IC-746 FAQ
http://www.qsl.net/icom/download/fes.pdf
http://johnjeanantiqueradio.com/gary.htm
You could build a very simple solid-state switcher like:
http://www.qsl.net/icom/ampcontrol.html
http://www.qsl.net/dxlab/Amp%20Control%20Circuit.jpg
3.5.8
Can't I just use the ACC port to key my amp?
An Icom IC-PW1? Yes. Any other amp? Not directly.
First off, the signal from the ACC ports is from an internal transistor and will only handle a
miniscule load. An external switching circuit will be required.
The SEND jack (RCA phono connector) on the back of the rig is relay operated and is output
only. However, the HSEND and VSEND signals that are available from ACC1-pin-3,
ACC2-pin-3, ACC2-pin6, and MIC-pin-5 are all bi-directional. These leads go to ground
through a transistor when the rig transmits. Actively grounding these leads will put the radio
in the transmit mode.
You'll almost certainly need a solid-state isolation circuit of some sort for this to work
correctly.
3.5.9
How do I build my own SEND relay isolation circuit/relay?
Your design will be dominated by several basic considerations: the voltage/load/polarity
requirements of your amplifier, your choice of SEND jack keying or ACC port keying, and
your choice of relay or solid state switching.
The send relay in the IC-746 (and others) closes 10 to 11 milliseconds before the start of the
RF and opens about 7 milliseconds after the end of the RF. If you use a relay between the rig
and the amp it had BETTER BE FAST. The relay in the amp needs to be closed before the
start of the RF. This means the amp relay AND your intermediate relay together must be
faster than 10 msec.
In general, solid-state systems tend to switch faster than mechanical systems. However, the
relay based systems tend to be easier to design/build and are more versatile.
The line used in the ACC port for this is a bi-directional signal; it does both SEND and PTT
functions. You'll need to account for that in your design.
One example of a relay based design, complete with suppressor diode, bypass capacitor, and
limiting resistor can be found at:
http://www.qsl.net/kk5dr/IcomKeyInterface.html
Rumor has it that Matt will even build it for you; for a fee, of course. But then, you wouldn't
have built your own, would you?
One example of a solid-state design (originally intended for a Kenwood, but easily adapted to
an Icom) can be found at:
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