Picture of Build a computer controlled radio transmitter
This will allow you to send morse code through radio waves to another computer. This could be used as a sort of chat program.
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Step 1: Gather Supplies

Picture of Gather Supplies
You will need very few supplies:

-A crystal oscillator (will talk about which kind in the next step)
-A 9 pin serial jack (D-SUB9)
-A little bit of wire
-Something to use as an antenna
-A radio
-A male to male audio jack (unless you know morse code)

Step 2: Which Oscillator?

Picture of Which Oscillator?
To determine what kind of oscillator you want you will need to know what kind of radio you have.

Regular AM/FM radio - We will be using only the AM part. The numbers on the dial are frequencies in KHz. Most oscillators are marked in MHz. You will probally want something in the .3MHz(300KHz)-1.5MHz(1500KHz) range.

Shortwave radio - Go with whatever frequency your SW radio can play. My radio has 3 bands. One is a KC (KHz or AM) band and the others are MC (MHz). I use a 20MHz oscillator.

Step 3: Wire some stuff up

Picture of Wire some stuff up
You will need to solder a wire onto pin 4 of the serial jack. This one should be red to make it easier to work with later but not nessesary.

You will also need to solder a (black) wire to pin 5 of the serial jack.

Step 4: Wire up the oscillator

Picture of Wire up the oscillator
Take the red wire (from pin 4) and connect it to the pin directly above the black dot on the oscillator. Next, take the black wire (from pin 5) and connect it to the pin to the right of the black dot.

Step 5: Add antenna

Picture of Add antenna
Now add an antenna to the pin opposite the black dot. You can use pretty much any insulated wire as an antenna, just as long as it isn't too thick. I used a 25 foot telephone wire.
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Hey there! Wondering how different this would be to use a usb cable instead of the serial jack.

Wondering if tablets with microusb cables might work as well? Would be cool to make your own wifi tech. I don't think it'd be much of a leap to code full html into morse code, so you could even have browser to browser kinda fun.

A USB connection would require conversion to a connection that can be digitally switched.. (On/Off).. the Serial port is a good idea, but I'm only questioning the choice of connection.. DTR usually swings from at worse -15 to +15V (As does ALL signals for the RS-232C Standard), though most now are within the -5V to +5V range.. Not sure how the oscillator would handle the -5V swing. (yes, it does go negative, turning the GND connection into the + voltage.) Doing so could harm the oscillator's internal circuitry.

Aye, a little over my head but thanks for the reply.

What do you mean by a convert to a connection that can be digitally switched? Are you saying that there needs to be an intermediary between the oscillator and the computer? Is this a single component or a whole circuit that's needed?

Could you use a diode to make sure the power stays in one direction, keeping the ground negative? Does this swing voltage only apply to the serial jack or would this also apply to the USB connection?


3 DATA + (is this similar to data 4 DATA OUT on the serial jack?)

Sorry for so many more questions! Thanks for replying tho!

Here is what he means:

An rs232 serial port has a two voltages: -14v (low) and +10ish volts (high). That is where the -15v and +15v is from. If you use the serial port to activate the gizmo, you are feeding -14v for the ground, and +10ish for the power, which is 24ish volts, which is way to high for this oscillator (it is probably 5v).

The circuit needs (should? maybe should?) be built using "ttl" level signals (0v to 5v).

An example of the "converter" that could be used is the "maxim 232cpe", which converts the -14v to +5v and the +10ish volts to 0v. This is called "reverse ttl" but works out pretty well most of the time, only in reverse.

USB is 0v and +5v, and so would likely work "better" for this circuit, as it is sort of ttl-ish to begin with.

Another option is to fire the circuit of a "parallel" port (old school printer port) as those are already ttl level and have 12 output bits to play with, 3 of which are inverted.

Another option to limit the volts is to put a zener diode on each signal line, and use it to clip the voltage to a reasonable level. That way you won't overdrive the oscillator.

Thank you.

I am trying to teach myself radio electronics in my spare time and it's hard to keep all the theory relevant. I am starting to think I might try a few simpler circuits, without radio, to get my understanding of theory a little more concrete before I try too far into the radio world. Anyway, what you said seems to make sense, and that is appreciated!

Athlon8 years ago
I can't find this oscillators with 4 pins, only with 2 :S Help pls!
stoobers Athlon15 days ago

If it has 2 pins, it is a "crystal". if it has 4 pins, it is an "oscillator" or sometimes a "crystal oscillator". It it has 2 pins and is coated with brownish plastic, it is a "resonator".

buy them at click on oscillators, not crystals
bmlbytes (author)  Athlon8 years ago
Look in old computers and desolder them. They will be found on cards that control things like serial ports, ethernet jacks, modems, etc.
ya but those are usually around 40 mhz
They sell em in the catalog section of
Win7Maniac5 years ago
Great project. Is there a program like this one that will send music out the serial port like a radio broadcast? Could you use a 1.0000mHz oscillator and tune a normal radio into 1000kHz and listen to the music? Thanks Ryan

You don't send music over a serial port, as it is a digital port. You send music over an analog port, as all sound is analog.

You could add a transistor to the oscilators output and then mix in an analog signal from an mp3 player.

I have a 4 pin 1.8432 Mhz oscillator.
Question 1). Can I decrease the frequency to within the AM broadcasting range?
Question 2).When Transmitting Morse code using the application mentioned in the article, if I set it to AM Low tone will it broadcast at half the frequency of 1.8432 Mhz.

