Kantronics KAM Operation Manual

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Kantronics KAM Operation Manual Manual pdf 35 page image

WEFAX31WEFAX ModeGeneralFacsimile reception (WEFAX) is available with your TNC since the weather facsimile broadcast areusing an 800 Hz FSK shift which is compatible with the Kantronics 1200 baud modem. In order toreceive WEFAX, you must have a program for your computer which will receive 8 bit data from theTNC and format it properly for display on your computer screen or your printer. Kantronics hasavailable three terminal programs which meet these requirements – MAXFAX for the Commodore64 and 128 computers, SuperFax II for the PC and WeFaxWorks for the Apple Macintosh computer.Background: HF WEFAX Transmissions and ResolutionMany of the weather charts broadcast on HF as WEFAX are hand drawn synoptic maps. i.e. a sum-mary of weather conditions, showing such things as atmospheric pressure and surface tempera-ture over wide areas. many of these maps show whole continents or oceans. These maps andcharts are often produced by a particular weather service at their own HF radio station site. Twopredominant stations are NAM, the Norfolk US Navy Fleet Weather Service station, and CFH, theCanadian Forces Halifax station.Full size charts are eighteen (18) inches wide and vary in length from 10 to 18 inches. In pastyears, many charts were generated on a rotating drum at 60 scan lines per minute, but modernday charts are digitized (placed in computer storage) at the rate of 120 scan lines per minute on aflat-bed scanner. The scanner digitizes with a resolution of 96 lines or pixel per inch. So, the maxi-mum resolution of a hand-drawn synoptic chart, when digitized, is nearly 1800 by 1800 pixels!In addition to the temperature and pressure charts, redigitized satellite photos are sometimestransmitted over HF. The sources of most of these satellite weather photos are the National Ocea-nic and Atmospheric Administration (NOAA) operated weather satellites.All WEFAX charts and pictures received on HF come from an HF ground station, not from any ofthe satellites. As mentioned above, many stations generate their own weather charts. Weatherphotos coming from the satellites are received first by a ground station, reformatted and then re-layed by telephone line to the HF transmission site for dissemination.When the WEFAX maps and charts are transmitted on HF, some of the resolution is lost. This oc-curs because the FSK modulation scheme used by all manufacturers of HF WEFAX transmissionequipment will not support the baud rate needed for full horizontal resolution. The FSK has beenkept, however, to make today's equipment compatible with that produced earlier and received-mapresolution is acceptable.Finding WEFAX BroadcastsThere are approximately 50 commercial and governmental WEFAX transmitters located in over 20countries around the world. Most broadcast on HF (between 3 and 30 MHz). Many broadcast con-tinually while others are on a sporadic schedule. You will nearly always find the following if iono-spheric conditions permit: