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Digital Communication How it started, what it is & we can do with it today!

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Presentation on theme: "Digital Communication How it started, what it is & we can do with it today!"— Presentation transcript:

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2 Digital Communication How it started, what it is & we can do with it today!

3 How It Started 1831 Insulated Wire 1831 Insulated Wire 1836 Morse Code 1836 Morse Code 1843 Fascimile 1843 Fascimile 1870 Baudot Code 1870 Baudot Code

4 Wires & Solenoids Current Loop Systems Current Loop Systems Ranges in Miles Ranges in Miles Easy Repeaters Easy Repeaters Multiple Stations Multiple Stations

5 Morse Code 1836 International Morse code composed of five elements: International Morse code composed of five elements: 1. short mark, dot - "dot duration" is one unit long 1. short mark, dot - "dot duration" is one unit long 2. longer mark, dash is three units long 2. longer mark, dash is three units long 3. inter-element gap within a character one unit long 3. inter-element gap within a character one unit long 4. short gap (between letters) three units long 4. short gap (between letters) three units long 5. medium gap (between words) seven units long 5. medium gap (between words) seven units long Only non time sensitive digital scheme Only non time sensitive digital scheme

6 Morse Code 1836 Manual Send, Paper Tape Receive Manual Send, Paper Tape Receive First was soft paper & pin to crease tape First was soft paper & pin to crease tape Operators learn to hear the code, tape is abandoned Operators learn to hear the code, tape is abandoned (If you understand click and clack) (If you understand click and clack)

7 Morse Code 1836

8 Fax Machine 1843 Write message in non-conductive ink on metal plate Write message in non-conductive ink on metal plate Scan sheet with a needle Scan sheet with a needle Remote solenoid makes inverse image Remote solenoid makes inverse image Requires synchronized clockworks Requires synchronized clockworks

9 Baudot Code 5 Element byte, two hand keyboard 5 Element byte, two hand keyboard 2 & 3 Fingers, 30 WPM 2 & 3 Fingers, 30 WPM

10 Baudot Code Manual or punched tape on send Manual or punched tape on send Used punched paper tape on receive Used punched paper tape on receive Sender clockworks switches current Sender clockworks switches current Receiver steps tape, activates 5 solenoids Receiver steps tape, activates 5 solenoids 5 bits means 32 symbols (letters) 5 bits means 32 symbols (letters) Still used by TDD phone devices Still used by TDD phone devices Still used by hams today for RTTY Still used by hams today for RTTY

11 Baudot Code Shift codes select alternate meanings Shift codes select alternate meanings

12 Digital Radio Modes There are 10 kinds of people in the world - those who understand binary and those who dont. There are 10 kinds of people in the world - those who understand binary and those who dont FCC allows ASCII for hams 1980 FCC allows ASCII for hams PCs and sound cards make it practical PCs and sound cards make it practical Hams invent new modes – endlessly! Hams invent new modes – endlessly! JT-9 Announced last November – for 160M JT-9 Announced last November – for 160M

13 What is ASCII? American Standard Code for Information Interchange American Standard Code for Information Interchange Originally a 7 bit code Originally a 7 bit code Later 6 bit (half ascii) and 8 bit (extended) Later 6 bit (half ascii) and 8 bit (extended) 6 bits means 64 values (no lower case) 6 bits means 64 values (no lower case) 7 bits means 128 values 7 bits means 128 values 8 bits allows 256 values 8 bits allows 256 values Shift In, Shift Out, Escape extends further (DEC screen positioning codes) Shift In, Shift Out, Escape extends further (DEC screen positioning codes)

14 Whats a Byte? 0 or 1, hi or low, 1270 / 1070 Hz, ??? 0 or 1, hi or low, 1270 / 1070 Hz, ??? 1 start bit 1 start bit 6,7,or 8 data bits 6,7,or 8 data bits 1 parity bit (Odd, even, or none) 1 parity bit (Odd, even, or none) 1 stop bit 1 stop bit Allows unsynchronized clocks Allows unsynchronized clocks Allows simple error checking Allows simple error checking

15 Why All These Modes? Radio is an analog medium Radio is an analog medium Propagation is variable Propagation is variable Bandwidth is limited Bandwidth is limited Speed vs reliability Speed vs reliability Because we can! Because we can!

16 Basic Principles Input data in binary form used to modulate Input data in binary form used to modulate Can change amplitude, frequency, phase Can change amplitude, frequency, phase Can use multiple tones Can use multiple tones Mathematical functions used to generate an analog signal Mathematical functions used to generate an analog signal Same math functions used to recover data from analog signal Same math functions used to recover data from analog signal Can include compression and error recovery Can include compression and error recovery Everyone can invent a better function! Everyone can invent a better function!

