Digital Modes

K4LRG

Themes of This Presentation

• General Information: Why do digital?

• Technical: some highly technical discussion • Practical: How to get started?

• Focus: on sound-card modes (no TNC) • Focus: on newer modes (not RTTY or Packet)

Why Digital?

• Fun of Experimentation • Use of computers along with ham radio • Excitement of being on a cutting edge • As technical as you want to get • Relevant to emergency response

ASCII Character

How BPSK31 Works

Varicode Encoder (Huffman Code) Ensures Reversals Even during Idle Binary Phase Reversals Balanced Modulator Carrier Transmit Side ASCII Character Varicode Decoder (Huffman Code) Extract Tone at Baud Rate Synchronization Signal Receive Side No Error-Correction

Varicode

More than 2 phases: QAM

From Binary To Multi-PSK (WINMOR, PACTOR, DRM, Etc.)

EasyPal Example

From:

[email protected] on behalf of kn6kb [[email protected]]

Sent: To:

Tuesday, October 27, 2009 12:46 PM [email protected]

Subject:

[WINMOR] Re: Anyone seeing 8car 16PSK mode?

WINMOR's PSK16 mode is about 50% higher throughput than the 8PSK mode (3 user bits/symbol vs 2). This requires a "good" signal but a "good" signal is more than just high S/N.

PSK is drastically affected by multipath (two or more "copies" of the signal arriving at the antenna via different paths) and 16PSK is more susceptable to this than 8PSK or 4PSK. WINMOR will attempt to go to 16 PSK if there are sufficient ACKs on 8PSK. If the shift to 16PSK does not yield a high enough ACK percentage it will ratched back to 8PSK and "raise the bar" for the next attempt to go to 16PSK. So if you see the system working at 8PSK and the signal is strong but has heavy multipath (fuzzy symbol groups) 16PSK is probably not possible or at least probalby not faster (NET after repeats) than 8PSK.

We have seen and measured many successful 16 PSK session both over the air and through the HF simulator but normally not with poor multipath propagation condtions.

Part of the beta effort is to fine tune the gear shift (mode shifting) algorithm to yield the fastest net throughput for the channel conditions.

Rick KN6KB

HF Timing - Long Path DX

• • • Can interfere with PSK detection Up to 60 ms difference between short and long paths BPSK31 operates at 31.25 BPS, or 1 bit per 32 ms

Weak Olivia Example

How Olivia 1000/32 Works

31.25 MFSK Tones per Second – 32 different tones 5 7-Bit ASCII Letters* Into 64-bit vectors … 64 tones sent in sequence from set of 32 (32 = 2^5) Transmit Side 64 tones At 31.25 tones/sec = 2.048 seconds per 5 letter block Coded by Walch-Hadamard Transform One 32-bit tone Encodes each 5-bit column Inverse Walch-Hadamard Transform Pick Highest Amplitude Tone FFT Receive Side 5 7-Bit ASCII Letters* Populate 64-bit vectors a column at a time Picking greatest amplitude vector each column * Scrambled to minimize false lock with pseudo-random sequence ()xE257E6D0291574EC Two layer “1-out-of-N” FEC code: 1) Highest amplitude tone out of 32 2) Greatest amplitude vector of W-H transform (Viterbi decoder?)

How to calculate Olivia bit-rate

Spectrum of one pure tone Tone modulated by fmod 32-Tones modulated by fmod freq fc Bit rate – Frequency relationship . . . . 1 0 1 0 fc 2 x fmod width freq 32 evenly-spread modulated tones define a bandwidth freq 2 bits ~ 1 cycle Bandwidth / # tones = bit-rate 1000/32 = 31.25

500/8 = 62.5

Olivia Modes

• • • • • • • Unconnected – Unlike WL2K, WINMOR, Packet Manually-controlled – RX-TX specified by sender Message-asynchronous – Not specific to messages – Unlike WL2K, WINMOR Symbol-synchronous – Groups of characters used to form blocks Simplex – One way at a time Chat Mode – Unformatted interchanges With FEC – Two-level FEC

FORMAT

500/16 1000/32 500/8 1000/16 500/4 250/8

TONES

16 4 8 32 8 16

BAND WIDTH (Hz)

500 1000 500 1000 500 250 19.5

24.4

29.3

39.1

39.1

14.6

SPEED (WPM) DECODE S/N RATIO -dB BAUD

13 12 11 10 10 14 31.25

31.25

62.5

62.5

125 31.25

WINMOR

• • • • • • • Connected Automatically-controlled – RX-TX specified by protocol Message-synchronous – Specific to messages Symbol-synchronous – Groups of characters used to form blocks – Like Olivia Simplex – One way at a time – Like Olivia Non-Chat Mode – Formatted interchanges according to an ARQ protocol With FEC – Multi-level FEC – Like Olivia

