TM-D710G 'data' port (mini-DIN 6) 1200bps - 9600bps details...
I've taken a careful look through the various manuals for the Kenwood DM-710 series radios, particularly the TM-D710G / GA Service manual.
The mini-DIN 6 "data" connector at the back of the TM-D710 radio chassis (-not- on the control head) is used for data communications with an external TNC or with "USB sound-card" radio interfaces such as the TigerTronics SignaLink or the Masters Communications RA- and DRA- boards.
As with almost all other VHF/UHF radios that can support 9600bps data communications, the TM-D710 radio chassis "data" connector has separate "1200bps" receive and "9600bps" receive-audio output pins, and one transmit-audio input pin. The TM-D710 menu 518 "EXT. DATA SPEED" setting controls how audio into and out of the "data" jack is routed to the corresponding circuitry in the radio.
When menu 518 is set to 1200bps, receive audio after bandpass filtering is routed to the 1200bps rx-audio pin (5 - 'PR1'), and transmit audio from the tx-audio pin (1 - 'PKD') is routed to a stage in the modulator circuit where bandpass filtering will be applied. When menu 518 is set to 9600bps, receive audio immediately out of the discriminator (no filtering) is routed to the 9600bps rx-audio pin (4 - 'PR9'), and transmit audio from the tx-audio pin (1 - 'PKD') is routed to a stage in the transmitter circuitry immediately before the reactance modulator, where no filtering is applied.
There's an important consequence of having two different audio inputs on the data connector for 1200bps vs. 9600bps; if you want to use one "USB sound-card" radio interface to connect to P2P or gateway stations operating in either 1200bps / VARA FM NARROW or 9600 bps / VARA FM WIDE modes, your radio and sound-card radio interface device must both be kept in the 9600bps configuration. Otherwise, you'd need to change the menu 518 setting and the interface cable each time you change from low-speed to high speed data communications. Fortunately, most gateway stations and P2P stations that use a TNC or sound-card radio interface designed for 1200bps operation can accommodate 1200bps connections from stations configured to operate at 9600bps.
A very convenient feature of the Kenwood VHF/UHF external TNC implementation is that the pin 3 'PKS' PTT-control signal will mute the radio microphone when an external TNC or sound-card radio interface keys the radio. This makes voice coordination on a P2P data link simply a matter of keying the microphone when the data link is idle.
Mark - AD7EF
Mark Davis