Kantronics KPC–3 Plus User Manual page 138

Washington, DC
In addition, many of the frequency guides for sale by various radio equipment suppliers
list WEFAX station frequencies.
Tuning WEFAX Signals on HF
WEFAX broadcasters use an 800 Hz shift key (FSK) format, using mark and space
frequencies of 1500 and 2300 Hz respectively. These tones, like voice broadcasts, are
used to modulate the station RF carrier. You can tune these signals with your standard
1200-baud packet modem by tuning about 1.7 kHz below the published station
frequency in upper-sideband (USB). For example, with your HF transceiver or receiver
set to USB, turn the dial until the frequency readout shows 8078.3 to receive NAM (the
Norfolk US Navy Fleet Weather Service transmitting on 8080 kHz).
Receiving WEFAX Transmissions
To receive WEFAX you need to connect an audio cable from your HF receiver to the
audio input of your TNC's 1200-baud radio port. Be sure to read the documentation that
comes with your WEFAX program to learn how to use it.
The WEFAX Command
To cause your TNC to enter the WEFAX Mode, you use the WEFAX command (and
NOT the INTFACE Command).
WEFAX n
This command will cause the TNC to sample the audio input at n samples per second.
The value of n is determined by the number of pixels (dots) which can be displayed
across one line of your terminal screen in the graphics mode. For instance, if the PC
computer you use has 640 dots across the screen and the WEFAX station is
transmitting 2 lines/s (120/min) you should use an n value of 1280. These values keep
your TNC in sync with the HF WEFAX transmitting station. If your WEFAX picture
skews (is not squared up), adjust the TNC clock by using the command DAYTWEAK.
The ABAUD of the TNC must be set to a value at least 5/4 the WEFAX n rate. This
gives the terminal program time to display or store each pixel byte and to handle the
extra start and stop bits added to each set of 8-bits at the serial port.
Exiting WEFAX Mode
To stop the sampling of WEFAX data and return to Command Mode, send a <Ctrl+C>
to the TNC.
4.795, 10.185, 12.205, 14.672
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