Winter 2003 Issue

This paper was originally presented at GippsTech 2002,
the annual Australian Conference designed to encourage participation
in VHF, UHF, and Microwave amateur radio operations. GippsTech is a hybrid name for the technical conference being held at the Gippsland, Victoria campus of Monash University.

By Rex Moncur,* VK7MO

WSJT is a radio communications computer program with a mode, FSK441, which has been designed specifically for meteor scatter. Its performance is such that it allows meteor scatter contacts on 2 meters throughout the year without waiting for showers. It works well in the range 800 to 1800 km, and typically one can complete a QSO in 20 minutes with 100 watts. The program has proven viable for portable operations in activating rare grid squares with contacts up to a little over 2000 km with a small Yagi that can be carried on the roof of a car. (1 km = .6 mile)

The Program

WSJT stands for Weak Signal communication by Joe Taylor, K1JT. It works much like PSK31 and requires a computer with sound card and an interface to an SSB transceiver. The program has two modes:

• FSK441 for meteor scatter
• JT44 for weak, steady signals—i.e., tropo scatter and EME

This paper is concerned with FSK441 for meteor scatter. The mode is called FSK441 because it uses Frequency Shift Keying to send sequential tones of 1/441 of a second, or about 2.3 milliseconds, duration. Characters are sent as three sequential tones selected from four tones. The four tones are 882, 1323, 1764, and 2205 Hz (tones 0, 1, 2, and 3)—for example, the characters A = 101, Z = 231, 1 = 001. In addition, the program uses any one of the four tones sent continuously to represent two frequently used reports— R26 and R27, roger (RRR) and 73. As they are sent continuously, a narrower bandwidth can be used, thus significantly improving performance in completing a contact.

The program sends at around 1800 words per minute and can transfer two callsigns and a report in a tenth of a second meteor ping. This ability to work on very short pings means it can be used on the more frequent underdense pings, allowing contacts throughout the year without waiting for showers. The fact that it can be used throughout the year makes it ideal for activating rare grid squares on 2 meters that are beyond tropo and aircraft enhancement range, up to a little over 2000 km.

Getting Operational
To get operational you need the following:

• 2 meter transceiver and 100 watts, although contacts have been made with 50 watts.
• Single Yagi of 5 to 10 elements, horizontally polarized. Elevation is not necessary.
• Computer of Pentium 75 MHz or better with sound card.
• Interface such as widely used for PSK31.
• The WSJT program, which can be downloaded at <http://pulsar.princeton.edu/~joe/K1JT/>.

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