WB8NUT's Digital Modes Information
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Communication technologies that
are specifically designed to improve "live" HF keyboard
operation can now be achieved which were previously only
theory, too complex, or too costly to implement to be
practical. Thanks to the generosity of radio amateurs (hams)
with programming knowledge, and to the Internet, new and
powerful communications tools are available to all hams. The
evolution and wide spread use of the Personal Computer that
include a digital sound card for Digital Signal Processing
(DSP), is allowing radio amateurs to use these tools to
develop new modes of digital communication. The distinguishing
features of live HF digital operation today are the use of
lower power, compact or indoor antennas and courteous
operating techniques. This reverses the trend of several years
ago.
Confusion over
band space is the obvious down-side as new and old modes
compete for space on the HF bands. Crowding on a single band
like 20 meters is partly to blame for this issue. Fortunately,
the new modes like MFSK16, are designed to improve performance
for a wide range of operating conditions. This should allow
for increased amateur radio band usage to relieve crowding and
extend contact opportunities as propagation changes to favor
different bands. These are really exciting times for all radio
amateurs the use and enjoy all these new digital modes!
An
Overview of Digital HF Radio Operating
Modes
TOR is an
acronym for Teleprinting Over Radio. It
is traditionally used to describe the three popular "error
free" communication modes - AMTOR, PACTOR and G-TOR. The main
method for error correction is from a technique called ARQ
(Automatic Repeat Request) which is sent
by the receiving station to verify any missed data. Since they
share the same method of transmission (FSK), they can be
economically provided together in one Terminal
Node Controller (TNC) radio modem and easily
operated with any modern radio transceiver. TOR methods that
do not use the ARQ hand-shake can be easily operated with
readily available software programs for personal computers.
For the new and less complex digital modes, the TNC is
replaced by an on-board sound card in the personal computer.
AMTOR is an FSK mode that is
hardly used by radio amateurs in the 21st Century. While a
robust mode, it only has 5 bits (as did its predecessor RTTY)
and can not transfer extended ASCII or any binary data. With a
set operating rate of 100 baud, it does not effectively
compete with the speed and error correction of more modern ARQ
modes like Pactor. The non-ARQ version of this mode is known
as FEC, and known as SITOR-B by the Marine Information
services.
To
hear what an Amtor signal sounds like, click the icon
PACTOR is an FSK mode and is a
standard on modern Multi-Mode TNCs. It is designed with a
combination of packet and Amtor Techniques. Although this mode
is also fading in use, it is the most popular ARQ digital mode
on amateur HF today and primarily used by amateurs for sending
and receiving email over the radio. This mode is a major
advancement over AMTOR, with its 200 baud operating rate,
Huffman compression technique and true binary data transfer
capability.
To hear what a Pactor signal sounds
like, click the icon
G-TOR (Golay -TOR) is an FSK mode
that offers a fast transfer rate compared to Pactor. It
incorporates a data inter-leaving system that assists in
minimizing the effects of atmospheric noise and has the
ability to fix garbled data. G-TOR tries to perform all
transmissions at 300 baud but drops to 200 baud if
difficulties are encountered and finally to 100 baud. (The
protocol that brought back those good photos of Saturn and
Jupiter from the Voyager space shots was devised by M.Golay
and now adapted for ham radio use.) GTOR is a proprietary mode
developed by Kantronics. Because it is only available with
Kantronics multi-mode TNCs, it has never gained in popularity
and is rarely used by radio
amateurs.
To hear what a G-TOR signal sounds
like, click the icon
PACTOR II is a robust and
powerful PSK mode which operates well under varying
conditions. It uses strong logic, automatic frequency
tracking; it is DSP based and as much as 8 times faster then
Pactor. Both PACTOR and PACTOR-2 use the same protocol
handshake, making the modes compatible. As with the original
Pactor, it is rarely used by radio amateurs since the
development of the new PC based sound card modes. Also, like
GTOR, it is a proprietary mode owned by SCS and only available
with their line of multi-mode TNC
controllers.
To hear what a PactorII signal sounds
like, click the icon
CLOVER is a PSK mode which
provides a full duplex simulation. It is well suited for HF
operation (especially under good conditions), however, there
are differences between CLOVER modems. The original modem was
named CLOVER-I, the latest DSP based modem is named CLOVER-II.
Clovers key characteristics are band-width efficiency with
high error-corrected data rates. Clover adapts to conditions
by constantly monitoring the received signal. Based on this
monitoring, Clover determines the best modulation scheme to
use.
To hear what a Clover signal sounds
like, click the icon
RTTY or "Radio Teletype" is a FSK
mode that has been in use longer than any other digital mode
(except for morse code). RTTY is a very simple technique which
uses a five-bit code to represent all the letters of the
alphabet, the numbers, some punctuation and some control
characters. At 45 baud (typically) each bit is 1/45.45 seconds
long, or 22 ms and corresponds to a typing speed of 60 WPM.
There is no error correction provided in RTTY; noise and
interference can have a seriously detrimental effect. Despite
it's relative disadvantages, RTTY is still popular with many
radio amateurs. This mode has now been implemented with
commonly available PC sound card
software.
To hear what a RTTY signal sounds like,
click the icon
PSK31 is the first new digital
mode to find popularity on HF bands in many years. It combines
the advantages of a simple variable length text code with a
narrow bandwidth phase-shift keying (PSK) signal using DSP
techniques. This mode is designed for "real time" keyboard
operation and at a 31 baud rate is only fast enough to keep up
with the typical amateur typist. PSK31 enjoys great popularity
on the HF bands today and is presently the standard for live
keyboard communications. Most of the ASCII characters are
supported. A second version having four (quad) phase shifts
(QPSK) is available that provides Forward Error Correction
(FEC) at the cost of reduced Signal to Noise ratio. Since
PSK31 was one of the first new digital sound card modes to be
developed and introduced, there are numerous programs
available that support this mode - most of the programs
available as "freeware".
