Why Run HF Digital Modes?

• Smaller bandwidth requirements

– Voice SSB is 2.7 Khz, digital is typically 100hz and up

• May provide longer range for the same power

– Supports forms of error correction

• Possible to decode multiple transmissions at once • Why miss that last QSO or mode award

• Intellectual challenge, it keeps the brain cells working… HF Digital vs VHF/UHF Digital Modes

• Some modes are available on both HF and UHF/VHF (D*Star)

• Radio characteristics – HF requires computer processing and UI elements

– HF antenna is larger, no rubber duckies please �

– Power requirements (not necessarily more than VHF/UHF!)

• Data propagation is different on HF

– Longer distance, ionosphere bounce between stations

– Band characteristics such as higher RF noise, fading Presentation Overview

• Understanding how digital data is sent

• Digital mode practical examples

• Best practice - working split in congested frequencies

• Best practice - using filters to improve performance

• Best practice - propagation and system performance

• System setup for digital operation How Digital Data is Sent

• Modulation is the process of varying a periodic waveform, called the carrier signal, with a modulating signal that typically contains information to be transmitted.

• Error Correction is the process of correcting for damaged or missing information

• A Digital Mode implements modulation over a carrier and possible error correction to send information Understanding Digital Modulation

• Digital modulation falls into three basic categories

– Amplititude Shift Modulation turns a signal on and off on a specific frequency – Frequency Shift Modulation conveys data over multiple frequencies

– Phase Shift Modulation conveys data by shifting the phase of the signal Amplitude Shift Modulation

• Amplitude-shift keying (ASK) conveys data by changing (modulating) the frequency of a reference carrier • The simplest form of ASK operates as a switch, using the presence of a carrier wave to indicate a binary one and its absence to indicate a binary zero. This type of modulation is called on-off keying (OOK), and is used at radio frequencies to transmit Morse code (referred to as continuous wave operation, or CW) Frequency Shift (FSK) Modulation

• Frequency-shift keying (FSK) conveys data by changing (modulating) the frequency of a reference signal

• Binary FSK (BFSK) uses a pair of discrete frequencies to transmit binary (0s and 1s) information.

– With this scheme, the "1" is called the mark frequency and the "0" is called the space frequency.

• Multiple Frequency Shift Keying (MFSK) uses more than 2 frequencies to transmit information Phase Shift (PSK) Modulation, Cont.

• Phase-shift keying (PSK) conveys data by changing (modulating) the phase of a reference signal

• PSK is more spectrum efficient than FSK, since it uses a single carrier frequency

• There are multiple forms of PSK

– BPSK (Binary PSK) utilitzes 2 phases 180 degrees apart

– QPSK (Quadrature PSK) utilizes 4 phases 90 degrees apart

BPSK Modulation QPSK Modulation Error Correction

• Error correction replaces missing or damaged information due to RF noise, interference, and atmospheric issues like signal fading

• (1) Forward Error Correction (FEC) corrects errors by sending some redundant data

– Limited lost data can be recovered without re-transmission

– Complex mathematical models used to predict minimum impact

• (2) Re-transmission of data – Requires a reverse channel to request retransmission of the data

• Error correction improves transmission success, but at the cost of reducing data throughput HF Digital Mode Examples

CW PSK31 RTTY

JT65/JT9 Continous Wave (CW) Morse Code

• CW uses Amplitude Modulation (AMT)

• Bandwidth around 50 Hz • Sent using a ‘key’ or computer generated signal

• Uses a standard code of long and short codes CW (Morse Code) Mode

CW VP8STI (S. Sandwich Islands - #3 Most Wanted PSK31 RTTY

JT65/JT9

CW Skimmer from DXAtlas CW (Morse Code) Live Demo

CW PSK31 RTTY

JT65/JT9

CW Skimmer from DXAtlas Radioteletype (RTTY) Mode

• Originated to support electromechanical teleprinters connected by wire

– First system installed 1849 between Philadelphia and NYC

• US Navy tested using radio from an airplane in 1922

• 5-bit code (Baudot) represents the alphabet • RTTY uses Frequency Shift Keying (BFSK) modulation

• 1 and 0 bits sent using 2125 hz and 2295 hz tones

• Bandwidth is 250 hz

• All characters are upper-case RTTY Mode

RTTY (note 2 different carrier frequencies) RTTY Mode

(3) Decoded frequency under cursor

(2) Select desired signal (1) Select RTTY modem

FLDigi Software RTTY Mode

User can type here to interactively transmit text

Macros can be used to send messages without any typing Live RTTY Demo

RTTY PSK Mode

• Phase-Shift Keying (PSK) modulation

– Phase shifts an audio tone (shift is audible to computer but not your ear) – Uses 31 Hz bandwidth (actually less than CW!)

