Multi Mode Digital Interface
The interface that I built is basically combining 2 individual Interface in one. It uses just one IC and is totally Passive. It takes its supply from the Serial Port and hence the choice of the only IC , IC1, has to be such that it draws less Current. I have chosen to use TLO71 chip.
The Interface has one 5 Pin Keyboard connector which connect to the Rig and on the other hand we have a 9 pin 'D' connector which connects to the Serial Port and 2 Mono pin sockets which connects into the Sound Card of the computer.
I came across a lot of PSK31 Interfaces employ Isolation transformer between the Rig and the Computer, so I built one interface with it. Well A couple of local hams have been trying out experiments without all this and are also successful so I thought of omitting the same in this design.
The 2 presets , PR1 and PR2, in the sound card circuit are used as volume control for the audio coming in or going out from the sound card and I have use 4k7 and 10K respectively. These values can be experimented and used.
Cables have to be constructed for the Rig to the Interface and Interface to the Computer using proper connector suiting UR rig and the computer end.
The above figure shows the pin numbering on the Interface side of the connector . This corresponds to the figures appearing in the circuit diagram of the interface. Pin no. 1 & 3 are connected to each other and Pin no. 4 & 5 are two independent PTT switching points on the Interface. These PTT switching points could be used for HF / VHF and associated resistor values experimented with. TR1 is the PTT switching transistor and could be a BC108 or 2N2222. The 10K preset is used as a volume control for audio thru the serial port. All diodes are 1N4148 type.
This interface offers simplicity in using different modes without having to switch the cables or the Interface.
Modes supported by this simple interface are CW, AMTOR, FAX, Hellschreiber, MT63, PACTOR, PSK31, RTTY and SSTV by simply running the appropriate software which is anyway free on the net.