WEFAX
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WEFAX Mode
General
Facsimile reception (WEFAX) is available with your TNC since the weather facsimile broadcast are
using an 800 Hz FSK shift which is compatible with the Kantronics 1200 baud modem. In order to
receive WEFAX, you must have a program for your computer which will receive 8 bit data from the
TNC and format it properly for display on your computer screen or your printer. Kantronics has
available three terminal programs which meet these requirements – MAXFAX for the Commodore
64 and 128 computers, SuperFax II for the PC and WeFaxWorks for the Apple Macintosh computer.
Background: HF WEFAX Transmissions and Resolution
Many 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 and
charts are often produced by a particular weather service at their own HF radio station site. Two
predominant stations are NAM, the Norfolk US Navy Fleet Weather Service station, and CFH, the
Canadian Forces Halifax station.
Full 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 per minute, but modern
day charts are digitized (placed in computer storage) at the rate of 120 scan lines per minute on a
flat-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 sometimes
transmitted 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 of
the satellites. As mentioned above, many stations generate their own weather charts. Weather
photos 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 transmission
equipment will not support the baud rate needed for full horizontal resolution. The FSK has been
kept, however, to make today's equipment compatible with that produced earlier and received-map
resolution is acceptable.
Finding WEFAX Broadcasts
There are approximately 50 commercial and governmental WEFAX transmitters located in over 20
countries 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: