Presentation is loading. Please wait.

Presentation is loading. Please wait.

Test Slide Complex Data Modes for Beginners Mike Richards G4WNC.

Similar presentations


Presentation on theme: "Test Slide Complex Data Modes for Beginners Mike Richards G4WNC."— Presentation transcript:

1

2 Test Slide

3 Complex Data Modes for Beginners Mike Richards G4WNC

4 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) 3

5 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) 4

6 Complex Modes - Overview 12th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 5

7 Data Modes – Data Preparation 12th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 6

8 A UNICODE(ASCII) 65 Keyboard Serial data Keyboard to Serial Data 6th Sept Mike Richards - Complex Modes (RSGB 2012)

9 Complex Modes – Channel Coding 6th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 8 Encoding

10 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) 9

11 Dealing with errors – 1: Speech Signals 6th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 10 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

12 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) 11

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

14 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) 13

15 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) 14

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

17 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) 16

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

19 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 12th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 18 Flip-flop

20 Channel Coding – Convolutional Coding Summary 6th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 19 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

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

22 Complex Modes – Modulation Systems 6th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 21 Encoding

23 Complex Modes - Modulation We have a protected data stream What else can we do to ensure safe transit? Decoding systems dont like high levels of consecutive bit errors Spread data in both frequency and time 12th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 22

24 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) 23

25 Complex Modes - Modulation Frequency spreading example – Olivia uses 32 tones in a 1000Hz bandwidth – 32 tone combinations = 0-31 in binary = 12th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) = 5-bits per tone (Symbol)

26 Complex Modes - Modulation 12th Sept 2012 Mike Richards - Introduction to Data Modes (RSGB 2012) 25 – MFSK simple 8-tone example Time f1 f2 f3 f4 f5 f6 f7 f8 Olivia 32/1000 ROS 16/2000

27 Complex Modes - Modulation Time Spreading – Avoid consecutive bit damage – Minimises damage from impulse noise Heres an example: 12th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 26

28 Complex Modes – Modulation - Interleaving 12th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 27 ABCDEF GHIJK MO L NPQR STUVWX YZ YSMGA Input by row Output by column

29 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) 28

30 Complex Modes – Mode Summary ModeBandwidthKeying Error Correction Mode ARQ/FEC FEC CodingPurpose AMTOR 170 FSK ARQ QSO PACTOR 200Hz FSK ARQ HF QPSK31 31Hz QPSK FECConvolutionalQSO MFSK16 360Hz MFSK FECNASAQSO JT65A 200Hz MFSK FEC Reed- Solomonspecialist weak signal ALE 1750Hz MFSK FECGOLAYLink control ROS 500 or 2000Hz MFSK FECNASAQSO/ weak signal WINMOR 500 or 1600Hz MFSK bothNASAHF V4Chat 200Hz MFSK bothNASAQSO Olivia 125 to 2000Hz MFSK FECWalshQSO/weak signal MT to 2000Hz MPSK FECWalshQSO/weak signal 12th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 29

31 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) 30

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

33 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) 32

34 Questions Have a go – its fun Any Questions? Dont forget to pick-up a handout 6th Sept 2012 Mike Richards - Complex Modes (RSGB 2012) 33


Download ppt "Test Slide Complex Data Modes for Beginners Mike Richards G4WNC."

Similar presentations


Ads by Google