1. Test Slide

2. Complex Data Modes for Beginners
Mike Richards G4WNC

3. Mike Richards – Complex Data Modes
The Menu for Today
Complex Data Modes – What & Why?
Process Flow Chart
Technical bits.
What You Need
Operating
Summary & Questions
6th Sept 2012
Mike Richards – Complex Data Modes
(RSGB 2012)

4. Complex Modes – What & Why?
What are complex modes?
Digital communication systems that have been designed to be more reliably than simple modes
Why bother?
Self Education
A new dimension to your radio operating
Facilitates operating under poor conditions
Great for QRP and DX
You can do it for free!
6th Sept 2012
Mike Richards - Complex Modes (RSGB 2012)

5. Complex Modes - Overview
Alphabet
Conversion
Data
Preparation
Channel
Coding
Modulation R A D I O L N K
Recovery
De-modulation
Encoding
Decoding
12th Sept 2012
Mike Richards - Complex Modes (RSGB 2012)

6. Data Modes – Data Preparation
Alphabet
Conversion
Data
Preparation
Channel
Coding
Modulation R A D I O L N K
Recovery
De-modulation
Encoding
Decoding
12th Sept 2012
Mike Richards - Complex Modes
(RSGB 2012)

7. Keyboard to Serial Data
UNICODE(ASCII) 65 1
128 64 32 16 8 4 2
Serial
data 1 1
6th Sept 2012
Mike Richards - Complex Modes
(RSGB 2012)

8. Complex Modes – Channel Coding
Alphabet
Conversion
Data
Preparation
Channel
Coding
Modulation R A D I O L N K
Recovery
De-modulation
Encoding
Decoding
Encoding
6th Sept 2012
Mike Richards - Complex Modes
(RSGB 2012)

9. Mike Richards - Complex Modes
Channel Coding -1
Adapt the message to suit the link
Add error detection and or protection
Two link categories
1:1 link supporting duplex operation
Real time communications in both directions
Supports Automatic Repeat Request (ARQ)
Broadcast
Unidirectional link
Requires Forward Error Correction (FEC)
6th Sept 2012
Mike Richards - Complex Modes
(RSGB 2012)

10. Dealing with errors – 1: Speech Signals
Ignore
Rely on distant operator to work-out errors
Repeat
Say everything twice
Short messages and confirm
Word at a time and confirm receipt
Use phonetics
Add more information to get through
6th Sept 2012
Mike Richards - Complex Modes
(RSGB 2012)

11. Dealing with errors – 2: Data Modes
In data modes we use:
Automatic Repeat Request (ARQ)
Send short data bursts and await confirmation
Forward Error Correction (FEC)
Add extra information to enable the receive station to recover a damaged message
6th Sept 2012
Mike Richards - Complex Modes
(RSGB 2012)

12. Channel Coding - Automatic Repeat Request (ARQ)
Send data in short bursts
Wait for acknowledgement
Repeat on request
Originator
Data 1
Data 2
Data 2
Data 3
Distant Stn
ACK
ARQ
ACK
ACK
6th Sept 2012
Mike Richards - Complex Modes
(RSGB 2012)

13. Mike Richards - Complex Modes
Channel Coding – ARQ
Pros:
Can be very reliable and great for QRP
Excellent with deep QSB
Type everything once – system handles the repeats
Used by Winmor, V4Chat, Amtor, Pactor, Packet
Cons:
Often slow
Protracted repeats under poor conditions
Only caters for 1:1 connections
12th Sept 2012
Mike Richards - Complex Modes
(RSGB 2012)

14. Mike Richards - Complex Modes
Channel Coding - FEC
FEC
Most commonly used form of error correction
Adds information to the message
Phonetics for digital
Known as redundancy
Very powerful
NASA use these techniques to recover data from space probes 11 billion miles away!
12th Sept 2012
Mike Richards - Complex Modes
(RSGB 2012)

15. Channel Coding – Simple FEC
Simple Forward Error Correction
Original text H E L O
Repeated text H E L O
Transmitted text H ~ E L O
~ = Data padding
Used for AMTOR FEC and NAVTEX marine safety system
6th Sept 2012
Mike Richards - Complex Modes
(RSGB 2012)

16. Mike Richards - Complex Modes
Channel Coding - FEC
Simple FEC very limited
Require a more sophisticated solution
NASA Voyager space program
Developed a system using convolutional coding
Very powerful
Produces an output that is the result of processing the 7-bits currently in the coder
12th Sept 2012
Mike Richards - Complex Modes
(RSGB 2012)

17. Channel Coding – FEC Convolutional Coding
Uses flip-flops or shift registers
Each clock pulse moves the input data to the output 1 1 1 1 1 1 1
Clock pulse
7-bits contained within the coder = constraint
12th Sept 2012
Mike Richards - Complex Modes
(RSGB 2012)

