W6HQ "digital ham radio"


A Short Overview of Modern Digital HF Radio Operating Modes:

TOR is an acronym for Teleprinting Over Radio. It is commonly used to describe the three most popular FSK "error free" operating modes, AMTOR, PACTOR and G-TOR. 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.

AMTOR 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 ASCII or binary data. With a set operating rate of 100 baud, it does not effectively compete with the speed and error correction of more modern modes.

PACTOR is an FSK mode and is a standard on modern TNCs. This is the most popular 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.

G-TOR (Golay -TOR) is an FSK mode that offers a fast transfer rate under good signal to noise conditions by automatically switching to 300 baud. This mode is an advancement over PACTOR with its faster thru-put, extended Golay forward error correction coding and full-frame data interleaving. (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.)

PACTOR-2 is a robust and powerful PSK mode which operates well under varying conditions. It uses strong logic and automatic frequency tracking. Both PACTOR and PACTOR-2 use the same protocol handshake, making the modes compatible.

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. A good, frequency stable transceiver is required. Data is transferred automatically between two linked stations. An interesting feature of this mode is its ability to automatically adjust RF power to the lowest level needed to operate the link.

HF 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.

NOTE: 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 stability.

The Predominate USA TOR Frequencies Are:
10 Meter Band: 28.070 - 28.090 Mhz 20 Meter Band: 14.060 - 14.080 Mhz
12 Meter Band: 24.920 - 24.930 Mhz 30 Meter Band: 10.120 - 10.140 Mhz
15 Meter Band: 21.060 - 21.080 Mhz 40 Meter Band: 7.060 - 7.080 Mhz
17 Meter Band: 18.100 - 18.110 Mhz 80 Meter Band: 3.620 - 3.640 Mhz

The current condition of the eleven year "sun spot cycle" has reduced the usable spectrum for propagation on the HF bands. Although this condition is now slowly improving, the last 2 years of sun spot minimum have thinned out the ranks for all types of HF ham radio activity including digital operation!
Currently, the best frequency band to find HF TOR activity during the day is 20 meters, and 40 meters during the night. We occasionally experience periods of improved ionospheric conditions, allowing HF propagation to occur on the higher bands such as 15 meters and allowing 20 meters to be usable for longer periods after sunset.
Over the course of the next 3-4 years, propagation on all the higher bands will improve dramatically. The new millennium should signal the start of the "Golden Age of TOR" on the HF bands! (How's that for optimism?)



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E-Mail

Name Call E-Mail
Dave W6HQ w6hq@pacbell.net
Michael KM6NP km6np@electronictimes.com

Page By Dave Robinson W6HQ

Last Updated 7/05/05