Digital Modes

1
Digital Modes

• RTTY, PSK31, Packet, Pactor, Clover,
  Hellschreiber, MFSK, G-TOR, MT-63, Throb, Q15X25

2
PSK 31

• Cousin of RTTY
• Excellent weak-signal performance
• Not error free

3
History

• Created by Peter Martinez, G3PLX
• At first, not very popular because special DSP
  hardware was needed.
• 1999 - Peter designed a version of PSK31 that
  needed nothing more than a common computer sound
  card.

4
History

• Simple piece of software that ran under Windows.
• Software available free on Internet
• Uses soundcard interface to the transceiver.

5
History

• PSK31 exploded in the HF digital community.
• Most popular mode for casual QSOs.
• PSK63 appeared in 2003 and is used by contesters.

6
What is PSK31?

• PSK Phase Shift Keying
• 31 bit rate (31.25 baud)
• Compare to CW
• Simple binary code
• Short pulses (Dits)
• Long pulses (Dahs)
• Communicate the whole English language by
  combining strings of dits and dahs.
• Gaps separate characters and words.

7

• Compared to RTTY
• Still binary
• Instead of on/off (CW), shift frequencies (FSK)
• 5 bits plus start and stop pulses.
• PSK uses Varicode
• Varying number of bits representing each
  character.
• Shorter for often used characters
• Longer for less often used characters

8

• The letter e is used most often and gets a
  Varicode of 11, whereas, E gets a Varicode of
  1110111
• z gets very little use so it has a Varicode of
  111010101 Z gets 1010101101
• Gaps represented by 00
• Two zeros never get used in characters

9
A Digital Station

• What is needed?
• Transceiver most already have one.
• Modem many have them in the form of a computer
  soundcard.
• Software converts binary data from computer to
  modulated audio tones.

10
A Digital Station

• Interface the connection between the computer
  soundcard and the transceiver.
• Audio from soundcard to transceiver
• Audio from transceiver to soundcard
• PTT

11
Interface

• Numerous available on the market
• Rigblaster

12
Interface

• RigExpert
• SD
• Standard
• Plus

13
Interface

• Tigertronics SignaLink
• SL-1
• USB

14
Interface

• Buxcomm Rascal GLX

15
Interface

• Homebrew

16
Interface

• NUE-PSK Digital Modem
• A digital modem for PSK31 field operation ...
  without using a PC!
• The NUE-PSK Digital Modem comes fully assembled
  and tested... just plug in your keyboard and SSB
  transceiver, and start operating!
• www.amqrp.org

17

• How do we generate BPSK signal and transmit
  Varicode over the airwaves?
• Use DSP capabilities of soundcard
• Create audio signal that shifts phase angle 180
  degrees in sync with 31.25 bps data stream
• 0 bit generates phase shift
• 1 bit does not
• Hence, Binary Phase-Shift Keying

18

• When the BPSK audio signal is applied to an SSB
  transceiver we get BPSK modulated RF.
• Only 31.25 Hz wide, narrower than CW.
• Concentrating RF into narrow bandwidth produces
  good reception.
• Receiving station must sync with transmitting
  station (Software)
• Phase transitions are mathematically predictable
  due to the structure of Varicode.

19
PSK31 Software

• Download off Internet
• Many are freeware or shareware with a requested
  donation.
• Popular programs
• HRD/DM780 (IMHO, the best)
• MixW
• Digipan
• MultiPSK
• Others

20
PSK31 Setup

• Receiving (You should be hearing a PSK warbling
  sound. If not, check your sound card volume)
• Panoramic display waterfall
• With no IF or AF filtering the bandwidth on the
  waterfall is about 3000Hz.
• Bandwidth of BPSK signal is 31Hz.
• Many PSK signal can fit in that spectrum
• Vertical lines of varying color/intensity will be
  seen on the waterfall
• Bright strong, faint weaker

21
ACTIVITY

• PSK31 activity found on
• 160M 1807 kHz (USA)
• 1838 kHz (Europe)
• 80M 3580 kHz
• 40M 7070 kHz (USA)
• 7035 kHz (Europe)
• 7028 kHz (Japan)
• 30M 10138-10142 kHz (Digital Only)
• 20M 14070 kHz most activity
• 17M 18100 kHz
• 15M 21070 kHz
• 12M 24920 kHz
• 10M 28120 kHz
• 6M 50290 kHz (USA)
• 50250 kHz (Europe)
• Lets get started

22

• Park radio on frequency of your choice.
• Frequency displayed is Suppressed Carrier
  Frequency (SCF)
• USB range is 2-3 kHz above SCF.
• LSB range is 2-3 kHz below SCF.
• Example Radio showing 14070 kHz USB
• Receiving everything from 14070 to 14073 kHz.
• Place cursor on vertical signal line and click.
• Software selects and decodes the signal.
• When you transmit, the software will generate a
  tone (warble) corresponding to the frequency of
  the selected tone.

23

• Transmitting
• Tone selected creates an RF signal on the correct
  frequency.
• PSK31 is a 80-100 duty cycle mode.
• Most operators run a 20-40 of maximum output.
• Power level is adjusted by the level of the audio
  signal being fed to the input.
• Most accepted procedure
• Set Power to max. (100W for most TRX)
• Apply signal to audio input
• Adjust level to 20-40 (20-40W)
• Overdriving will cause splatter making your
  signal much wider than 31 Hz.

24

• Overdriving
• Indications
• ALC will show activity. There should be no ALC
  indications.
• Goal is to stay in the linear portion of the
  operating curve.
• Some radios will become non-linear at 50 max.
• This is not as noticeable with SSB voice signals
• Shows up as splatter in PSK31 mode.
• Use IMD (Intermodulation Distortion) meter
• Good signal shows IMD of lt-20 db
• Ideally, lt-23
• Overdriving can also burn out you final
  transistors

25
W8KRF PSK Station
26
Digital Signal Reporting

• RSQ Reporting
• Readability
• Strength
• Quality
• Although not yet accepted in Region 2, it has
  been in Regions 1 3 and it is being used by
  some stations in the US.
• It more accurately indicates the quality, as well
  as, strength of the PSK signal.
• Go to www.rsq-info.net for more informaiton.

27

• Readability
• R5 95 Perfectly readable
• R4 80 Practically no difficulty, occasional
  missed characters
• R3 40 Considerable difficulty, many missed
  characters
• R2 20 Occasional words distinguishable
• R1 0 Undecipherable
• Strength
• S9 Very strong trace
• S7 Strong trace
• S5 Moderate trace
• S3 Weak trace
• S1 Barely perceptible trace
• Quality
• Q9 Clean signal no visible unwanted sidebar
  pairs
• Q7 One barely visible pair
• Q5 One easily visible pair
• Q3 Multiple visible pairs
• Q1 Splatter over much of the spectrum

28
Resources

• ARRLs HF Digital Handbook, Third Edition by
  Steve Ford, WA8IMY
• Websites
• www.westmountainradio.com
• www.rigexpert.com
• www.tigertronics.com
• www.buxcomm.com
• www.geocities.com/n2uhc/interface.html
• http//forums.ham-radio.ch/ (HRD)