I decided to use an Ameritron ARB-704 relay buffer to isolate and protect the TX GND (transmit ground) signal from the FTDX 1200 exciter to key my AL-811H linear amplifier via the Relay input.  An adjustable ALC Out voltage is also available from the linear amplifier that can be fed back to the FTDX 1200 to limit the exciter drive to legal and safe levels for the AL-811H.  I also have an LDG AT-1000ProII Autotuner which has a one button manual tuning feature that I wanted to utilize in addition to the full and semi-automatic tuning abilities.  Therefore, I turned my attention to the required interface cabling:

• RCA sockets are located on the back panel of the AL-811H linear amplifier for the Relay keying input and ALC Out;
• RCA sockets are located on the back panel of the ARB-704 relay buffer for the Amp output (to AL-811H Relay input), the ALC and the Radio input (to FTDX 1200 Transmit Ground output);
• ALC and Radio are also available on a 5-pin DIN Multi-Port socket on the back panel of the ARB-704 along with a +8-15V input and GND;
• A 3.5mm stereo socket is located on the back panel of the AT-1000ProII autotuner for the Radio signal that needs to be connected to the FTDX 1200 TX REQ IN input;
• A 10-pin mini DIN LINEAR socket is located on the back panel of the FTDX 1200 for TX GND, EXT ALC IN, TX REQ IN and other signals not in scope.

The problem is that signals from the 10-pin mini DIN LINEAR socket on the FTDX 1200 need to be connected to two separate pieces of equipment – the ARB-704 relay buffer and the AT-1000ProII autotuner.

I didn’t want to have to make some sort of Y-cable, but fortunately there is a spare pin 4 on the ARB-704 5-pin DIN Multi-Port socket.  If I were to route the Radio signal from the AT-1000ProII autotuner via this spare pin, I could make a 5-pin DIN plug to 10-pin mini DIN plug multicore cable to connect all of the required signals between the FTDX 1200 and the ARB-704.

I added another RCA socket on the back panel of the ARB-704 in order to get the autotuner Radio signal into the relay buffer box as the TX REQ IN signal and wired it internally to the spare pin 4 on the 5-pin DIN socket:

Putting it all together:

• A home brew RCA plug to 3.5mm stereo plug shielded cable connects the ARB-704 relay buffer TX REQ IN signal (on the newly added RCA socket) to the AT-1000ProII autotuner Radio signal (not to be confused with the ARB-704 Radio signal):

• A home brew 5-pin DIN plug to 10-pin mini DIN plug shielded 4-core cable connects the ARB-704 5-pin DIN Multi-Port socket to the FTDX 1200 10-pin DIN LINEAR socket:

• A standard RCA plug to RCA plug shielded cable connects the ARB-704 relay buffer Amp signal to the AL-811H linear amplifier Relay signal;
• A standard RCA plug to RCA plug shielded cable connects the ARB-704 relay buffer ALC signal to the AL-811H linear amplifier ALC Out signal.

73 Chris
VK2BYI