The new generation of HF HAM Radio !
Special thanks to Richard(NB6Z) for providing
us this helpful information.Thanks Rich.
What you need to start your activity
on Digital Modes?
-Computer and sound card -Software -Interface-HF Radio
and antenna ofcorse
|Communication technologies that are specifically designed
to improve "live" HF keyboard operation can now be achieved that were
previously only theory or too complex to be practical. Thanks to the
generosity of radio hams with programming knowledge, and to the World
Wide Web, new and powerful communications tools are available to all
hams. The evolution and wide spread use of the Personal Computer with
a digital sound card for DSP. The distinguishing features of live HF
digital operation today are the use of lower power, compact or indoor
antennas and courteous operating technique. This reverses the trend
of several years ago...
Confusion over band space is the obvious down-side as new and old modes compete
for band space. 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 ham band usage to relieve crowding and extend contact opportunities
as propagation changes to favor different bands.
An Overview of Modern Digital HF Radio Operating Modes:
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 die-hard operators.
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
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. This mode is becoming a standard for reliable keyboard to keyboard
operation and is available in several popular programs.
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.
is an acronym for Teleprinting Over Radio. It is traditionally
used to describe the three popular "error free" operating 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 TNC 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 these less complex modes, the TNC (terminal node controller)
is replaced by an on-board sound card or out-board audio device. These modes
may use redundancy or "human processing" to achieve a level of error correction.
is an FSK mode that has been fading into history. 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. The non-ARQ version of this mode is known as FEC, and known
as SITOR-B by the Marine Information services.
is an FSK mode and is a standard on modern TNCs. It is designed
with a combination of packet and Amtor Techniques. It is the most popular
ARQ digital mode on amateur HF today. This mode is a major advancement over
AMTOR, with its 200 baud operating rate, Huffman compression technique and
true binary data transfer capability.
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.
is a proprietary mode used for message and traffic handling
over an HF radio circuit. Use of Pactor-III protocol is limmitted for US hams
and some other countries due to the very wide bandwidth of the Pactor-III
signal. Presently digital signals that occupy the bandwidth of PCT-III are
restricted to a few sub bands:
28.120-28.189 MHz, 24.925-24.930 MHz, 21.090-21.100 MHz, 18.105-18.110 MHz,
14.0950-14.0995 MHz, 14.1005-14.112 MHz, 10.140-10.150 MHz, 7.100-7.105 MHz,
or 3.620-3.635 MHz.
Only the embedded hardware (modem) from the German company that owns the rights
to this mode, is capable of operating Pactor-III.
(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.)
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.
PACKET radio is a FSK mode that is an adaption of the very popular
Packet radio used on VHF FM ham 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.
is a method of sending and receiving text using facsimile technology.
This mode has been around along time; the recent use of PC sound cards as
DSP units has increased the interest in Hellschreiber. 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. A new "designer" flavor of this mode called
FM HELL has some advantage for providing better quality print, at the expence
of a greater duty cycle. As with other "fuzzy modes" it has the advantage
of using the "human processor" for error correction.
THROB is yet
another new DSP sound card mode that attempts to use Fast Fourier Transform
technology (as used by waterfall displays) to decode a 5 tone signal. 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.
Frequency-shift keying ( FSK ) shifts between two known states. Phase-shift
keying ( PSK ) changes PHASE of a signal against some reference. FSK is sent
by either shifting a carrier frequency (F1B) or modulating SSB with two shifting
audio tones (AFSK). When sending PSK, a complex audio waveform is transmitted
by SSB. Tracking is much more critical for PSK, thus requiring more frequency
DSP (Digital Signal Processing) techniques use high speed processing to convert
audio into digital coding, so that a program can manipulate the coded audio
in ways not possible with traditional hardware filters. The 16 and 32 bit
sound cards found in modern PCs provide this capability.
FUZZY MODES are those modes that allow the human eye/ear/brain to be used
to its maximum potential. In order to do this, a number of rules are required,
to ensure that any electronics or logic circuitry is not allowed to make decisions
which may be less inspired than human decisions. Examples of potentially Fuzzy
modes are Morse Code, HFFAX, SSTV and Hellschreiber. The rules are:
- The transmissions must be uncoded. (The signal is sent as a real-time
- The receiver must not decide when data is present. (Untouched by any
- The receiver must not decide what data is present. (It must be presented
as received.) A Glossary of TOR TERMINOLOGY
A performance survey of PSK31
vs. MFSK16 modes.