IFR2975 Training Course

1
IFR-2975Training Course

• 2975

• WWW.P25.COM
• WWW.IFRSYS.COM

2
IFR-2975 Training Course Outline

• P25 Technology Basics
• 2975 Overview
• Basic Operation
• Functional Test Screens
• Minimizing Measurement Errors
• Spectrum Analyzer Measurements

3
Section 1 - P25 Technology Basics

• Spectral Efficiency
• Analog to Digital Conversion
• FM vs. C4FM CQPSK
• CAI (Common Air Interface)
• Impacts on Measurement Methods

4
Effects of Modulation Techniques
FM
C4FM
CQPSK
Analog Systems 25 kHz
Project 25 Phase 1 12.5 kHz
Project 25 Phase II 6.25 kHz
5
Analog vs. Digital
2800 bits/s error correction
Voice
2400 bits/s signaling
4400 bits/s voice 20 ms of speech 88 bits of
information to be transmitted over the radio link
Signaling
Total 9600 bits/s
1 25 kHz Channel
2 x 12.5 kHz Channels
6
How is Analog Converted to Digital?

• Project 25 uses the IMBE (Improved MultiBand
  Excitation) Vocoder convert from Analog to
  Digital.
• The Transmitter encodes analog information to
  digital.
• The Receiver decodes digital information back to
  analog.
• 88 bits of data represent 20 ms of speech.
• The Vocoder encodes all aspects of speech such as
  tone, and audio level into a digital stream of
  bits.
• Digital Information is transmitted using C4FM
  modulation format for Project 25 Phase 1
• The Raised Cosine Nyquist Filter is used as a
  shaping filter to prevent co-channel interference

7
Analog FM Modulation

• With Analog FM, the carrier is moved in frequency
  with respect to the modulating source.
• The signal viewed on the spectrum analyzer is
  constantly changing in occupied bandwidth.

8
C4FM Digital Modulation

• With Digital C4FM, the carrier is moved to
  specific frequency offsets regardless of the
  modulating source.
• The signal viewed on the spectrum analyzer is
  constant in occupied bandwidth.

4800 Symbols
IMBEvocoder
4400 bps Voice information
Nyquist Filter
9600 bps
2400 bps Signaling2800 bps Error Correction
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P25 Modulation (9600 Baud / 4800 Symbols)

• C4FM Modulation for Project 25 Phase I
• 4 Level FSK (Phase Only)
• Information Symbol Deviation
• 01 3 1.8kHz
• 00 1 0.6kHz
• 10 - 1 - 0.6kHz
• 11 - 3 - 1.8kHz
• CQPSK Modulation for Project 25 Phase II
• Compatible Differential Quadrature Phase Shift
  Keying (Phase and Amplitude)
• Information Symbol Phase change
• 01 3 1350
• 00 1 450
• 10 - 1 - 450
• 11 - 3 - 1350

10
P25 - Logical Message Structure
The Header is not encrypted
Link Control
Low Speed Data
Encryption
2
3
4
5
6
7
8
9
1
IMBE Frame 20 msec w/ 88 bits of info 56
bits parity check (4.4bps)
180 msec
LDU2
Logical Link Data Unit (LDU)LDU1
Header - 648 bits w/ 120 bits of info
containing- Message Indicator (Encryption
Algorithm)- Manufacturers ID- Algorithm ID-
Key ID- Talkgroup ID
Link Control (LC) - 240 bits w/ 72 bits of info
containing- Talkgroup ID- Source ID-
Destination ID- Emergency Indicator-
Manufacturer ID
Encryption - 240 bits w/ 96 bits of info
containing- Message Indicator- Algorithm ID for
encryption- Key ID for encryption key
Low Speed Data - 89.2bps currently not in use-
possible application would be transmission of
accurate geographic location information
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How does Digital P25 Impact Testing Requirements

• Power
• Frequency
• Analog Modulation Accuracy
• Digital C4FM Modulation Accuracy
• P25 Test Signals
• Analog Receiver Sensitivity
• Digital P25 Receiver Sensitivity
• Protocol Testing
• Harmonics

12
Power Measurements

• Power measurements for Digital C4FM can be made
  with a standard peak detecting power meter the
  same as with analog FM.
• C4FM digital transmissions are of constant
  amplitude.
• Power measurements for Digital CQPSK cannot be
  made with a standard power meter. The signal
  must be decoded through Digital Signal Processing
  and calculated.

13
Frequency measurements for Digital modulation

• C4FM Frequency measurements can be made with a
  standard frequency counter but may appear to be
  unstable unless the radio is configured to
  transmit a LOW DEVIATION PATTERN as described
  in the ANSI/TIA/EIA-102CAAA standard.
• CQPSK frequency measurements must be made through
  Digital Signal Processing where the signal is
  decoded and the frequency is calculated. A
  standard frequency counter is not usable for this
  type of signal.

