The DK9RR-modem: A single chip FSK modem
The DK9RR modem is our newest FSK modem design. It was mainly developed
by DK9RR in close cooperation with the BayCom team. All digital functions of
a standard (G3RUH-compatible) FSK modem were programmed on an 68HC705 microcontroller. This reduces the costs for such a modem significantly,
because only the controller and some analog filters are required. Not even
an EPROM for the FIR filter is necessary, the filter is calculated by
the processor in real time!
The modem has a standard baudrate of 9600Bd, a 19200 bd version will be
available in several weeks. It features four different filter charcteristics
and comprehensive test modes to check linearity and quality of the
transmission chain.
The modem is designed to be used as low cost 9600Bd modem on the USCC>4
slotcard, but it can be operated standalone, too. It has a 2*10 pin
interface (DF9IC standard) on digital side and a 2*5 pin interface
for audio. It consumes 30mA at 5V operating voltage. It is available
as a kit or assembled unit, boards and processor itself are also
available.
The photograph shows the modem (50 * 90 mm in size) with the processor
(bottom center). The other 3 ICs are the D/A converter, an OpAmp for
the filters and a comparator for signal regeneration.
