Connecting an Icom Transceiver to your PC
PC control of an Icom transceiver is accomplished via a bidirectional CI-V bus, which uses an asynchronous protocol communicated via TTL voltage levels. Thus an interface between your PC and transceiver is required.
The basic function of the interface is voltage level conversion from the RS-232 levels used in a standard serial port (+12 and -12 VDC) and the TTL levels used by your transceiver (+5, and 0 VDC). The interface itself requires power, which can be provided either externally, or with some circuits by using one of the serial port modem control signals as a power source.
There are two decisions that will drive your choice:
1. do you want to use one of your PC's serial ports, or one of its USB ports?
2. would you prefer to build something or buy it?
Being able to choose #1 is a relatively new phenomenon. Previously, controlling a transceiver via USB port meant purchasing a USB-to- serial-port adaptor (e.g. from Belkin or ByteRunner) and connecting it to your interface's serial port. Now, however, there are off-the- shelf USB interfaces; see, for example http://www.microham.com/USB% 20interfaces.html . You can also build one of these yourself, as described in http://www.eham.net/articles/8192 ; if you go this route, be sure to read the comments, as the circuit as presented contains an (easily correctable) defect.
If your PC has a spare serial port, or you'd prefer an outboard USB- to-serial-port converter, then you'll have many more choices with respect to the interface - down both the "buy it" and "build it" paths.
Here are some off-the-shelf products:
You'll find product reviews of the above, along with more alternatives at http://www.eham.net/reviews/products/53 .
You can also purchase a CT-16 from Icom, but they cost twice to three- times more than the above products, and offer no advantage. See http://www.grove-ent.com/CT17.html .
Building a interface is a nice little project that can be accomplished in an afternoon, including the trip to Radio Shack and back. This circuit was published many years ago in QST; its very reliable, and you may already have the necessary parts laying around:
Another nice circuit,
uses the MAX-232 IC for level conversion rather than discrete transistors. It also includes a circuit to control your 706's PTT circuit using one of the serial port modem control signals, which you'll find convenient if you're planning to operate digital modes.
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