18. Channel Coding – Convolutional Coding
Extract two outputs from the coder
Each bit entering produces 2-bits out = Rate
Simple model with constraint 3 and rate 1/2 1 01 1 11 00 00 1 11
Flip-flop
Flip-flop
12th Sept 2012
Mike Richards - Complex Modes
(RSGB 2012)

19. Channel Coding – Convolutional Coding Summary
Creates a pattern from all the bits within the coder
Defined by Constraint (k) and Rate (Input bits/Output bits)
NASA Voyager algorithm most common
K = 7 rate = ½
Used in MFSK16, ROS, WINMOR, V4Chat, QPSK31, JT65A
6th Sept 2012
Mike Richards - Complex Modes (RSGB 2012)

20. Channel Coding – Walsh functions
Alternative coding system
Used in Olivia and MT63
Each 7-bit ASCII character produces a 64-bit output
12th Sept 2012
Mike Richards - Complex Modes (RSGB 2012)

21. Complex Modes – Modulation Systems
Alphabet
Conversion
Data
Preparation
Channel
Coding
Modulation R A D I O L N K
Recovery
De-modulation
Encoding
Decoding
Encoding
6th Sept 2012
Mike Richards - Complex Modes (RSGB 2012)

22. Complex Modes - Modulation
We have a protected data stream
What else can we do to ensure safe transit?
Decoding systems don’t like high levels of consecutive bit errors
Spread data in both frequency and time
12th Sept 2012
Mike Richards - Complex Modes (RSGB 2012)

23. Complex Modes - Modulation
Frequency Spreading
Most modes do this
Employs multiple tones
Bandwidth up to 2kHz
Contentious?
12th Sept 2012
Mike Richards - Complex Modes
(RSGB 2012)

24. Complex Modes - Modulation
Frequency spreading example
Olivia uses 32 tones in a 1000Hz bandwidth
32 tone combinations = 0-31 in binary = 1 4 2 8 16
= 5-bits per tone (Symbol)
12th Sept 2012
Mike Richards - Complex Modes
(RSGB 2012)

25. Complex Modes - Modulation
MFSK simple 8-tone example f8 f7 f6 f5 f4 f3 f2 f1
Time
Olivia 32/ ROS 16/2000
12th Sept 2012
Mike Richards - Introduction to Data Modes (RSGB 2012)

26. Complex Modes - Modulation
Time Spreading
Avoid consecutive bit damage
Minimises damage from impulse noise
Here’s an example:
12th Sept 2012
Mike Richards - Complex Modes
(RSGB 2012)

27. Complex Modes – Modulation - Interleaving4 Y S M G A A B C D E F G H I J K L
Input by row
Output by column M N O P Q R S T U V W X Y Z 1 2 3 4 5 6 7 8 9
12th Sept 2012
Mike Richards - Complex Modes
(RSGB 2012)

28. Complex Modes – Coding & Modulation Summary
Two key points
We add extra information (redundancy) to facilitate error correction
We disperse the signal in time and frequency to minimise errors.
12th Sept 2012
Mike Richards - Complex Modes (RSGB 2012)

29. Complex Modes – Mode Summary
Bandwidth
Keying
Error
Correction Mode
ARQ/FEC
FEC Coding
Purpose
AMTOR
170
FSK
ARQ
QSO
PACTOR
200Hz HF
QPSK31
31Hz
QPSK
FEC
Convolutional
MFSK16
360Hz
MFSK
NASA
JT65A
Reed-Solomon
specialist weak signal
ALE
1750Hz
GOLAY
Link control
ROS
500 or 2000Hz
QSO/ weak signal
WINMOR
500 or 1600Hz
both
V4Chat
Olivia
125 to 2000Hz
Walsh
QSO/weak signal
MT63
500 to 2000Hz
MPSK
12th Sept 2012
Mike Richards - Complex Modes (RSGB 2012)

30. Complex Modes Operation – Get Going
What do you need:
PC with a sound card
Windows XP (or later), Linux, Mac
Software – FLDIGI is good
SSB transceiver and Antenna
Two screened leads for audio in and out
Optional interface unit
12th Sept 2012
Mike Richards - Complex Modes
(RSGB 2012)

31. Data Modes – Connections
Line out
Mic in
SSB Transceiver
Computer
Sound Card
Line in
Audio
out
Optional PTT
Line out
Mic in
SSB Transceiver
SignalLink
Interface
USB
Line in
Audio
out
PTT
12th Sept 2012
Mike Richards - Complex Modes
(RSGB 2012)

32. Data Modes – Operating Tips
Listen first
Use Hamspots Digital Section
Use low power – 5 watts is usually plenty
Watch your modulation
Keep to the band plans
Use my sample messages
Try conversing!
12th Sept 2012
Mike Richards - Complex Modes
(RSGB 2012)

33. Mike Richards - Complex Modes
Questions
Have a go – it’s fun
Any Questions?
Don’t forget to pick-up a handout
6th Sept 2012
Mike Richards - Complex Modes
(RSGB 2012)