Comparison of Some Popular Modes in ARQ Environments

1 .5

0

Target For WINMOR Assumptions: 1) 70% ARQ efficiency (typical of Pactor) 2) 3) Max RAW data rate (good channel assumed) 200 Hz guard band used in bandwidth calculations. (allows automatic connections)

WL2K Example

Implementation Details WINMOR DSP Processing Diagram

WINMOR “Virtual TNC” Screen Capture: 15 Carrier QPSK Connection State Frame Type Bytes Received QPSK Constellation (heavy fading) Each pixel = 1 symbol “M” recovery after Summation (memory ARQ) “m” no decode, Good ID (added to summation) “+” decoded OK 2KHz waterfall “-” no decode, poor ID match (not added to summation)

How to Get Started

• Computer – Windows XP or greater • Software for sound-card modes – MIXW (trial is free, full-function app is not) – FLDIGI (free) – DRM780 (free) • Sound Card Interface – Any – Find out sampling rate!

– Some software allows adjustment to this rate, some do NOT • Getting it all set up (how to connect it all up) • Where to find digital modes on the bands

The Basic Digital Setup

External speaker HF Rig 14.069.05

LINE IN MIC IN = Isolating transformer SPEAKER RX cable OUT LINE OUT TX cable PC Connecting up your rig

Computer Transceiver Receive Transmit COM Port PTT

Another Example: RigBlaster Plug & Play

Popular Band Places for Digital

• BPSK31 – 1.838, 3.580, 7.035, 10.140, 14.070, 18.100

– USB • Olivia 500/8 – 1908.75, 3577.75, 7073.25, – USB, 750 Hz Cf

FCC Rules on Data

• • In its 2006

Omnibus R&O

, the FCC revised the definition of data to include certain image emission types in order to permit amateur stations to transmit both image and data emission types in the same frequency segments. The … Commission proposed this change in response to a rulemaking petition filed by Miller in 2003: “The Commission agreed with commenters, including Miller, who argued that permitting images to be transmitted on data emission frequency segments would allow Amateur Radio to make the most of new software programs, thereby advancing Amateur Radio technology, which would be consistent with one of the purposes of Amateur Service, namely to contribute to the advancement of the radio art.” The FCC stated that their rules “do not specifically limit the permissible bandwidth for RTTY and data emissions in the amateur HF bands.” Instead, the Commission continued, Section 97.307(f) limits specified RTTY or data emissions “to a symbol rate not to exceed 300 bauds (in the 80 to 12 meter bands) or 1200 bauds (in the 10 meter band); or for frequency-shift keying (FSK), to a maximum frequency shift of 1 kilohertz between mark and space.”

§97.309(a)(4) Technical Descriptions http://www.arrl.org/FandES/field/regulations/techchar/

This is a one-stop Web site for technical characteristics called for in FCC rules § 97.309(a)(4), which reads:

(4) An amateur station transmitting a RTTY or data emission using a digital code specified in this paragraph may use any technique whose technical characteristics have been documented publicly, such as CLOVER, G-TOR, or PacTOR, for the purpose of facilitating communications.

Documentation should be adequate to (a) recognize the technique or protocol when observed on the air, (b) determine call signs of stations in communication and read the content of the transmissions. Click on names of the techniques already documented: CHIP64 CLOVER (61,588 bytes, PDF file) CLOVER-2000 D-Star Domino (225,010 bytes, PDF file) FDMDV G-TOR (PDF) JT65 (114,422 bytes, PDF file) MFSK MT-63 Olivia (Draft specification provided by the creator of Olivia, Pawel Jalocha, SP9VRC) PACTOR PACTOR-II PACTOR-III PSK31 Q15X25 RWOP WINMOR (PDF) WSPR (MEPT_JT)

Common Pitfalls

• Driving the rig too hard • Driving the rig too long at high tone level • Using audio processing/filtering • Driving the software too hard • Not using macros • Not employing CAT control of rig

Where to Get Info

• • http://kk7uq.com/html/hamfest.htm

http://www.w1hkj.com/ • Mode-specific sites • Sites with samples of modes • Others’ Ham Group Presentations • Mode-specific Yahoo Groups

Good Luck!

K4KRG DigiNet: Tuesday Night 7 PM, 3582+750, Olivia 500/8 Copies of Slides: [email protected]