Unplug the interface, and you should not see any received data.Īlthough we have never encountered this, verifying this internal loopback in Icom interfaces is not conclusive proof that the Icom interface is in fact good. You should see the alphabet being looped back to the port tester. Do not plug the interface into the radio.
Just plug the interface into your serial port. The transmit and receive lines are already shorted internally. If it does not, the interface or cable is bad.įor the Icom line, which uses CT-17, LCU-3-Icom, and other similar circuits, the testing procedure is different because there is no separate transmit and receive lines to jumper together. The alphabet should be displayed in the Received Data field. Now, short the transmit and receive pins on the radio side of the interface together (consult the diagram on this page). Enable Continuous Send in the port tester. This view is from the outside of the connector, looking at the end of the pins.įollow this procedure when testing radio interfaces other than Icom: Plug the interface into the computer port without connecting the radio. Short the pins indicated with red together. They require a connection to an actual radio to provide a small amount of current to the output circuitry. NOTE: A loopback test cannot be performed on the 9-pin Kenwood level converters we sell. On an ATX tower case, COM1 is usually the uppermost 9-pin port. A loopback test is a good way to determine which port is which. We get a lot of tech support calls simply because the customer does not know which port is which. The ports on the back of your computer are often not labeled. If this test fails, your port is bad, loopback connection is incorrect, or it is not the port number you think it is. With the transmit and receive pins shorted together, you should see the alphabet appearing in the Received Data field. Just use the extension cable to extend the port on the back of your computer so you don't have to work behind your computer. An RS-232 extension cable that is known to be good can simplify things. Use micro jumper clips, a larger alligator clip with a nose wide enough to bite both pins, or hold a clean miniature screwdriver over the pins. This chart shows the location of pins 2 and 3 on a 9-pin male connector (the type found on the back of your computer).Ī breakout box is the ideal device for shorting these pins, but they are not easy to find and are fairly expensive. Get a flashlight and look closely, or use the chart provided here. Now, short pins 2 and 3 (the transmit and receive pins) of the serial port together. You SHOULD NOT see anything displayed in Received Data, since you have not yet connected the transmit and receive pins. This will cause the utility to continuously send the alphabet out your serial port.
Select your com port in the port test utility, and click Open Port.Ĭlick Start Continuous Send. This will verify that you have everything set up correctly and are performing the test properly. It is recommended that you first do a loopback test on a known good serial port. It is also useful for determining which COM ports are installed on your computer, and monitoring data transmitted by other devices, testing baud rates, etc.Īfter you run the loopback tester, hold the mouse over the various controls to get help.
This utility is great for loopback testing because it has the ability to continuously send data out a serial port - you do not have to type anything, leaving both hands free to connect the transmit and receive pins on the device being tested.
It will run on any version of Microsoft Windows that has the.
See the link at the bottom of this article. You may save it to your hard disk or run it directly from our server.
The download link is at the bottom of this article. Rather than use Hyperterminal for your loopback test, we recommend using our free one-man serial port tester. If the loopback jumper is in place, and you do not see your typing, something is malfunctoning or the jumper is not connected properly. This tests the port, the level converter device, and any connecting cable. The signal travels from your keyboard, out the serial port, thru the jumper, back into the serial port, and is displayed on the screen. If everything is working, you will be able to type something on the keyboard and see it appear on the terminal window. This is typically accomplished using a terminal program such as Hyperterminal. You may test a radio interface and your computer's serial port using this method.Ī loopback test simply sends data from a port, through a jumper, and back to the serial port.
A loopback test is a simple way to verify that RS-232 communications hardware is working.