14
Measuring Analog Modulation Accuracy

• A deviation meter is used to measure analog FM
  Modulation Accuracy.
• The deviation meter monitors peak carrier
  movement above and below the carrier center
  frequency and displays the average offset.
• Various IF Bandwidth filters are required to
  ensure accurate measurements.

15
Selecting an appropriate IF Bandwidth

• With a Spectrum Analyzer measure the bandwidth of
  the modulated signal 26 dB down from the signal
  peak and add 20.
• The test receivers IF bandwidth should be at
  least this wide.
• IF BW too narrow causes distortion or
  compression.
• IF BW too wide allows excessive noise.
• With constant rate use Carsons Rule
• 2 (Rate Deviation)

-26 dBc
Required BW 20
16
Measuring P25 C4FM Modulation Accuracy

• Testing modulation accuracy of a P25 digital
  signal can be done with two methods.
• Deviation Meter Method
• Measurements can be made with a deviation meter
  if the radio is configured to a defined test
  pattern where the radio is transmitting all high
  or all low bits.
• Problems arise because a deviation meter measures
  only peak deviation and the measurement is not
  synchronized with the symbols.

17
Measuring P25 C4FM Modulation Accuracy

• A Sampling Method takes deviation measurements at
  specific time intervals.
• Measurements are taken synchronously with the
  decoded symbol clock.
• Measurements are averaged over a group of symbols
  and a percentage of error is calculated.
• The measured deviation is only important at
  symbol time.
• The sampling method requires no special setups.

1.8
0.6
-0.6
-1.8
18
Analog Receiver Sensitivity

• Receiver sensitivity in Analog systems is a
  measure of the amount of RF signal level that is
  required to produce an intelligible audio when
  demodulated.
• The measurement device used in analog systems is
  typically the SINAD meter which shows a ratio in
  dB of
• Signal Noise Distortion
• Noise Distortion.

19
P25 Digital Receiver Sensitivity

• The term used to quantify a digital receivers
  performance is BER (Bit Error Rate).
• The test must be conducted with a known test
  signal such as the 1011 pattern.
• Radio specific software and a computer may be
  required to evaluate a decoded 1011 tone. The
  radio is placed into a special test mode for this
  test.
• Another method is to listen to the decoded audio.
• A digital signal will stop decoding abruptly when
  the BER becomes high.

The IFR 2975 provides a SPEECH encoder with
defined messages to test the vocoder at any TGID,
SID or NAC configuration.
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Testing Protocol (CAI)

• Protocol testing requires the ability to decode
  the 9600 baud data into voice and data
  information.
• After decoding, the data bits are reconstructed
  into their original message elements.
• Decoding allows quick verification of the radio
  programming.
• Allows testing of EMERGENCY facility off the air.
• Decoding can also be used to evaluate Transmit
  BER.

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IFR-2975 Overview

• 2975

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Powerful Processing Features

• Pentium Processor
• Internal Storage
• Hard Drive
• 3.5 Floppy
• Display
• Color LCD
• Sunlight Readable
• Portable Rugged Design
• All Digital System (DSP)
• Field Upgradeable

33 lbs.
23
Rear Panel I/O

• Ethernet (10T/100T)
• 2 USB ports
• Printer port
• RS-232
• GPIB
• VGA Output
• Keyboard input
• Mouse port
• Universal Power Supply
• 110/220 operation

24
Remote Access

• X-Windows operating under VX Works
• IP Addressable
• Network Accessible
• Route Display and Keyboard to a remote computer
• TCL / TK scripting language support

25
Legacy Support

• Power Meter (Wide and Narrow band)
• Deviation, Distortion, SINAD
• RF and Audio Counters
• Digital AC/DC Voltmeter
• Quad Function Generators
• FM Modulation
• 600 Ohm Balanced / Unbalanced Audio Input / Output

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Extended Features

• 2.7 GHz frequency coverage (1 Hz resolution)
• Generate (10 to -137 dBm Output level)
• Receive (Protected Input)
• Crossband Duplex (Encode / Decode Simultaneously)
• Signal Tracing
• High Stability Reference Oscillator 0.01 PPM
• High Resolution Spectrum Analyzer
• 10 dBm Tracking Generator
• Dual Input Digital Storage Scope

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Project 25 Unique Features

• C4FM Modulation Analyzer
• DES OFB Type III
• Encryption / Decryption
• IMBE Vocoder (Encode / Decode)
• Embedded Voice Speech patterns
• Allows receiver testing without special test
  modes.
• C4FM Modulation Source
• Common Air Interface Testing
• Decode Uplink Data
• Encode Downlink Data

28
Flexible Operator Interface

• The operator interface allows the flexibility to
  choose what meters are available on each screen
• Both the Spectrum and Scope can be viewed
  simultaneously

29
IFR-2975 Functional Test Screens

• Basic Operation
• Generate (RX Test)
• Receive (TX Test)
• Duplex
• Function Generator
• Scope
• Spectrum Analyzer
• Project 25 Repeater Simulator
• System Configuration

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Functional Test Screen Selections

• Operational Mode selections are made by pressing
  the MODE key to access a pull down selection
  menu.
• OR position the cursor to the Function Selector
  and press the ENTER key.
• OR mouse click on the Function Selector.
• Enter a menu item number or use data scroll
  features and the ENTER key.

