I am trying to make a very basic cw transmitter, so far i got a 5V crystal oscillator: A0645147. Whenever I apply voltage to it i can pick up the signal on my handheld however i am not hearing the beep that is associated with the cw morse code. Can anyone suggest what i am doing wrong ?

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    \$\begingroup\$ What frequency is the oscillator, what kind of radio are you using, and what mode are you using to receive the signal? \$\endgroup\$ – W5VO Feb 5 '13 at 1:59
  • \$\begingroup\$ The frequency of the oscillator is 49.408. I am using a handheld yaesu vx-7r in NFM mode. \$\endgroup\$ – user18667 Feb 5 '13 at 2:09
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    \$\begingroup\$ You need to receive it as CW, not NBFM, to hear a tone. \$\endgroup\$ – Leon Heller Feb 5 '13 at 2:41
  • \$\begingroup\$ Leon is right, the 'beep' is a function of the receiver in CW mode. Take a read of en.wikipedia.org/wiki/Beat_frequency_oscillator. \$\endgroup\$ – PeterJ Feb 5 '13 at 3:21
  • \$\begingroup\$ Leon is right, the 'beep' is also called sidetone. \$\endgroup\$ – Chetan Bhargava Feb 5 '13 at 6:50

Traditional CW (as in morse code) transmission is simply on/off keying of an otherwise unmodulated carrier. To receive it as an audible tone, you need a "product detector" which consists of a mixer and a local oscillator at a slightly different frequency, with the audio tone resulting from the difference between the RF frequency and the local oscillator. (Traditionally more advanced receivers convert to an intermediate frequency, filter that (sometimes with several stages of conversion and filtering) and then apply the product detector to the IF; though with software defined radio other schemes are becoming popular)

It seems however that you are trying to use a narrowband FM receiver to hear the signal. An otherwise unmodulated, on/off keyed carrier fed into such a receiver will produce no audio output - it will just activate a power-sensistive squelch and if reasonably strong achieve quieting of static. Therefore, when CW is transmitted to FM receivers (code practice, repeater callsign ID, etc), it's common to on-off key an audio tone fed into the FM modulator - this is often casually referred to as "Modulated CW".

Depending on the stability of your crystal oscillator, you may be able to "pull" it enough with a varactor diode to achieve some modulation by an applied sine wave of 700 or so Hz - I can recall listening to a weather balloon transmitter emitting recorded voice on the 2m FM band by filter-selecting the third multiple of a clock oscillator so modulated (the deviation there would be 3 times what it was at the oscillator's fundamental) .

  • \$\begingroup\$ Good answer. OP's part is a self-contained oscillator module though so he wouldn't be able to pull it. \$\endgroup\$ – PeterJ Feb 5 '13 at 3:57
  • \$\begingroup\$ @PeterJ - while you wouldn't think so, some of these self contained oscillators apparently can be pulled, as Hams found out not long after they hit the surplus market. Especially when it was a harmonic of the nameplate frequency being used, there was enough deviation for a narrowband FM receiver. I also once saw the data sheet for one that was actually marketed as a VCXO with a tuning voltage input. \$\endgroup\$ – Chris Stratton Feb 5 '13 at 4:00

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