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Receiving and Transmitting Morse Code (CW) With Your Macintosh


Using MultiMode, you can send and receive morse code with your Macintosh. After connecting your Mac to your radio (see our interfacing notes for details on this), fire up your copy of MultiMode and set it for CW (Morse Code) mode.

Next, tune in a station sending CW. When properly tuned in, the tuning display, which shows a spectrum of the received signal, should look something like this:

The peak, which is the received morse code signal, is centered on the red line.

The demodulation display looks like this:

The dots and dashes are plainly visible here. The CW filter in MultiMode is fairly sharp, so proper tuning is required. Many radios also have a tight CW filter, so you want to make sure the center frequency in MultiMode is set equal to that of your radio. Also make sure that the audio level going into the Mac is adequate, without over-driving. We find that having it reach about the midway point on peaks works well.

Next, you want to select the correct speed for the morse code being sent, in WPM (Word Per Minute). You don't need to be very accurate here, being off a few WPM will still produce good decodes. You can also click on the AUTO button to have MultiMode automatically determine and set the speed. This usually works quite well, although it can be fooled by noise.

Decoded morse code characters will now start to appear on your screen. MultiMode can copy machine-sent CW very well. Hand sent morse can be copied if the operator maintains a proper dot/dash ratio, and spacing and speed. Very poorly sent morse code is difficult enough for a human to copy, let alone a computer!

For transmitting morse code, your Mac produces audio, at the same frequency specified as the center frequency. If you feed this audio into your transceiver, and transmit in SSB mode, you will end up transmitting on a single RF frequency, essentially duplicating a CW transmission.

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Chris Smolinski