This program decodes HF and VHF packets It uses HamComm (or similar) interface The audio signal from a receiver in connected to one of the COM ports (DSR line) via 'Ham Comm' style interface which 'squares audio signal by mean of a simple comparator. Comparator output steers RS232 DSR input Each transition on DSR makes an interrupt. Interrupt service routine reads the system timer (8253) so to find out what time elapsed since previous transition. This way the program keeps track of the audio signal period, frequency and timing Ones you have frequency it is possible to decode bits from it find out X25 starting flag, build complete frames, etc In HF mode the program is "hardwired" to 700 Hz center frequency It is intended to be used with 500 Hz CW filter. Precise better than 50 Hz) tuning is required In VHF mode it accepts FSK centered at 1700 Hz with deviation either 800 Hz or 1000 Hz
