I don't "get" CW.

I can't understand the chatter on an FM radio broadcast when my radio is set to AM. This makes sense, the signal is modulated using frequency modulation and I am trying to decode it with amplitude modulation so the result is scrambled nonsense.

Now, I often hear Morse code on the same channels and I can perfectly hear the dots and dashes when listening in FM mode. I guess the simple explanation is that the Morse code was FM modulated at the source, so there is no CW involved here, correct? Did I simply never listen to a CW modulated Morse broadcast?

The reason to use CW is the reduced bandwidth. Does this simply mean it's frequency modulated with a "smaller filter" or is CW really a different modulation type?

You can use AM or FM for voice, depending on the use case. Is this the same for Morse? You can use AM, FM or whatever mode to send Morse but CW is preferred since it's the most efficient mode? If so why do people use CW and Morse interchangeably? Are there any other reasons why you would use CW?

  • $\begingroup$ What radio(s) are you using? $\endgroup$ – Mike Waters Jul 16 at 13:53
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    $\begingroup$ @MikeWaters A simple Baofeng. Scott's answer makes a lot of sense, I didn't realize Morse doesn't need to be audio. $\endgroup$ – Cimm Jul 21 at 18:58

You don't say where you are hearing the Morse code. You say "on the same channels", but don't specify where you are listening.

If you send Morse code using a buzzer, then that generates an audio tone. As with any audio, that can be sent over AM, FM, SSB or any other mode that can send audio.

It is quite common for Morse code to be sent as an audio tone on FM channels usually on the 2m band, to assist people in learning Morse code. This might be becoming less common nowadays, since Morse code is not a licensing requirement in many countries.

However, if you are listening at the bottom of the HF bands, those are CW portion of the bands. There you will come across Morse code being sent using CW, and you will need a BFO to hear it properly. By which I mean you will need to select SSB or CW on your radio to demodulate it.

EDIT: Why would anyone use CW in preference to generating an audio tone and modulating that? Basically because the signal is much simpler - it's a single frequency being switched on and off, and so all the energy in the signal is in that one frequency; there are no sidebands and no signal bandwidth to worry about.

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    $\begingroup$ I suspect the OP is talking about VHF/UHF FM repeaters identifying via Morse code. $\endgroup$ – rclocher3 Jul 16 at 13:24
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    $\begingroup$ That is a possibility. But I’d like to hear more about where they heard it, to be sure $\endgroup$ – Scott Earle Jul 16 at 13:26
  • $\begingroup$ I heard Morse code on our locale repeater (70-centimeter band), I think it's the repeater transmitting their call sign every hour or so. Your edit near the end explains a lot. The Morse code I heard was audio Morse code but CW is not audio, it's on or off, like 0 and 1 in computers. Thanks! $\endgroup$ – Cimm Jul 21 at 18:57
  • $\begingroup$ Repeaters frequently ID with morse code for several reasons. First, it's trivial to generate it, but also, you can mix morse code into voice conversation and leave both readable. $\endgroup$ – user10489 32 mins ago
  • $\begingroup$ Any signal with information has sidebands and a bandwidth. That includes Morse code transmitted via on-off keying of a carrier. It is much narrower that typical voice. Practical bandwidth for Amateur Radio OOK Morse is a couple hundred hertz. $\endgroup$ – WA9ZZZ 30 mins ago

Morse Code is a timed on-off signaling method that is not restricted to CW radio, as it was invented decades before Maxwell hypothesized the existence of radio waves. Morse Code can be used for communicating with clicking relays, buzzers, flashlights, mirrors, eye blinks, printed text, flag waving, Zoom, one or more sound channels of a highly encoded ATSC television signal, etc., as well as RF CW.

CW or continuous wave is when an almost unmodulated (except for rise-fall transitions) single “continuous” radio frequency wave is used to carry an on-off code, sometime not using just standard ISO Morse Code sequences in some regions, where they need a different character set.

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  • $\begingroup$ Thanks! I don't know why I associated Morse code with an audio signal. I spent enough time sending Morse with a flashlight when I was supposed to sleep, how could I forget. ;) $\endgroup$ – Cimm Jul 21 at 19:05

Although what you heard was keyed audio transmitted by FM, you can often hear Morse sent by keying a carrier (OK, Hams call it "CW"), with an FM receiver. It usually requires a relatively strong signal, however.

The receiver goes into "full quieting" during the carrier "on" time, & returns to background "hiss"during the "off" time.

Although this sounds backwards, you hear the "dits & dahs" as distinct sounds, rather than periods of silence, something like "crunch, crunch, crunchity crunch", & can read the Morse from that.

You can also hear the change in background noise for a strong CW signal with your receiver in AM mode.

You mentioned not being able to resolve an FM signal when your Rx is set to AM. This is probably because your Baofeng's frequency intervals are too wide to use "slope tuning". With a continuously tunable AM, or even SSB receiver, slope tuning will allow you to resolve FM quite well, although the quality on wider deviation signals may not be the best.

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