Test Slide

Complex Data Modes for Beginners Mike Richards G4WNC

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

Complex Modes - Modulation MFSK simple 8-tone example f8 f7 f6 f5 f4 f3 f2 f1 Time Olivia 32/1000 ROS 16/2000 12th Sept 2012 Mike Richards - Introduction to Data Modes (RSGB 2012)

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)

Complex Modes – Modulation - Interleaving 4 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)

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)

Complex Modes – Mode Summary Bandwidth Keying Error Correction Mode ARQ/FEC FEC Coding Purpose AMTOR 170 FSK ARQ QSO PACTOR 200Hz HF email 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)

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)

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)

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)

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)