TS-850S Soundcard Interface with FSK

By Joe K0BX

The Kenwood TS-850S is an excellent transceiver for the digital modes.  It has a heavy duty continuous output of 100 watts.  No need to run at reduced power on RTTY, PACTOR, or PSK31.  Most of the Soundcard interfaces that are on the market use the mike input for transmitting.  Although this has some advantages, it quickly becomes a chore plugging and unplugging the microphone each time you want to switch between SSB and digital.  The TS-850S has a 13 pin accessory plug on the rear of the transceiver that all the connections can be made.  This will allow the microphone to be left connected.

The below diagram shows all the connections.  I got this from the Buck Rogers, K4ABT, website http://www.packetradio.com .  Here you will find not only diagram for the Kenwood TS-850S but all radios.  This site is just loaded with all the information you need to get started.  Buck Rogers sells an soundcard interface that he calls the "Rascal"®.  You can buy it built or in kit form http://www.packetradio.com/psk31.htm.  I bought it in kit form as I wanted to add the "FSK" circuit for RTTY.

R1 = 560 ohm Resistor R2 = 5K variable Resistor  C1 = 1.0uf @25vdc capacitor  T1&T2 600/600 ohm Transformer IC1 = 4N33 or 4N37 opto-isolator for PTT.

This circuit will run all the soundcard program, RTTY, psk31, cw and sstv.  Buck sells the completed kit for $50.00 but you can get a kit with all the parts for $27.00 post paid.  It comes with a nice circuit board that makes assembly very easy.  The only hard part is soldering to the 13 pin connector.  If you think this might be a problem, then I would suggest the assembled kit.  

Adding FSK to this circuit is very easy.  On the TS-850S there is an "RCA" jack labeled "RTTY" on the back panel.  You just need a two wire circuit, tip is the keying voltage and barrel is ground.  Below is the "FSK" keying circuit.  Note that the TXD on the RS-232 connector is the FSK voltage.  This is pin "3" on the 9 pin RS-232 connector (pin 3 on diagram above) or pin 2 on a DB25 RS-232 connector.  You only need a 1K resistor 1/4 watts and a 2N2222A or 2N3904 NPN transistor.  You can get a package of 15 2N3904 transistor from Radio Shack for about $2.29. RS276-1617. NOTE - THIS FSK CIRCUIT PINS 3 AND 5 GO TO THE SAME RS-232 CONNECTOR AS THE INTERFACE ABOVE.  I BUILT THIS CIRCUIT ON A SMALL PERFBOARD AND PUT IT INSIDE THE SAME CASE WITH THE SOUNDCARD INTERFACE.  I DID HAVE TO DRILL ANOTHER HOLE IN THE CASE FOR THE WIRE TO GO TO THE RCA FSK JACK ON THE BACK OF THE RIG.

You should be ready to go, switch the TS-850S to the FSK position.  You need a RTTY software package like MMTTY http://www.qsl.net/mmhamsoft/ to do soundcard RTTY.  Read the on-line manual on how to setup the fsk in the software.  You will also have to set a menu setting in the TS-850S.  Turn the TS-850S off, now turn it on holding the LSB/USB key.  You should be presented with a menu of options.  Each has a number.  Use the memory knob and turn to option 11.  Press the "page down" or "page up" key to toggle the option.  This option sets the FSK keyer polarity.  The "Default" is OFF, but you need to set it to "ON". If someone tells you that you are "up-side-down" when you transmit, you will need to change this menu setting.

Maybe you are wondering why you should run FSK instead of audio tone in the mike like the other modes.  It really doesn't make any different on the other end.  But the big advantage with the TS-850S is that you can select your CW filter from the front panel and the receiving tones will pass with no adjustments.  Also you will be transmitting with a fixed 170 hz shift keyer that is built in.  You will always be transceive with the other station.

Good Luck
Joe K0BX