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In my handbook it talks about keying the transmitter to produce the dots and dashes. Does this mean that the operator is turning the transmitter on and off, or does this mean that the key is turning the oscillator (within the transmitter) on and off?

EDIT: I am reading my 1976 handbook book

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    $\begingroup$ Ben, would you be kind enough to point us to the handbook you're reading? $\endgroup$
    – Brian K1LI
    Apr 5, 2019 at 23:31
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    $\begingroup$ Similar (but more specific) question: ham.stackexchange.com/questions/13104/… $\endgroup$
    – Kevin Reid AG6YO ♦
    Apr 6, 2019 at 0:13
  • $\begingroup$ Ben, there are newer more recent handbooks. $\endgroup$
    – K7PEH
    Apr 8, 2019 at 5:00
  • $\begingroup$ @K7PEH i scrounge the second hand store for books and what ever i can get. $\endgroup$
    – Ben Madison KO4UXC
    Apr 9, 2019 at 15:20
  • $\begingroup$ Ben, OK, that's fine -- I buy new books unless I am looking for a particular book no longer in print. SDRs are a bit different and that is why I suggested a more recent book. Go to Elecraft and download the user guide for their KX2 transceiver, they describe how DSP is used to generate the CW signal. $\endgroup$
    – K7PEH
    Apr 10, 2019 at 4:30

2 Answers 2

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This block diagram, from the Navy Electricity and Electronics Training Series (NEETS), shows that a buffer amplifier is turned on and off to interrupt the signal from the oscillator to an optional power amplifier and thence to the antenna.

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The buffer amplifier encourages a stable output frequency in two ways. First, by keying the buffer amplifier, the oscillator is always running, so the possibility of frequency instability (e.g., drift) resulting from oscillator temperature changes is reduced. Second, the buffer amplifier provides a stable load to the oscillator output to prevent "chirp" - brief change of the oscillator frequency - when the key is opened/closed.

Of course, a "transmitter" could be as simple as an oscillator that is turned on and off, but such a circuit would be far more likely to suffer from various types of frequency instability, unless it used a very high-Q resonator like a quartz crystal.

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    $\begingroup$ Note that the "triangular" look of the power amplifier output should be smoother, more sinusoidal - we hope! Otherwise the output would be very rich in harmonics, which we definitely do not want. $\endgroup$
    – Brian K1LI
    Apr 6, 2019 at 0:21
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In every case of correctly operating CW transmitters, the RF output is interrupted to produce the pauses between elements, letters, and words.

To a modern ear, the term "Continuous Wave" is slightly misleading -- it doesn't mean the transmitter operates continuously, but rather it's in opposition to the "damped wave" that was produced by spark gap transmitters -- each spark started a pulse of RF energy, which decayed rapidly as losses in the RC circuit sapped the energy. With Continuous Wave, the oscillation has a constant amplitude while it operates; hold down the key, and you'll send a "continuous wave" until you release the key (or burn out something in the transmitter by exceeding its duty cycle limit).

The other misunderstanding here is that there's some other way to send than turning the transmitter off and on. If you stop the RF oscillator in a CW transmitter, you have stopped the transmitter from transmitting, just as you would if you interrupt the signal path from oscillator to amplifier, or cut the power to the amplifier stage. These will all reduce the RF output to zero, and it's switching the RF on and off that makes the "dots and dashes" of CW transmission.

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  • $\begingroup$ To prevent chirp, the oscillator(s) usually runs continuously. Either an intermediate stage or the PA itself (the latter is not so common anymore) is keyed on-and-off with the hand key; when the key is up, there's no RF output. Some transmitters in the early 20th century ran continuously -with full output- to prevent chirp; the key was used to shift the frequency between the RX frequency and an "idle" frequency that was far from the RX passband. Is that what you are referring to? $\endgroup$
    – Mike Waters
    Apr 5, 2019 at 19:19
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    $\begingroup$ No arguments on what's usually done. But answers to this question ham.stackexchange.com/posts/comments/19869?noredirect=1 suggests either can be done, depending on the circuits. $\endgroup$
    – Zeiss Ikon
    Apr 5, 2019 at 19:27
  • $\begingroup$ My 1950s Globe Scout used cathode keying for both the XTAL oscillator and the 6146 final. $\endgroup$
    – Cecil - W5DXP
    Apr 7, 2019 at 14:55
  • $\begingroup$ @Cecil-W5DXP Did it put out a chirpy signal? $\endgroup$
    – Mike Waters
    Apr 7, 2019 at 19:21
  • $\begingroup$ @MikeW As a 15 year old Novice, I didn't even know what chirp was but nobody complained. The Globe Scout schematic is available on the web. $\endgroup$
    – Cecil - W5DXP
    Apr 7, 2019 at 19:49

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