17 The Big Modes – RTTY 1922 Usually 45 Baud, 170 Hz Signal, some 75 baud Usually 45 Baud, 170 Hz Signal, some 75 baud At 45 baud about 60 words per minute At 45 baud about 60 words per minute Surplus Teletype Model 26 in 1946 Surplus Teletype Model 26 in 1946 FSK / AFSK audio frequency shift keying FSK / AFSK audio frequency shift keying PCs now function as glass teletype PCs now function as glass teletype Popular contest mode Popular contest mode

18 The Big Modes – The TORs SITOR - Simplex Telex Over Radio SITOR - Simplex Telex Over Radio AMTOR – Amateur SITOR (1970) 100 baud AMTOR – Amateur SITOR (1970) 100 baud PACTOR – AMTOR / Packet combo 200 baud PACTOR – AMTOR / Packet combo 200 baud Data is sent in groups of 3 characters Data is sent in groups of 3 characters Receiver responds to each 3 character group ACK/NAK Receiver responds to each 3 character group ACK/NAK NAK causes retransmission of group NAK causes retransmission of group Implies two station comms only Implies two station comms only

19 The Big Modes – Packet 1200 bps AFSK TNCs used on 2-meters 1200 bps AFSK TNCs used on 2-meters AX.25 Protocol specifies channel access (ability to transmit on the channel) to be handled by CSMA (Carrier Sense Multiple Access). AX.25 Protocol specifies channel access (ability to transmit on the channel) to be handled by CSMA (Carrier Sense Multiple Access). Digipeaters retransmit if its call is in the digipeater field Digipeaters retransmit if its call is in the digipeater field APRS is a packet system APRS is a packet system

20 The Big Modes – PSK31 Developed by Peter Martinez G3PLX in 1995 Developed by Peter Martinez G3PLX in 1995 Uses phase shift keying (BPSK or QPSK) Uses phase shift keying (BPSK or QPSK) Throughput is 31 baud, bandwidth is 31Hz Throughput is 31 baud, bandwidth is 31Hz CW transmitter must put out 15 to 18 times more power than a PSK31 transmitter, to achieve the same S/N ratio at the Rx CW transmitter must put out 15 to 18 times more power than a PSK31 transmitter, to achieve the same S/N ratio at the Rx PSK31 more susceptible to frequency changes than CW or RTTY but b etter under weak signal conditions PSK31 more susceptible to frequency changes than CW or RTTY but b etter under weak signal conditions

21 The Big Modes – MT63 MT63 distributes the encoding of each character over a long time period, and over several tones. 100 WPM MT63 distributes the encoding of each character over a long time period, and over several tones. 100 WPM 64 tones Hz apart, in a 1kHz bandwidth 64 tones Hz apart, in a 1kHz bandwidth Even if 25% of the character sent is obliterated, it will give perfect copy Even if 25% of the character sent is obliterated, it will give perfect copy Wide bandwidth (1Khz for the standard method) makes this mode less desirable on crowded ham bands such as 20 meters Wide bandwidth (1Khz for the standard method) makes this mode less desirable on crowded ham bands such as 20 meters

22 Some lesser modes - Clover PSK mode which provides a full duplex simulation PSK mode which provides a full duplex simulation Suited for HF operation (especially under good conditions) Suited for HF operation (especially under good conditions) Clovers key characteristics are band-width efficiency with high error-corrected data rates Clovers key characteristics are band-width efficiency with high error-corrected data rates Clover adapts to conditions by constantly monitoring the received signal Clover adapts to conditions by constantly monitoring the received signal Hardware based mode and limited use Hardware based mode and limited use

23 Some lesser modes - Hellschreiber A method of sending and receiving text using facsimile technology A method of sending and receiving text using facsimile technology This mode has been around a long time; the recent use of PC sound cards as DSP units has increased the interest in Hellschreiber This mode has been around a long time; the recent use of PC sound cards as DSP units has increased the interest in Hellschreiber The single-tone version (Feld-Hell) is the method of choice for HF operation The single-tone version (Feld-Hell) is the method of choice for HF operation 35 WPM text rate, with a narrow bandwidth (about 75 Hz). 35 WPM text rate, with a narrow bandwidth (about 75 Hz). Text characters are "painted" on the screen, as apposed to being decoded and printed Text characters are "painted" on the screen, as apposed to being decoded and printed As a "fuzzy mode" it has the advantage of using the "human processor" for error correction. As a "fuzzy mode" it has the advantage of using the "human processor" for error correction.

24 Some lesser modes – MFSK-16 An advancement to the THROB mode and encodes 16 tones An advancement to the THROB mode and encodes 16 tones Uses Fast Fourier Transform technology to decode the ASCII characters, and Constant Phase Frequency Shift Keying to send the coded signal. Uses Fast Fourier Transform technology to decode the ASCII characters, and Constant Phase Frequency Shift Keying to send the coded signal. Continuous Forward Error Correction (FEC) sends all data twice with an interleaving technique to reduce errors from impulse noise and static crashes Continuous Forward Error Correction (FEC) sends all data twice with an interleaving technique to reduce errors from impulse noise and static crashes The relatively wide bandwidth (316 Hz) for this mode allows faster baud rates (typing is about 42 WPM) and greater immunity to multi path phase shift The relatively wide bandwidth (316 Hz) for this mode allows faster baud rates (typing is about 42 WPM) and greater immunity to multi path phase shift Becoming a standard for reliable keyboard to keyboard operation and is available in several popular programs Becoming a standard for reliable keyboard to keyboard operation and is available in several popular programs

