Kantronics KPC–3 Plus User Manual
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137WEFAX ModeOverviewBlack and white weather facsimile charts referred to as ―WEFAX‖ by HF radio operators,have been transmitted by shore stations for years and received by commercial ships,yachts, and radio amateurs. By coincidence, the signal format used for WEFAXbroadcasts, 800 Hz shift key (FSK), is compatible with the modem housed within mostKantronics TNCs (e.g., KPC-3, KPC-3 Plus, KAM Plus). In order to receive WEFAXcharts, which are typically hand drawn maps of atmospheric pressure, surfacetemperature, or wind velocity/direction over a wide range of sea, you must use a specialprogram for your computer. Such programs enable your PC to receive 8 bit data fromthe TNC and format it properly for display on your computer screen.These maps, unlike satellite photos with a full gray scale range, are often produced by aparticular weather service at their own site. Two predominant stations are NAM, theNorfolk US Navy Fleet Weather Service station, and CFH, the Canadian Forces Halifaxstation.Background: HF WEFAX Transmissions and ResolutionFull-size charts are eighteen (18) inches wide and vary in length from 10 to 18 inches.In past years, many charts were generated on a rotating drum at 60 scan lines perminute, but modern day charts are digitized (placed in computer storage) at the rate of120 scan lines per minute on a flat-bed scanner. The scanner digitizes with a resolutionof 96 lines or pixels per inch. So, the maximum resolution of a hand-drawn synopticchart, when digitized, is nearly 1800 by 1800 pixels!When the WEFAX maps and charts are transmitted on HF, some of the resolution islost. This occurs because the FSK modulation scheme used by all manufacturers of HFWEFAX transmission equipment will not support the baud needed for full horizontalresolution. The FSK format has been kept, however, to make today‘s equipmentcompatible with that produced earlier, and received-map resolution is acceptable.Finding WEFAX BroadcastsThere are approximately 50 commercial and governmental WEFAX transmitters locatedin over 20 countries around the world. Most broadcast on HF (between 3 and 30 MHz).Many broadcast continually while others are on a sporadic schedule.These are some typical frequencies where WEFAX signals can be found, if ionosphericconditions permit:LOCATION FREQUENCIES (MHz)Halifax, NS 4.275, 6.630, 9.890, 13.510Norfolk, VA 8.080, 10.865, 16.410San Diego, CA 8.646, 17.410Mobile, AL 9.158San Fran, CA 4.346, 8.682, 12.730, 17.151 |
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