PA switching with ICOM transceivers:
By using different ICOM transceivers I found several
times the same problem.
The direct connected output pin for PA
switching from the ICOM transceivers ACC socket
to the PA relay contact doesn’t work. No
ICOM PA's used!
The transceivers switch always in transmit mode after connecting the PA connector.
Most of the tube amplifiers use an open
10 - 36 Volt DC line to the relay connector
(RLY) on the backside. A external relays
contact or an open collector transistor must switch the
RLY point to ground for transmit. All used
ICOM rigs from 1985 up failed!
ICOM Specification for the in/output pin:
- - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
| Input / output pin.
| Ground level : -0,5 to 0,8 V
SEND | Goes to ground when
transmitting. | Input current : Les
than 20 mA
| When grounded, transmits.
|
- - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
So we do have only one pin for input and
output. (Input needs for foot-switches)
If we find two seperate PIN's on different ACC sockets, so it's comfortable but it's only
internal wired to the same point I suppose.)
-Input can be a foot-switch for PTT, simply
switch to ground.
-Any external ground switched signal for
transmit operation.
-In transmit mode the pin switches to ground
level.
What happens in praxis?
-The transmitter switches to transmit by
connecting the PA RLY contact.
(is it possible?)
-The 10 - 28 V open line relay voltage is a
low resistance line and the input of ICOM
transceivers see a low level signal and
switch the transceiver in transmit mode.
First aid:
-A 100-Ohm resistor or two diodes in line
fixes the problem.
-Also my parallel connected foot-switch
works.
But -- that trick doesn’t work with my
IC706 !!!! I had to change the resistance or number of
used diodes.
I am not really satisfied with that and like
to have more engineer work without external relays.
_______________________________________________________________________
Here we go: I found one 4 times opto-coupler in my tinker box and some 50V/1A NPN transistors.
All LED's are connected in series. A 180 Ohm resistor 1/4 Watt completes the series.
The output transistors of the coupler are combined to a darlington switch with the external 50V/1A
transistor.
This way we got a 4 times output switch for any transceiver.
IC 736/7/8:
A connected to pin 7 (13,8V DC) of ACC 1 Socket
B connected to pin 3 (Send ) of ACC 1 Socket
IC 706:
A connected to pin 8 (13,8V DC) of ACC socket
B connected to pin 3 of ACC Socket
TS850 SAT:
A connected to pin 6 (+12V by Send) of the 7 pin DIN-Connector
B connected to ground of the 7 pin DIN-Connector.