The Real Basic Radio Transmitter — Totseans

The Real Basic Radio Transmitter

DaktologistDaktologist Global Moderator
edited August 2012 in Life
Personally this is as basic as they come and have a range of 10 miles or more. It won't do voice but will do Morse code and can be constructed from around $1.50 or less in parts.

You will need..
  • 1 crystal resonator. I used a 3.579545 MHz crystal which will work in the 80 meter ham band.
  • 1 2N3904 NPN transistor
  • 1 0.001 uF capacitor
  • 1 1K ohm resistor
  • 1 100K ohm resistor
  • 1 9 volt battery


You now need to connect everything as shown below

SWTX.jpg

Below is the pinout of a standard 2N3904 transistor for reference.

20100807060727783.gif

The antenna can be a short length of wire strung up in a tree or somewhere high and the ground wire should be connected to a copper water pipe or the ground pin of an electrical outlet (if you don't know which hole is which, leave the outlet alone and use a copper water pipe)

Tune your radio to the frequency printed on the crystal resonator and you should hear a high pitched tone or a clicking noise as you turn the circuit on and off to send Morse code. You may also find that you will need a radio capable of receiving single side band or CW as some AM radios don't work well with this circuit.

IMG_0554a.jpg

As ridiculously simple as it looks, this circuit is capable of transmitting a signal 10 miles or more and goes to show just how simple a radio transmitter can be.

Comments

  • bornkillerbornkiller Administrator In your girlfriends snatch
    edited August 2012
    I'm not really into this sorta shit unless it involves my guitar pedals, but I gotta admit. That's pretty fucking cool for something so simplistic. :cool:
  • SpinsterSpinster Regular
    edited August 2012
    So if you were to use this for Morse code, how would you send a signal ( the beep beep beep noise)
  • DaktologistDaktologist Global Moderator
    edited August 2012
    You just switch the transmitter on and off. You could connect a Morse key between one end of the battery and the transmitter circuit to do this. At the moment I'm experimenting with a modulator circuit that should allow voice to be transmitted using this circuit or parts of it.

    EDIT: Came up with a way to transmit voice from this transmitter. You will need to add an audio transformer to the circuit with its high impedance side in line with the battery input. This injects audio directly into the power supply modulating audio onto the RF carrier emitted from the circuit.

    AM%20TX%20copy.jpg

    Audio source is connected to the two terminals on the left hand side of the circuit diagram. Audio quality isn't too bad either.
  • angryonionangryonion Just some guy
    edited August 2012
    I'm a noob with this stuff but could you set a different frequency by getting a different resonator or is this set up just to work with this particular setup.
    Nice guide btw very easy to understand.
  • SpinsterSpinster Regular
    edited August 2012
    I was thinking about this yesterday, I guess its hard to send voice because the transmitter sends a signal that looks like UUUUUU But upside down lol But for voice you need to transmit a sine wave, Damn i wish i knew the proper jargon oh well Dak has figured it out anyway.
  • TheGreenDoctorTheGreenDoctor Regular
    edited August 2012
    So, could we use just any crystals, say maybe in the VHF or UHF zones?
  • DaktologistDaktologist Global Moderator
    edited August 2012
    Spinster wrote: »
    I was thinking about this yesterday, I guess its hard to send voice because the transmitter sends a signal that looks like UUUUUU But upside down lol But for voice you need to transmit a sine wave, Damn i wish i knew the proper jargon oh well Dak has figured it out anyway.

    Basically all AM transmitters emit a sine wave which is the carrier. The audio is attached or "modulated" on to that carrier. AM is a rather inefficient way of transmitting as a large percentage of the transmit power is put into generating a carrier wave while only a very small amount actually goes into transmitting anything useful, audio for example. Say for instance my shortwave transmitter puts out 50 watts of power total, 40 watts goes into generating a carrier while 10 watts goes into transmitting audio. Basically it makes it a 10 watt transmitter as the receiver discards the carrier during reception leaving the audio.

    Now take Single Side band. With a 100 watt transmitter, 100 watts goes into generating the audio signal with nothing left over as there is no need for a carrier to be transmitted alongside. However the receiver circuit is more complicated as it has to generate a carrier to mix with the incoming signal to receive anything useful but wastes no power during transmission.

    Take the two pictures below, the top is the carrier which is a sine wave with no audio attached. Below that is an AM modulated signal.

    IMG_0620.JPG

    IMG_0617.JPG

    The carrier is a nice smooth wave while the AM signal is a very "wide" wave. That extra "width" is the audio signal. When the audio signal is low, the wave will look similar to the carrier. When the audio is high, the wave will have that extra "width" on top. Hence the term "Amplitude modulation". High audio = high amplitude, low audio = low amplitude. Basically there is power being emitted when you aren't speaking and a little more is emitted when you are.

    Now the two pictures below show SSB (single side band)

    flat.JPG

    ssb.JPG

    The flat line is where the audio is low. When there is no input e.g. when you aren't speaking, there is no power being emitted from the antenna. Now the bottom picture shows the audio signal at its highest point. This is where full output power is achieved. Basically transmit power is proportional to audio input power.
    So, could we use just any crystals, say maybe in the VHF or UHF zones?

    You can but it generally takes a little playing around with capacitance values to get it to oscillate. Its pretty easy though. Low frequency say 3 MHz you would use around 0.001 uF and the higher you go, you would decrease that down to a few pF or less.
  • SpinsterSpinster Regular
    edited August 2012
    Thanks for explaining that :)
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