Digital Modes

RTTY,

PSK31

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

PSK 31

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

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.

History

 Simple piece of software that ran under Windows.

 Software available free on Internet  Uses soundcard interface to the transceiver.

History

 PSK31 exploded in the HF digital community.

 Most popular mode for casual QSO’s.

 PSK63 appeared in 2003 and is used by contesters.

What is PSK31?

  31 = bit rate (31.25 baud) ===========================  PSK = Phase Shift Keying 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.

  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

 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

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.

A Digital Station

 Interface – the connection between the computer soundcard and the transceiver.

• Audio from soundcard to transceiver • Audio from transceiver to soundcard • PTT

Interface

 Numerous available on the market • Rigblaster

 RigExpert

Interface

SD Standard Plus

Interface

 Tigertronics SignaLink SL-1+ USB

Interface

 Buxcomm Rascal GLX

 Homebrew

Interface

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

 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

     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.

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



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



ACTIVITY

PSK31 activity found on: • 160M • 80M • 40M • •

30M 20M

• 17M • 15M • 12M • 10M • 6M 1807 kHz (USA) 1838 kHz (Europe) 3580 kHz 7070 kHz (USA) 7035 kHz (Europe) 7028 kHz (Japan)

10138-10142 kHz (Digital Only) 14070 kHz – most activity

18100 kHz 21070 kHz 24920 kHz 28120 kHz 50290 kHz (USA) 50250 kHz (Europe)  Let’s get started…

     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.

 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.



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 <-20 db • Ideally, <-23 • Overdriving can also

final transistors burn out you

W8KRF PSK Station

Digital Signal Reporting



RSQ Reporting

• • •

R

eadability

S

trength

Q

uality • 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.

  

R eadability

• 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

S trength

• S9 Very strong trace • S7 Strong trace • S5 Moderate trace • S3 Weak trace • S1 Barely perceptible trace

Q uality

• 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

Resources

  ARRL’s 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)