The 2 level data slicer ('Hamcomm modem') is connected to the discriminator output of your receiver and to your PC's RS232 port. The interface converts
the baseband signal from the discriminator into levels that can be read by your computer's serial port. That should be a 'real'
serial port. An RS232 to USB converter or a PCMCIA/PCI card with one or more serial ports will not work. For use with a USB port, the USB interface has been developed.
The interface is powered from the serial port (lower part of the schematic diagram).