There seems to be confusion about the rear sockets, it is simple. 3.5mm "stereo" jack for SSB, 6 pin mini DIN for FM.

Please check! I think this is correct, I cannot see any way that damage could be done by wrong connections, there are no power contacts, but don't want any blame! NOTE! This interface is not isolated. This increases the risk of having an earth loop and superimposing 50/60Hz hum on your transmissions. Even if isolation transformers are used it is very desirable to have someone  monitor your transmissions to ensure they are clean. Isolation transformers could themselves introduce hum if they were influenced by the field from a mains transformer.

Works for all modes except 9k6 packet, would need different pin on mini DIN (And menu Change) I cater for a TNC on FM by using an inline plug/socket in the lead from the PKT socket.

The only thing to watch out for is not to feed too much audio into the rear sockets. The rig has protection circuits and will not go into transmit mode.Use the mike input and it will let you put too much audio in without protest, although the transmitted signal MAY not be so clean.

Mic is disabled when transmitting from rear sockets, no need for box in mike lead or extra PSU.

Plug to com port also used to connect to CAT. I used the lead from an old serial mouse.

Isolating capacitor 2u2 + to tip of jack.   6 volts or more.

All leads should be screened cable.  Connect the audio in/out to the tips of stereo plugs, (LH channel) then, if input to sound card line in is not sufficient the MIC input may be used. 

The diagram shows my unit exactly, pin 5 of com port is digital ground and ideally should not be connected to audio ground. This may just be connected to the screen of the CAT lead, or leave out the CAT lead if not required.

The audio in/out are paralleled for FM/SSB, seem to work OK. They could be switched if considered necessary, or for only one mode leave out the unwanted connector and switch. (If the SSB mode is not required the 2u2  and 2k2 are not needed)

The potentiometers may not be needed but make it a bit more versatile, one will be needed if the PC MIC input is used. 

Transistor any small NPN eg BC108 Base resistor 2k2. Diode any small silicon eg IN914

Switch is centre OFF so PTT can be disabled, one way for FM other SSB

Isolation transformers/ optocoupler could be added but most people seem to get by without problems using direct connections. Computer QRM that I have experienced has been via the antenna and ground loops rather than the data leads. Some have had problems, these have often been solved by winding the cables through a ferrite ring, 5 turns. An important point to note is that if the ground of the rig is connected by way of the signal/data cables to a computer then, if the ground (Negative) cable to the radio's high current power supply becomes faulty the whole 20 Amps could attempt to return to the power supply through the signal cables! This is a very good case for using full isolation. 

Was built my usual way for small jobs, on printed circuit board with lands formed by cutting with a small broken hacksaw blade. Fits in Plastic 35mm film container.

Sorry, I only have a toy camera! G4ZFQ

Lots of info on web http://f16.parsimony.net/forum28107/index.htm and  http://www.mods.dk/ for example.

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