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I am trying to create build a morse code transmitter. I know that morse code is sent at 500 KHZ so I set my 555 to spit out pulsating DC in a square wave with 9 volt peaks. But I am unsure wether antennas will transmit pulsating dc. And I also would like to add a couple filter capacitors on the circuit which block dc... but when I try to use a transformer to get ac from my pulsating dc it turns into a sine wave ac....... Any help????

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    \$\begingroup\$ What does an "ac square wave" signal look like...? \$\endgroup\$
    – Shamtam
    Aug 6, 2014 at 22:50
  • \$\begingroup\$ Have you considered just AC-coupling the signal? \$\endgroup\$ Aug 6, 2014 at 23:01
  • \$\begingroup\$ Are you using the 555 to generate your morse code? or to generate the 500 KHz carrier? \$\endgroup\$
    – Phil S
    Aug 7, 2014 at 3:28
  • \$\begingroup\$ @Shantam: In the vernacular, like this: dropbox.com/s/uhvio7cq2vy3xp6/AC%20square%20wave.png \$\endgroup\$
    – EM Fields
    Aug 7, 2014 at 8:17
  • \$\begingroup\$ @user1726: if what EM Fields posted is what you want, just run the 555 off +/-V instead of 0/+V \$\endgroup\$ Aug 7, 2014 at 9:07

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You should feed the antenna with a sine wave to transmit a pure single-frequency signal. A square wave as generated by the 555 will have many harmonics.

Morse code can be transmitted on any frequency. 500 KHz was, long ago, the marine morse code distress and calling channel.

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    \$\begingroup\$ On any frequency, but watch for local regulations :) \$\endgroup\$ Aug 6, 2014 at 23:17
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You should use a low-pass filter at about 600-700KHz (somewhere between the frequency and the first harmonic) to get the output to atleast close to the sine wave. Additionally, a high-pass filter at 1-2Hz can remove whatever DC is left in your signal (turn it into your 'AC square wave', so to speak). You may want to choose your final amplifier in the chain carefully, and make sure it can drive enough energy to give you the signal strength you want.

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