1. The amplifier's T/R-control input for the antenna relay is called 
"KEY-IN". When in OPERATE mode, on this input appears a DC signal that is to 
be held low to activate the amplifier to the transmit mode. This can be done 
via either a relay contact or a semiconductor (transistor or integrated 
circuit) with suitable polarity (plus to the ground).


NOTE: You should prefer a semiconductor output when it is available on your 
transceiver, since relay contacts on some models are slow with respect to 
their RF output. You may see a "Hot-Switching Warning" or "RF detected at 
wrong time" message otherwise. This message means that an eventual hot 
switching has been prevented by the amplifier's protection system. You should 
change to the semiconductor output in such conditions. In addition, utilizing 
the semiconductor output, you may disable the transceiver's relay clicking 
(on some models there is a switch intended for a case when the relay is not 
needed).

The electrical specifications of the amplifier's KEY-IN input are as follows:


- Switching voltage (open circuit): 15V max (12V typ.), plus to the ground; 

- Closed-circuit current: 15mA max; 

- Voltage drop / resistance of the control output @ 15mA (closed circuit): 
1.5V/250 Ohm max.

You can control the KEY-IN signal in two different methods. Look at (3) for a 
second way.

For the preferred mode, you have to connect the KEY-IN socket to the 
transceiver's output that goes to the ground when you transmit. Practically 
all transceivers have such an output, and their electrical specifications 
exceed the amplifier's requirements. Transceivers producers give different 
names to this output, and they are for instance: TX-GND, SEND, *T/R-LINE, 
KEY-OUT, etc.


Some transceivers require that their signal "ground on transmit" be 
implemented via a software command, or by changing of a switch on the rear 
panel, or interior of the transceiver. Some models generate a "+12V on TX" 
signal. Then, you may need a simple n-p-n or n-mos transistor, controlled 
through a 10kOhm resistor to the base or gate, in order to "invert" the 
available signal in a "GND on TX". Look in your transceiver's manual or 
contact your dealer or ACOM directly for details about a particular model. 

Please use always shielded cables for these connections.

2. The KEY-OUT socket on the rear panel is a "phono" type (RCA) connector. 
When you don't use the second method of the connection (see p.3), this is an 
extra output signal from the amplifier, that could be either used or not. 
When used, it would improve the T/R process of switching and would increase 
the exploitation reliability.

The KEY-OUT output is usable when the transceiver has available a respective 
input to disable transmitting when the amplifier may need it. If your 
transceiver has no such input (for instance ICOM models), or you use the 
second way of the KEY-IN connection (p.3), please don't worry: the amplifier 
will be fully protected and will function normally, so the KEY-OUT may remain 
unused. 

If your transceiver however possesses a suitable input that is capable to 
disable transmission, we recommend that you utilize that feature. Just 
connect this input of the transceiver to the KEY-OUT socket of the amplifier. 
Transceiver producers give different names to this input, and they are for 
instance: TX-INHIBIT, MUTE, LINEAR, KEY-IN, etc. It is available sometimes on 
BAND-DATA, ACC, EXT, LIN, ATU, and etc rear-panel connectors. Some 
transceivers may require that a "transmit disable" function is implemented 
via a software command, or by changing of a switch, or via adding an external 
pull-up resistor, etc. Look in your transceiver's manual. You have to use the 
preferred connection of the KEY-IN socket (p.1) to utilize this feature.


The output KEY-OUT of the amplifier is an open-drain circuit and it can hold 
a positive DC signal to the ground. During all the periods when the amplifier 
is ready to transmit, this line will always pattern the requests "GND on TX" 
in order to enable transmission. When transmitting is not permissible, the 
output becomes open (for instance, while the antenna relay is in process of 
switching-over) and the transceiver would stop RF driving.


The electrical specifications and timing of the amplifier's KEY-OUT output 
are as follows:

- Switching voltage (open circuit) - up to +50V, 

- Switching current (closed circuit) - up to 20mA, 

- Internal resistance @ 20mA (closed circuit) - 120 Ohm max,

- Delay time - 5ms max (2...3ms typically).

While the amplifier is not powered, and in STANDBY mode, this output is 
directly connected to the KEY-IN socket. Thus, the amplifier will send back 
the "ground on transmit" signal to the "TX enable"-input of the transceiver 
always during OFF and STBY modes in order not to disable any transmission.

In OPERATE mode the signal KEY-OUT will pattern the signal "ground on 
transmit" that is coming on the socket KEY-IN, always when the antenna relay 
is in safe position and when no other warning is present. The signal KEY-OUT 
will reject transmitting if the amplifier detects any risk condition.


Besides, the amplifier contains an independent self-protection that looks 
after the relay safety during a T/R-switching, regardless of taking or not an 
advantage of the KEY-OUT signal.

3. If your transceiver has not a suitable connector providing an output 
signal "ground on transmit" nor "+12V on transmit", you can use the second 
connection method as described below.


Connect the PTT or CW-keying contact to the amplifier's socket KEY-IN on the 
rear panel. Then connect the amplifier's socket KEY-OUT to the input PTT or 
CW-KEY of the transceiver. Always use shielded cables for these connections.


CAUTION: Please check up, that the parameters of the signals PTT and CW-key 
of the transceiver met the specifications of the "KEY-OUT" output of the 
amplifier (see p.2 above). Some very old transceivers models may require 
buffering if the requirement is higher than 50V/20mA.

With the second way of connection, the amplifier will just pass the PTT or 
keying signal directly to the transceiver always when powered off and during 
STBY mode. During OPERATE, the signal will pattern your PTT/keying after the 
antenna relay reaches a safe position, and will disable transmission during 
relay's motion as well as during any risk condition.

The second way of controlling the transmit/receive process could be very 
useful also if the transceiver has an incorrect timing sequence of its T/R 
signals. For instance, if the RF power appears before a "ground on transmit" 
is fed to the amplifier.