– PSK31 designed for typing speed (32 bits/sec, 50 wpm)

• Multiple variants are used

– BPSK (Binary Phase Shift Keying) most frequent, no error correction

– QPSK mode adds forward error correction PSK Mode

Frequent characters don’t require 5th bit

• 5-bit code (Baudot) and Varicode, frequently used characters are shorter

• Supports Upper/lower case, backspace • Low-power (typically < 20W) PSK31 Mode

PSK31 PSK31 Mode

Multiple decoded frequencies

Select PSK31 Modem Matching search string

Characteristic start and end patterns Live PSK31 Demo

PSK31 JT9 and JT65 Modes

• JT65 was developed for weak signal moon bounce use

• Excellent for low power and bad conditions • Uses sophisticated digital signal processing

• Data is sent multiple times for redundancy

• Up to 80% of data can be lost, and still be delivered

• JT65 uses a 1270.5 hz syncronizing tone with 64 additional tones to carry the data JT9 and JT65 Modes

• Station clocks must be syncronized to within 2 seconds

• Each transmission lasts 46.8 seconds • Stations take turns transmitting/listening on odd or even minutes

• Each transmission only sends up to 13 characters

• JT9 is 2 db more sensitive than JT65, and uses less than 10% of the bandwidth JT9 and JT65 Transmissions

• QSO consists only of callsign, signal report, and gridsquare

– Total QSO takes minimum of 6 minutes

• CQ K2RAS DN70 K2RAS calls CQ with gridsquare

• K2RAS PY2XX EN10 PY2XX responds with gridsquare • PY2XX K2RAS R-09 K2RAS responds with signal report

• K2RAS PY2XX R-13 PY2XX responds with signal report • PY2XX K2RAS RRR K2RAS signs off QSO

• K2RAS PY2XX 73 PY2XX signs off QSO JT9 and JT65 Modes

JT9

JT65

JT65 JT9 Live JT9 and JT65 Demo Summary of HF Digital Modes

Mode Modulation Error Corr Speed Bandwidth Comments

CW Amplitude Shift NONE Up to ≈ 50WPM < 100 Hz Minimal equipment

PSK31 PSK Phase Shift QPSK Supports FEC 31 char/sec 31 Hz Popular mode, good for weak signal

RTTY FSK (2 tone) NONE 60 WPM 250 Hz Popular mode, no error correction

JT65 MFSK 65 tones FEC 15 char/min 175 Hz Decodes signal below noise floor

JT9 MSFK 9 tones FEC 15 char/min 15 hz Resistant to fade

Olivia MSFK various FEC 2-3 char/sec 250 – 2000Hz Decodes signal up to 14db below noise floor Example of RTTY (Digital) Congested Contest

CQ Worldwide DX Contest, RTTY Sep 2015 Best Practice - Working Split

• An operator may work in ‘split’ mode to help with congestion

– Lets say a DX operator calls CQ from Timbuktu, so immediately 100 other stations try to contact the DX station on the same frequency…

• On the same frequency, the DX operator cannot distinguish between the 100 callers, and the other 100 stations cannot hear the DX station.