25 Some lesser modes – WSPR For sending and receiving low-power transmissions to test propagation paths on the MF and HF bands For sending and receiving low-power transmissions to test propagation paths on the MF and HF bands Can decode signals with S/N as low as -28 dB in a 2500 Hz bandwidth Can decode signals with S/N as low as -28 dB in a 2500 Hz bandwidth Standard message: callsign + 4-digit locator + dBm (i.e. K1ABC FN20 37) Standard message: callsign + 4-digit locator + dBm (i.e. K1ABC FN20 37) Duration of transmission: seconds Duration of transmission: seconds Transmissions nominally start one second into an even UTC minute: i.e., at hh:00:01 Transmissions nominally start one second into an even UTC minute: i.e., at hh:00:01

26 NBEMS Narrow Band Emergency Messaging System Consists of four programs: Fldigi – Fast Light Digital modem application Flarq – Fast Light Automatic Repeat Request Flwrap – embed a checksum in a file Flmsg – easily send ICS forms and Radiogram

27 NBEMS philosophy Keep it cheap. Keep it simple. Use Open Source software. Don't depend upon infrastructure. Make it fun to use between drills and disasters. Any computer, any radio.

28 How NBEMS Works Fldigi uses your computer's sound card to generate and decode digital signals. All work is done by your computer, don't need an external Terminal Node Controller (TNC). Audio from your computer speakers go into your radio's mike input for transmission. Audio from your radio goes into your computer's mike or line-in for decoding. Don't need an extremely powerful new computer, older machines work just fine.

29 Interfacing with computer Rigblaster SignaLink But, if necessary, hold radio mike up to computer speaker and... Hold radio speaker up to computer mike! In an emergency, don't really need hardwired interface. Disable all DSP enhancement programs on mic

30 Acoustic Interface Easiest way to interface radio to computer is to... Hold radio mike up to computer speakers. Hold radio speaker up to computer mike. You do PTT manually. Works especially well with VHF/UHF FM. Real gamesaver during emergencies. Allows you to easily send data using any radio. Hams can participate who do not have a soundcard interface. MT63 is sufficiently robust to deal with background noise, even in a noisy EOC or field site.

31 Signalink USB

32 SignaLink Configuration SignaLink is very easy to configure. Just connect to computer via USB. Configure Fldigi to use SignaLink USB sound card. Generate just enough audio from computer to trigger SignaLink vox. Use volume controls on SignaLink and don't touch computer audio settings

33 What Modes ? Operating Mode Operating Mode MT63 – 2000 MT63 – 2000 Olivia 16/500 Olivia 16/500 If you have a decent FM voice channel start with MT If you have a decent FM voice channel start with MT When MT fails, switch to Olivia 16/500 When MT fails, switch to Olivia 16/500 When Olivia fails, no communications. When Olivia fails, no communications.

34 ARRL Radiogram Calculate Check Today Pick ARRL Message

35 ARRL Radiogram Delivery

36 ICS 213 Form

37 IC 213 HTML Delivery

38 Where to find digital modes?? 6 Meter Band: Mhz 6 Meter Band: Mhz 10 Meter Band: Mhz 10 Meter Band: Mhz 12 Meter Band: Mhz 12 Meter Band: Mhz 15 Meter Band: Mhz 15 Meter Band: Mhz 17 Meter Band: Mhz 17 Meter Band: Mhz 20 Meter Band: Mhz 20 Meter Band: Mhz 30 Meter Band: Mhz 30 Meter Band: Mhz 40 Meter Band: Mhz 40 Meter Band: Mhz 80 Meter Band: & Mhz 80 Meter Band: & Mhz

39 And What About D-Star? All digital, all the time All digital, all the time Combined voice & data in 20 ms chunks Combined voice & data in 20 ms chunks Data stream about ½ voice, ½ data Data stream about ½ voice, ½ data Voice input is digitized, compressed, merged with data – calllsigns, repeater, routing, text Voice input is digitized, compressed, merged with data – calllsigns, repeater, routing, text GMSK modulation to create analog signal– like cell phones GMSK modulation to create analog signal– like cell phones Limited forward error correction Limited forward error correction

40 What does D-Star Add? Call Routing – repeater to repeater Call Routing – repeater to repeater Reflectors – Hub for repeater spokes Reflectors – Hub for repeater spokes Allows simple text & small file exchange Allows simple text & small file exchange Now HF as well as VHF / UHF Now HF as well as VHF / UHF

41 What Next? Club event to set up PCs and radios Club event to set up PCs and radios NBEMS net on W1SYE NBEMS net on W1SYE Perhaps start a Digital Team of Elmers Perhaps start a Digital Team of Elmers Could we build a Rhode Island Net? Could we build a Rhode Island Net?


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