TRANSCEIVER / COMPUTER ISOLATION

WHEN USING THE COMPUTER SOUND CARD AS YOUR ' MODEM ' ITS AN EXCEPTIONALLY GOOD IDEA TO MAKE SURE THAT THERE IS NO DIRECT CONNECTION BETWEEN TRANSCEIVER AND YOUR COMPUTER - AT BEST YOU MAY INTRODUCE AN EARTH LOOP -  CAUSING HUM TO APPEAR ON  YOUR TRANSMITTED SIGNAL -   AT WORSE YOU MAY DAMAGE YOUR SOUNDCARD.THE BEST SOLUTION IS TO USE TWO CHEAP AUDIO TRANSFORMERS AND HOUSE THEM IN A PLASTIC BOX -  I ORIGINALLY USED 600:600 OHM LINE ISOLATION TRANSFORMERS - BUT THIS IS AN EXPENSIVE OPTION .THE BELOW CIRCUIT WORKS WELL FOR ME - AND THE TRANSFORMERS ARE LESS THAN £1.50 EACH. YOU MAY NEED TO REDUCE THE AUDIO LEVEL - IN WHICH CASE INCLUDE THE TWO VARIABLE RESISTORS AS SHOWN.IF YOU DO NOT HAVE A HAMCOMM CIRCUIT ON YOUR SERIAL PORT - YOU WILL ALSO NEED TO BUILD A ' PTT ' CIRCUIT - TO GET THE COMPUTER TO SWITCH BETWEEN TRANSMIT / RECEIVE AUTOMATICALLY.

COMPLETE RTTY / PSK INTERFACE

NOTE  - KEEP THE  3 TRANSCEIVER EARTH POINTS SEPARATE FROM THE 3 PC EARTH POINTS - NO DIRECT CONNECTION BETWEEN THE PC AND THE TRANSCEIVER ! OBVIOUSLY THIS UNIT CAN BE USED FOR ANY OF THE DATA MODES, SO IF YOU ARE RUNNING HELL, SSTV, A CW TRANSMIT / RECEIVE PROGRAM, THAN THIS CCT WILL BE OK.

ALTERNATIVE OPTO COUPLER CIRCUIT USING THE SFH618-2 FROM MAPLINS

IF THESE CIRCUITS SEEM NOT TO WORK CHECK YOU ARE USING THE RIGHT COM PORT PIN ( SEE BOTTOM OF THIS PAGE ) SWOP FROM PIN 7 TO PIN 4 - IT WILL DEPEND ON THE SOFTWARE AS TO WHICH ONE IS BEING USED ( PINS DIFFER FROM THE DB9 TO DB25 SOCKET ALSO )

VERY BASIC INTERFACE

ABOVE IS A VERY BASIC INTERFACE, I MUST ADMIT I HAVE NOT TRIED IT, BUT SEE NO REASON WHY IT SHOULD NOT WORK BUT NOTE THAT YOU WILL HAVE A COMMON EARTH CONNECTION BETWEEN THE COMPUTER AND YOUR TRANSCEIVER, SO YOU MAY HAVE EARTH LOOPS CAUSING HUM & SQUAWKS ON YOUR SIGNAL, OR THERE AGAIN YOU MAY NOT ! THIS CIRCUIT MAY BE A GOOD OPTION FOR A QRP RIG RUNING A DIGITAL MODE.

COM PORT PIN NUMBERS