[Icom] ACOM and ICOM Keying Interface

[Brian Allen]

Actually I had so many responses about the specifics I thought it best just 
to send out the notes that I have.  This is directly from Krassy, who is the 
US Rep. for ACOM in Maryland.  You'll see that you can key directly, BUT it 
has to be done a specific way and with the limitations mentioned.  PLEASE 
don't hold me responsible for what is below, I'm just the messenger ;)

I just went ahead and ordered the cable that I mentioned before, which is 
connected similarly, but does have the relay buffer built in.

73, Brian (N0VSB)

=====================================================================
From:     aa1nd@aol.com
Reply-To: acom-list@yahoogroups.com
Date:     Wed, 30 Jan 2002 14:29:53 EST

For ICOM transceivers, you should preferably use the PTT and CW keyer (and 
parallel computer) connected to the respective inputs of the transceiver. 
For amplifier control use the semiconductor control input/output "HSEND" on 
the round "ACC" connector of the transceiver. For some ICOM models it is 
named "SEND". Connect it directly to the "KEY-IN" input of the amplifier via 
a  shielded cable. You don't need any relay between ICOM transceivers and 
the ACOM1000 or ACOM2000A.

Generally, the HSEND (SEND) signal on the ACC connector of ICOM models is 
bidirectional. If you connect it to the ground, the transceiver will go to 
transmit, i.e. it acts like an external PTT input. A 20mA "output" current 
will flow through your external PTT contact. This direction of the HSEND 
(SEND) however is not used for external amplifiers control. Another function 
of the same signal is an output, that goes to the ground when you activate a 
transmission using the front panel SEND button, mike PTT, VOX, or CW keyer.  
In this direction, it will withstand 100-200mA "input" current (drawn from
amplifier's control input) and is suitable to control ACOM amplifiers.

If you would simply wire the CW key line from your keyer (and parallel
computer) directly to both the Icom and the A1000 (in parallel), the 
amplifier would be OK. Most of the ICOM models would however only change to 
transmit but without emitting any carrier (they would wait for a closure of 
their input "CW KEY"). For SSB, such connection is OK to a foot switch. Note 
however, that the foot switch should be bounce-free since some asynchronous 
timing may arise. You could
also use the foot switch for CW, with the keyer connected to the
transceiver's "CW KEY" input. You will lose however the possibility of 
operation in QSK/FULL-BK-IN mode.

More information about the connections KEY-IN and KEY-OUT follows below. 
Briefly, the amp is keyed by grounding the KEY-IN jack. The keying voltage 
is typically 12VDC and the keying current is less than 15mA. Both amplifiers 
ACOM1000 and ACOM2000A are QSK-compatible with all QSK-capable transceivers 
on the market. The keying circuit requirements for the ACOM1000 and the 
ACOM2000A are identical.

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.

73 Krassy  K1LZ
29 January 2002.












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