[NLRS] FT-817 RTS-CTS for sequencing transverters

[Doug Reed]

John W0JT sent out a very nice email about sequencing transverters back 
in March. In it he mentioned using the "TX Inhibit" input of the FT-817 
with a sequencer to prevent the radio from transmitting until the 
sequence was complete. He says he would like to see "Request To Send" 
(RTS) and "Clear To Send" (CTS) control lines from the ideal IF radio.

The information about the ACC socket in the FT-817 owners manual is 
minuscule at best, but between the Owner's manual and the schematics 
available on the Internet, it can be seen that the FT-817 does in fact 
have both control lines that John wants. (I don't recall if this was 
specifically mentioned back in March.)

The "TX Inhibit" input has already been mentioned. It is pin 8 of the 
ACC socket on the back of the radio. As long as the input is HIGH, the 
radio will not generate RF. When it goes to ground, you get RF. This is 
the functionality desired for the "CTS" control line John talks about. 
The input is normally held low by an internal pull-down so the radio 
works when nothing is connected to the ACC socket. The external control 
circuit must apply a voltage to the pin 8 input to provide the inhibit 
voltage. I use 12 volts through 10K as the inhibit voltage. I expect 
anything over 1 or 2 volts would work.

The "TX GND" output is the other line of interest. It is on pin 2 of the 
ACC plug. This is an open collector output that goes to ground when the 
radio PTT is pressed. The output even has a protection diode so it is 
suitable for driving a SMALL relay. This provides the "RTS" function 
that John mentioned.

The other important connection is the GROUND connection to pin 3 of the 
ACC socket. Use this line to connect your external control signals back 
to the radio rather than rely on the power supply ground line or coax 
ground. And NO, you should not try to put any high current through this 
pin.

The ACC socket is really convenient. When you press PTT on the mike of 
the FT-817, key the PTT on the DATA jack at the back of the radio, or 
key the CW input, it signals the radio to transmit. On the ACC socket, 
pin 2 goes low to trip an external relay or otherwise signal to begin 
the external transfer sequence. The last step of the sequencer should 
pull pin 8 of the ACC socket to ground to enable the transmitter. For 
high performance, high intercept transverter applications, you will want 
a high performance base radio, but the FT-817 is well designed for 
portable applications.

73, Doug Reed, N0NAS.