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?
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•
•
•
•
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
How BPSK31 Works
ASCII Character
Varicode
Encoder
(Huffman
Code)
Binary
PhaseReversals
Balanced
Modulator
Ensures
Reversals
Even during
Idle
ASCII Character
Transmit Side
Carrier
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: WINMOR@yahoogroups.com on behalf of kn6kb [rmuething@cfl.rr.com]
Sent: Tuesday, October 27, 2009 12:46 PM
To: WINMOR@yahoogroups.com
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
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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)
Coded by
Walch-Hadamard
Transform
One 32-bit tone
Encodes each 5-bit column
Transmit Side
64 tones
At 31.25 tones/sec
= 2.048 seconds per 5 letter block
Inverse Walch-Hadamard
Transform
Pick
Highest
Amplitude
Tone
FFT
Receive Side
5 7-Bit ASCII Letters*
Two-layer “1-out-of-N” FEC code:
Populate 64-bit vectors a column at a time
Picking greatest amplitude vector each column
1) Highest amplitude tone out of 32
2) Greatest amplitude vector of W-H transform
* Scrambled to minimize false lock with pseudo-random sequence ()xE257E6D0291574EC
(Viterbi decoder?)
How to calculate Olivia bit-rate
Spectrum of one pure tone
Tone modulated by fmod
32-Tones modulated by fmod
2 x fmod width
freq
fc
fc
freq
freq
Bit rate – Frequency relationship
32 evenly-spread modulated tones define a bandwidth
....
1
0
1
0
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
FORMAT
TONES
BAND
WIDTH
(Hz)
SPEED
(WPM)
DECODE
S/N RATIO
-dB
BAUD
500/16
16
500
19.5
13
31.25
1000/32
32
1000
24.4
12
31.25
500/8
8
500
29.3
11
62.5
1000/16
16
1000
39.1
10
62.5
500/4
4
500
39.1
10
125
250/8
8
250
14.6
14
31.25
– Groups of characters used
to form blocks
•
Simplex
– One way at a time
•
Chat Mode
– Unformatted interchanges
•
With FEC
– Two-level FEC
WINMOR
•
•
Connected
Automatically-controlled
– RX-TX specified by protocol
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Message-synchronous
– Specific to messages
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Symbol-synchronous
– Groups of characters used to form blocks
– Like Olivia
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Simplex
– One way at a time
– Like Olivia
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Non-Chat Mode
– Formatted interchanges according to an ARQ protocol
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With FEC
– Multi-level FEC
– Like Olivia
1
Assumptions:
1) 70% ARQ efficiency
(typical of Pactor)
2) Max RAW data rate
(good channel assumed)
3) 200 Hz guard band used in
bandwidth calculations.
(allows automatic connections)
Target For WINMOR
.5
Pactor 3
Pactor 2
Pactor 1
HF Packet
PCALE
PSK31
0
MT63
(After ARQ overhead)
Net bits/sec/Hz of BW
Comparison of Some Popular Modes in ARQ Environments
WL2K Example
Implementation Details
WINMOR DSP Processing Diagram
WINMOR “Virtual TNC”
Screen Capture: 15 Carrier QPSK
Connection State
Frame Type
Bytes Received
“+”
“M” recovery after Summation
(memory ARQ)
“m” no decode, Good ID
(added to summation)
QPSK Constellation
(heavy fading)
Each pixel = 1 symbol
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
PC
HF Rig
14.069.05
LINE IN
RX cable
SPEAKER
MIC IN
= Isolating transformer
OUT
LINE OUT
TX cable
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 (61,588 bytes, PDF file)
CLOVER
CLOVER-2000
D-Star (225,010 bytes, PDF file)
Domino
FDMDV (PDF)
G-TOR
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
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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
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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: AI4IN@arrl.net