At my radio club, after selling several older transceivers, we managed to purchase two Icom IC-7610 units to upgrade our radio room. Even though they already have an output for connecting a linear amplifier, we decided to build two relay boxes (similar to the previous one made for the FT710) in order to control older amplifiers while protecting and isolating the radio’s PTT output. In this version, just like the previous one for the Yaesu, both an RCA connector and a 6.3 mm jack were added to allow the radio to be keyed into transmit mode externally.
While the Yaesu uses two separate pins, one to control the linear amplifier and one to put the radio into transmit mode, the Icom uses a single pin called SEND. When the radio transmits, the pin is pulled to ground; conversely, when the pin is pulled to ground externally, the radio switches to transmit mode. The wiring diagram is also shown inside the manual in the rear connector pinout section.
This is the schematic: when the radio goes into TX, it powers the relay (+13V and SEND), which then closes the RCA contact to control the amplifier, isolating the radio from higher voltages that may be present in older amplifiers. An RCA connector and a 6.3 mm jack are also added between GND and SEND to externally switch the radio into TX mode.
