I want to build a portable device (handheld) that receives and transmits Morse code in the form of Radio Frequency. I want the antenna length to be 8 inches or less and would also like a range of up to a half a mile, including inside a building with many rooms.

I want a simple button to transmit Morse. I also want a knob to change the pitch it transmits Morse at. I want the Morse to be heard when you receive it from someone else as well as when you transmit through a speaker.

I'd like to power this with 6 volt maximum, and 3 volt minimum. (I will be using AAA batteries). I don't really care about the frequency, but my friend has an amateur license and I will be getting one soon, so I can transmit on those frequencies.

  • 1
    \$\begingroup\$ I'm going to repost talkingelectronics.com/projects/27MHz%20Transmitters/… from your previous question. 27MHz is quite suitable for this, no licensing issues, crystals are widely available and it works with sensible sized antennae. \$\endgroup\$
    – pjc50
    Apr 4, 2013 at 13:10
  • \$\begingroup\$ I just cleaned up the question a bit, while not being an expert in the area Morse code is normally transmitted as a CW carrier AFAIK and the 'beep' is a beat frequency oscillator (BFO) in the receiver so they may be a few things to look up. \$\endgroup\$
    – PeterJ
    Apr 4, 2013 at 13:16
  • \$\begingroup\$ I still can't see a specific question about electronic design - what exactly is required? \$\endgroup\$ Apr 4, 2013 at 13:26
  • \$\begingroup\$ possible duplicate of Simple Morse code walkie talkie circuit \$\endgroup\$
    – Dave Tweed
    Apr 4, 2013 at 13:28
  • \$\begingroup\$ It won't meet his requirements, though, because of the power limitation. \$\endgroup\$ Apr 4, 2013 at 15:55

2 Answers 2


Assuming you're in the US, the first place I'd look is the Radio Amateur's Handbook. It's available at any library and has exactly what you're looking for: basic radio theory and circuits for transmitters & receivers from trivial to very complex.

If you have a ham license, you can build a simple CW transmitter that's nothing more than a gated sine wave oscillator on the 40M band (bear with me: my ham license (Advanced) expired over 15 years ago and I may get frequencies wrong). Since an 8" antenna is very short at this wavelength, you won't get much range, but a little 50mW transmitter may be enough. However, it's very easy to build a transmitter for this band (7 MHz) so it's a good place to start.

For a receiver, I'd suggest a simple direct conversion one. Adjusting the frequency of the local oscillator will change the audio frequency of the incoming CW signal just the way you want.

I can't attach circuits because I don't have any recent experience with simple circuits that I know will work. Again, I recommend the Handbook because it's an excellent reference. I built exactly what I described above when I was in 11th grade (decades ago :-) and with much easier component availability these days, to say nothing of much improved performance, I expect this would be a nice weekend project for a hobby-level experimenter.

An alternative that doesn't require a license would be to pick up one each of the little 318/434 MHZ transmitter/receiver pairs such as this. You will need to build a little audio oscillator to connect to the digital output of the receiver, but circuits for 555 oscillators are all over the web. These little boards are cheap and very easy to use. However, I don't think you'll get half a mile range from them.

  • \$\begingroup\$ He appears to want sidetone when transmitting, with variable pitch. \$\endgroup\$ Apr 4, 2013 at 20:43

I think you need to refine your requirements a bit. Transmitting Morse code isn't that hard. This is usually done by keying the transmitter on and off. That's what some people erroneously refer to as "CW".

The reason you hear beeps at the receiver is due to how the receiver works. The transmitter is either sending carrier or not sending carrier. Making beeps was usually done by mixing the received carrier with a locally generated signal of just a little different frequencies. The two would mix, or "beat" against each other to produce the audible tone. When the carrier went away, so would the tone.

For example, let's say your transmitter is sending bursts of 27.0000 MHz for the dits and dahs of the Morse code. If the local oscillator in my receiver is set to 27.0004 MHz and mixed with the received signal, a beat frequency of 400 Hz will be generated. I will hear this as a beep every time you send a dit or dah. If I wanted to hear your dits and dahs at a different frequency, I'd adjust my local oscillator accordingly. There is nothing you can do to control the frequency of the beeps I eventually hear.

For a simple homebrew project just to learn and have some fun, I'd do the transmitter as I described. Find some simple RF oscillator circuit and have it enabled when the key is pressed. The whole setup will be hard to debug without a lot already working, so it would be useful if you can get hold of a shortwave radio. Some of those will have a keyed transmission mode built in with the local oscillator creating the beat frequency as I described. Then you can listen to your Morse code transmissions and verify that the transmitter is working. If you can find a old "regenerative" receiver, it will have the ability to make a beep when it receives a certain carrier frequency built in as a inherent part of its operation.

Don't try to go for long distance or high power, especially at first. A transmitter you cook up yourself will likely cause interference somewhere, even if you intend it to be on a band where something is allowed. If you do too much of this, you'll piss off someone, and if they complain you can get into trouble. It helps if you live someplace where the neighbors aren't too close. If you keep the power low and the signal from spreading to where anyone else will care or notice, then you can use whatever frequency you can manage to create a transmitter for.

Eventually you can try around 27 MHz. It's been a while since I looked at the regulations. That is where the old CB bands were. You could buy "walkie talkies" for those bands that you could use without a license at all. The range on those was usually under a mile, but most didn't put out as much power as they were legally allowed. Lots of rules may have changed since the last time I looked. I have no idea whether the CB bands are even still there. If I remember right, Morse was actually forbidden on those bands, as they had to be normal AM voice. But again, keep your power low, antennas small, away from where people might care, and it's very unlikely anyone will come after you.

  • \$\begingroup\$ Thanks, im pretty sure I have a Short wave reciever somewhere. So its just an oscilator, and amplifier? \$\endgroup\$
    – skyler
    Apr 5, 2013 at 2:03
  • \$\begingroup\$ You won't receive tones, unless the receiver has a BFO for CW/SSB reception. \$\endgroup\$ Apr 5, 2013 at 10:54

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