To hear what a PSK31 signal
sounds like, click the icon
HF
PACKET (300 baud) radio is a FSK mode that is an adaption
of the very popular Packet radio used on VHF (1200 baud) FM
amateur radio. Although the HF version of Packet Radio has a
much reduced bandwidth due to the noise levels associated with
HF operation, it maintains the same protocols and ability to
"node" many stations on one frequency. Even with the reduced
bandwidth (300 baud rate), this mode is unreliable for general
HF ham communications and is mainly used to pass routine
traffic and data between areas where VHF repeaters maybe
lacking. HF and VHF Packet has recently enjoyed a resurgence
in popularity since it is the protocol used by APRS -
Automatic Position Reporting System mostly on 2 meter VHF and
30 meter HF.
To hear what a packet
signal sounds like, click the icon
HELLSCHREIBER is a method of
sending and receiving text using facsimile technology. This
mode has been around along time. It was actually developed by
Germany prior to World War II! The recent use of PC sound
cards as DSP units has increased the interest in Hellschreiber
and many programs now support this new...well I mean, old
mode. The single-tone version (Feld-Hell) is the method of
choice for HF operation. It is an on-off keyed system with
122.5 dots/second, or about a 35 WPM text rate, with a narrow
bandwidth (about 75 Hz). Text characters are "painted" on the
screen, as apposed to being decoded and printed. Thus, many
different fonts can be used for this mode including some basic
graphic characters. A new "designer" flavor of this mode
called PSK HELL has some advantage for weak signal conditions.
As with other "fuzzy modes" it has the advantage of using the
"human processor" for error correction; making it the best
overall mode for live HF keyboard communications. Feld-Hell
also has the advantage of having a low duty cycle meaning your
transmitter will run much cooler with this
mode.
To hear what a
Hellschreiber signal sounds like, click the icon
MT63 is a new DSP based mode for
sending keyboard text over paths that experience fading and
interference from other signals. It is accomplished by a
complex scheme to encode text in a matrix of 64 tones over
time and frequency. This overkill method provides a "cushion"
of error correction at the receiving end while still providing
a 100 WPM rate. The wide bandwidth (1Khz for the standard
method) makes this mode less desirable on crowded ham bands
such as 20 meters. A fast PC (166 Mhz or faster) is needed to
use all functions of this mode. MT63 is not commonly used by
amateurs because of its large bandwidth requirement and the
difficulty in tuning in an MT63
transmission.
To hear what a MT63 signal sounds like,
click the icon
THROB is yet another new DSP
sound card mode that attempts to use Fast Fourier Transform
technology (as used by waterfall displays). THROB is actually
based on tone pairs with several characters represented by
single tones. It is defined as a "2 of 8 +1 tone" system, or
more simply put, it is based on the decode of tone pairs from
a palette of 9 tones. The THROB program is an attempt to push
DSP into the area where other methods fail because of
sensitivity or propagation difficulties and at the same time
work at a reasonable speed. The text speed is slower than
other modes but the author (G3PPT) has been improving his MFSK
(Multiple Frequency Shift Keying) program. Check his web site
for the latest
developments.
To hear what a Throb signal sounds
like, click the icon
MFSK16 is an advancement to the
THROB mode and encodes 16 tones. The PC sound card for DSP
uses Fast Fourier Transform technology to decode the ASCII
characters, and Constant Phase Frequency Shift Keying to send
the coded signal. Continuous Forward Error Correction (FEC)
sends all data twice with an interleaving technique to reduce
errors from impulse noise and static crashes. A new improved
Varicode is used to increase the efficiency of sending
extended ASCII characters, making it possible to transfer
short data files between stations under fair to good
conditions. The relatively wide bandwidth (316 Hz) for this
mode allows faster baud rates (typing is about 42 WPM) and
greater immunity to multi path phase shift. A second version
called MFSK8 is available with a lower baud rate (8) but
greater reliability for DXing when polar phase shift is a
major problem. Both versions are available in a nice freeware
Windows program created by IZ8BLY.
To hear what an MFSK16 signal sounds
like, click the icon
Download Digital Mode Soundcard
Software
- Digipan - Great PSK31 Software
(Freeware)
- Hamscope
- PSK31, RTTY, ASCII, MFSK, Packet and CW
(Freeware)
- MixW
- The soundcard based software that does all the modes!
(Shareware - Reasonable)
Need an
Interface between your Transceiver and the
Computer?
WB8NUT
recommends the Donner Digital Interface - Simple, Affordable,
Easy to connect! Works First Time - Every Time Visit Donner Digital
Interfaces by Clicking anywhere on this
text!
The Predominate USA HF Digital
Frequencies Are:
10 Meter Band: 28.110 -
28.125 Mhz 12 Meter Band: 24.920 - 24.930 Mhz 15 Meter
Band: 21.060 - 21.080 Mhz 17 Meter Band: 18.100 - 18.110
Mhz 20 Meter Band: 14.060 - 14.080 Mhz 30 Meter
Band: 10.130 - 10.145 Mhz 40 Meter Band: 7.060 - 7.080 Mhz
80 Meter Band: 3.620 - 3.640
Mhz
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7.0 This site last updated on May 10, 2003 All company
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Copyright © 2003 J. Duffy
Beischel All Rights
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