSSSSS
Self-Adhesive Window Antenna
1
The self-adhesive window antenna assembly (Figure 4) consists of
the antenna and two pieces of self-stick hook-and-loop fabric
fasteners (Velcro brand or equivalent). The hook-and-loop fabric
attaches directly to a window. Coaxial cables carry signals and
power between the antenna and the IF converter, and between the
IF converter and the shelf.
Figure 4. Self-Adhesive Window Antenna
GPS WINDOW
ANTENNA
26 TimeSource 3500
Description
097-72050-01 Issue 7: August 2003
SSSSSSSSSSSS SSSSSSSSSS SSSSSSS
Wall Antenna
The wall antenna (Figure 5) is mounted on the outside of a
building wall. The antenna attaches magnetically to the mounting
bracket. The cable from the antenna is routed through a hole
drilled in the wall. Coaxial cables carry signals and power between
the antenna and the IF converter, and between the IF converter
and the shelf.
Figure 5. Wall Antenna
1
2
Antenna Mounting Bracket
Antenna
3
Coaxial Cable
3 in.
TimeSource 3500 27
Description
097-72050-01 Issue 7: August 2003
4
5
1
SSSSSSSSSSSS SSSSSSSSSS SSSSSSS
Functional Description
Overview
Figure 6 shows the main functions of the TimeSource 3500. The
center of the TimeSource 3500 is the BesTime Ensemble Timing
Generator, which uses the BesTime algorithm to analyze the phase
and frequency relationships, individually and collectively, of the
timing sources. Each type of timing source has a particular
characteristic that gives it an advantage over other sources, as
listed in Table A.
The BesTime algorithm uses the best characteristic of each source
to produce an output signal with greater overall accuracy and
stability than any single source. The contribution of a source is
based on its deviation from the weighted average of all the
sources. The more accurate a source, the more weight it has in the
final output. Every source is under constant evaluation and its
contribution subject to periodic adjustment. The output is
essentially the best performance of the best source.
28 TimeSource 3500
Description
097-72050-01 Issue 7: August 2003
SSSSSSSSSSSS SSSSSSSSSS SSSSSSS
Figure 6. Block Diagram
Clock input & dc
power to antenna
Antenna
input
Optional sources
T1 Span
Input #1
T1 Span
Input #2
–48 V A
–48 V B
IF
Interface
Local
Oscillator
Clock
Extractor
Clock
Extractor
Power
Supply
processor
Ensemble
Generator
Power to
shelf
Alarm
Interface
Micro-
BesTime
Timing
Alarms
COM Ports
Ethernet Port
Status Lamps
T1 Output A
T1 Output B
1 pps Output
TOD Output
10 MHz Output
8 Composite
Clock Outputs
8 mixed E1/T1
Outputs
2 IRIG-B
Outputs
1
2
3
8 T1 Outputs
8 mixed T1/CCK
Outputs
Optional outputs
TimeSource 3500 29
Description
097-72050-01 Issue 7: August 2003
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5
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Table A. Timing Source Characteristics
1
Source Characteristic
Local Oscillator Short term stability
T1 Line Intermediate term stability
GPS Signal Long term stability
Antenna
The antenna types include a roof antenna, mechanical window
antenna, self-adhesive window antenna, or wall antenna. All
antennas include a GPS receiver, amplifier, and intermediatefrequency (IF) downconverter.
The GPS Receiver extracts a clock signal from the GPS satellite
signals. The receiver can process the signals from all satellites in
view, while simultaneously using the Earth location of the receiver
and other factors to determine an accurate clock signal.
An amplifier provides signal gain.
The downconverter converts the L1-band GPS signal to IF for
long-distance transport on the coaxial antenna cable. The antenna
cable provides current from the shelf to the antenna, and
transports GPS satellite IF signals from the antenna to the shelf.
Antenna Installation and Lightning Protection
The TimeSource 3500 standard wall antenna kits do not include
lightning protectors. When the antenna is installed on the side of
the building, the antenna is in the zone of protection and is
protected from lightning strikes as described in the Standard for
the Installation of Lightning Protection Systems (NFPA 780), 2000
edition.
30 TimeSource 3500
Description
097-72050-01 Issue 7: August 2003
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