Radio Electronics

No, for a prefab oscillator, that is too much a frequency shift. You need to buy an oscillator cut to the desired frequency.

ratheesh4u22 years ago
I want to transmit a particular text, just one word continously.
Maximum range is required.
Any possibility?
Please answer...
I badly needs this

This word later I will use it to display in a receiver.

Build this:

It is a low power morse code transmitter.

You need an amateur radio license to use it.

kill_them_now10 months ago

hi guys,i have an idea..can someone
program an android app that combine SDR Touch( an apps that can receive
am transmission offline with an RTL 2832 U driver,

) with this computer controlled radio transmitter and it software?so that we can have a pocket android am transceiver!!!..

please make it free or less than 1$ for the sake of am lover :)


You don't need an ap for this.

You need an AM transmitter that plugs into your headphone port on your phone. Then you play an mp3 and it will broadcast over the transmitter.

If you want to transmit morse code, that might be a little different, as you need to turn the carrier on and off.

Also, there aren't and long, medium or shortwave frequencies that a fellow can use without an amateur radio license, so you would be limited to 100 or so feet of transmission range.

An idea I had: Have the computer output go into the mic input of a walkie talkie. Then, have the "Brother" Walkie talkie have headphone input into my friend's computer. Would this work? Also, for a different project, how could I change this program's source code to make it output on usb port instead of serial? I don't want to use an adapter; just change the source code.

It would, except... Output from the oscillator would just be a dead frequency carrier, and a little out of range for the Mic input.. You could try using an audio level oscillator in the 28Hz to 3.951Khz (Well below the Crystal Oscillator range) for the transmitter side, and a simple LM567 Tone Decoder chip tuned to pick-up on the specific tone on the receiver side.. The drawback with USB, is it is not a standard On/Off signal.. USB is constantly sending/receiving data, to whatever device it is connected to. Hence the serial port.. One suggestion, would be springing for a microcontroller like the Arduino, which uses an on-board USB to TTL-Serial converter (TTL means Transistor-transistor Logic, plain 0 to +5V, Not RS-232C -15/+15 voltages),.. But, again, it would require programming the Adruino instead of the computer.

Joshua_ag1 year ago
on the computer where should i connect that 9 pin serial jack?

Covering both of your questions, You could, but I would stick to nothing higher than the 1.8Mhz Video Oscillator.

As for the 9-Pin serial jack, the original poster is using what used to be the original standard for communicating, the RS-232C serial jack, which most modern computers don't have.. But, as fortsackville had asked recently, you could use a USB to Serial adaptor dongle. (changes a USB port into the old standard.) but, I still question the direct connection to the voltages generated. The DTR (DB9 #4, Data Terminal Ready) , RTS (DB9 #7, Request To Send) pins are signals generated by the computer to tell external devices either the computer is ready for more data or to stop, while received is being processed, or that the computer is ready to start sending. They're mostly used in digital transmitting like PSK31 as the PTT (Push To Talk) switch to key-up the transmitter. DB9 #5, is a frame/signal ground, used for return back even with the RX & TX data pins

Using a xtal oscillator in the amateur radio bands could make a very nice QRP beacon

It would make for a VERY Simple QRP transmitter! But, most oscillators are usually a fixed frequency and usually chosen outside any normal allocated radio (commercial or civilian) frequency band.. With exception of the ones that have trimmers. LOL! I wonder if anyone has done any QRP Contests with one? (DE KA1OBK)

kill_them_now10 months ago

hi guys,i have an idea..can someone program an android app that combine SDR Touch( an apps that can receive am transmission offline with an RTL 2832 U driver,

) with this computer controlled radio transmitter and it software?so that we can have a pocket android am transceiver!!!..

please make it free or less than 1$ for the sake of am lover :)


Can i use this as a Remote controller for a RC plane kinda things?

Could this be used to connect a Transmitter to a pc to use on a simulator?
i only have this one short two pin crystal from an original xbox mother board, would this work? and if not, would it be the same if i used a simple 555 oscillator circuit?
Joshua_ag1 year ago
can i use those small oscillators found on computer motherboards for making this?
bluescope935 years ago

Just a Question how do u send the Data to the Frequency Oscillator if all you are supplying to it is Power? , do you have a CW Key to turn the +9 Volts on and Off therefore creating a Morse Code Format?? , Or do u send the Audio for a Mono 3.5 or 6.5 Plug into a Radio or Computer and play a Tone or music??

Cheers and 73's
Turning on and off the oscillator via the computer's DB (De) 9 port IS keying the oscillator. It can be unmodulated - - CW mode -- or modulated. In this case the computer program handles the selection and transmission of those modes.

Turning on the Carrier Wave - and then off - to form Morse code characters, is the very definition of CW mode.

Joe, N2QOJ
would you please release the source code? i have no idea how to use various i/o ports on a system, and i dont want to sord through pages of dissasembly to find my love it if you would release the source :D
bmlbytes (author)  abamailinator3 years ago
I didn't write that program.
Could you attach a microphone instead of the serial thing to send sound? I want to send sound around my town.
This reminds me of something. Oh yeah there was this other site that has the same pics and stuff. 
just checked this out, i wonder how hard it would be to implement it with a arduino?
Oh, and uh does anyone know the legal limit of broadcasting signals from point A to point B in the Philippines? Otherwise, I'm making a pocket morse code transmitter!
martzsam4 years ago
Will this program work with windows 7?
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