• The DX station may then say they are working ‘10-up’, implying they are listening in a range around 10 khz above their transmit frequency

• This spreads out the calling stations in frequency so the DX station can hear them, while it keeps the DX station on a separate frequency so it is not covered by stations trying to contact him. Best Practice - Working Split

DX station thanks and calls CQ Local stations Single station responds With good DX cadence DX station calls single station Stations respond on range of freq DX station calls CQ ‘up 2’ Working Split – Bad Practices

Local stations not respecting DX cadence Working Split – Bad Practices

Local station doesn’t work split (BAD) Best Practice – Using Filters

(Notch Filter) Best Practice – Using Filters

• Filters can improve performance by

– Removing partially overlapping signals – Improving signal to noise ratio on weak signals

– Improve software decoding of digital signals

– Improving AGC performance

• Filters come in two types

– Physical crystal filters ($$$) – Software defined filters (on Direct Sampling SDR) Lowpass Filter Example Removing an SSB Overlapping Signal

2.7K Filter

2.7k filter picks up part of the adjacent signal 2.4K Filter Bandpass Filter Example Wide Bandwidth = High S/N

2.4k filter is much wider than a single signal Bandpass Filter Example Wide Bandwidth = High S/N

2.4k filter passes 2.4khz of noise in addition to a single signal Narrow Bandpass Filter Example Narrow Bandwidth = Lower S/N

50hz filter is much narrower, removing most noise and adjacent signals

50hz

2.4khz Best Practice Weak Signal Propagation Reporter (WSPR)

• Useful tool to find open propagation paths

• Used to verify your actual transmit performance

– Sends beacon signal containing callsign, grid locator, power level

– Compresses data, 4-FSK modulation, uses FEC

– Effective with s/n as low as -28 db

• Signal reports available on the Internet global map Weak Signal Propagation Reporter (WSPR)

Power used in dBm 30=1W Weak Signal Propagation Reporter (WSPR)

Transmit power 2w on 30M band 11:00AM local time Requirements for HF Digital Operation

• An HF radio!!

– Small number of radios have digital mode decoding already built-in

• Personal computer (Windows, Mac, or Linux)

• Digital mode decoding software on the PC

– Converts audio received on radio to digital data – Converts digital data to audio to be transmitted on the radio

– Popular software: FLDigi, WSJX-X…

• External sound card – (You can use your computers sound card with some limitations) External Soundcard Setup

• External soundcard between the radio and computer

– Eliminates ground loops, which might cause hum or distort the signal.

– Adds PTT and switching the rig audio input from the PC to the mic.

– Adjusts signal level between the radio and computer

– Popular brands: West Mountain Radio, RigBlaster, SignaLink

Audio AFSK vs FSK Soundcard Configuration

• AFSK – Audio Frequency Shift Keying – the PC sends the audio tones to the radio’s mic input.

– Signallink only supports AFSK

• FSK (RTTY) - Frequency Shift Keying – the PC sends a signal (1 or 0) to the radio, where it generates the tones (mark or space), the rig must have a built-in RTTY mode to create the offset tones

• FSK may have lower transmit distortion due to the digital source (1/0) up to the radio Online Sources for Digital Activity

http://www.hornucopia.com Online Sources for Digital Activity

http://www.w1hkj.com/FldigiHelp-3.21/Modes/index.htm Digital Summary Thoughts

• The two most common modes are RTTY and PSK31, start with those

• Limit your power compared to SSB

• Do NOT overdrive your modulation or the signal will be distorted • All software programs use the same PSK decoding routine, so the difference is UI, not performance

• Specialized programs have better performance for RTTY, CW decoding

• Use a generic program like FLDigi before moving to multiple decoding programs Go have digital fun!!! Reference Web Sites

• FLDigi Digital Modes Software – http://www.w1hkj.com

• WSJT-X JT65/JT9 Digital Mode Software – http://physics.princeton.edu/pulsar/k1jt/wsjtx.html

• Log4OM – Logging and Cluster Reporting Software – http://www.log4om.com

• Space Weather – NOAA Space Weather

– http://www.swpc.noaa.gov/communities/space-weather-enthusiasts

• DXSummit – Realtime HF Reported Radio Contacts

– http://www.dxsummit.fi/#/

• QRZ.com – Global Database of Ham Licenses and Personal Pages – http://www.qrz.com

• Signalink External Sound Card – http://www.tigertronics.com/slusbmain.htm

• WSPRnet – Weak Signal Propagation Reporter Network – http://wsprnet.org/drupal/wsprnet/map

• Hornucopia – HF Contest Calendar – http://www.hornucopia.com/contestcal/weeklycont.php Reference Web Sites

• Digital Mode Example Sounds – http://www.w1hkj.com/FldigiHelp-3.21/Modes/index.htm