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Selecting Function Options

• Function Option selections are made by pressing
  the SHIFT MODE keys to access a pull down
  selection menu.
• OR position the cursor to the Function Option
  Selector and press the ENTER key.
• OR mouse click on the Function Option Selector.
• Enter a menu item number, use data scroll
  features and the ENTER key.

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Generate (RX Test)

• Signal Generator
• FM / C4FM (P25)
• Receiver Stimulus
• Dual Modulation sources
• Distortion / SINAD meter
• Scope
• DVM

33
Receiver Tests
34
Receive (TX Test)

• Off Air Monitor
• Transmitter Test
• Power Meter
• 50 W Cont.
• 125 W 1 on / 4 off
• Deviation Meter
• Distortion Meter
• Scope
• DVM
• FM / C4FM (P25)

35
Transmitter Tests
36
Duplex (RX / TX Test)

• Simultaneous Generate and Receive operation.
• Cross-band Repeater testing
• Signal Tracing
• All in one radio test screen
• FM / C4FM (P25)

37
Function Generator

• Base-band Audio Tests
• Dual Function Generators
• DVM
• AF Counter
• Distortion Meter
• SINAD Meter
• Balanced / Unbalanced

38
Scope

• Dual channel Ext. Input
• Monitor Audio In
• Monitor MIC

39
Spectrum Analyzer

• Full Span 2.7 GHz
• Independent controls
• Video Filters
• Tracking Generator

40
Cable Fault measurement

• The Tracking Generator level may be adjusted to
  place the dips closely to the center horizontal
  line to allow use of the grid markings.
• The Center Frequency may be adjusted to position
  one of the dips closely to a vertical grid line.

41
P25 Repeater Simulator

• Encode UPLINK data
• Decode DOWNLINK data
• Receiver test patterns
• Transmitter Modulation Accuracy test.

42
System Configuration

• Configure IP address
• Redirect 2975 operations to a network computer.
• RS-232 settings
• GPIB address
• Internal / External Reference.

43
Bessel Null Measurements
Modulation Index for a 1 kHz Rate
Rate Desired Dev (Hz) / Mod Index 3300 Hz Dev /
2.405 1372.1 Hz for Carrier Null (52 dB)
44
Generate Scope
45
Receive Scope
46
Receive Analyzer
47
Receive Audio Routing
AC25007
48
Power Meter
49
Deviation Meter
50
Generate Audio Routing
AC25007
51
Duplex Audio Routing
AC25007
52
Distortion Meter
53
SINAD Meter
54
DVM
55
C4FM Meter
56
RF Error Meter
57
AF Counter
58
Alternate configuration for Receive Screen
59
IF Bandwidth Filters

• 12.5 kHz

• 25 kHz

• 200 kHz

60
C4FM Modulation Analyzer

• The Deviation level of each symbol is measured
  and the average error is displayed
• Allows modulator accuracy testing without special
  test modes.

01
10
00
11
1.8
-1.8
-0.6
0.6
C4FM Deviation
61
Common Air Interface (Uplink Data)

• Project 25 Uplink data can be decoded and
  displayed
• Verify radio Programming
• Verify Emergency mode without disturbing the
  system
• Monitor for TX BER

62
Common Air Interface (Downlink)

• P25 Downlink information can be specified and
  Encoded
• Verify new radio software loads prior to allowing
  onto the system
• Test unusual situations to verify the radio
  responds correctly

63
P25 Test Signals

• Some common Test Signals have been defined for
  P25 measurements.
• Test Signals have been defined with a TGID of 1,
  SID of 1, and a NAC of 293.
• 1011
• When decoded, the 1011 pattern sounds like the
  traditional 1 kHz tone used to test analog
  systems.
• Calibration
• When decoded, the Calibration pattern sounds like
  an unstable 1 kHz tone. The Calibration pattern
  is a 1011 tone with a 5 Bit Error added.
• SILENCE
• When decoded, there should be no sound from the
  P25 receiver.

The IFR 2975 provides a SPEECH encoder with
defined messages to test the vocoder at any TGID,
SID or NAC configuration.