It's the standard 4-pin connector for the Icom AH-4 tuner. The pins are Gnd, +12VDC, and two control pins. One of those signals the tuner with a pulse to start tuning and the other is an input from the tuner to make the radio transmit a 10W carrier. If you want more info take a look at www.ham-kits.com
As far as I know, Alinco is the only other mfg that uses the Icom standard interface (although they use a different connector).
You **might** be able to use the LDG 100 with other radios if you supply it with 12VDC and use the tune button on the tuner and manually key the radio in CW to provide the carrier. Without an Icom compatible interface it won't be able to react with the radio automatically though.