Easy AM Transmitter!




Posted in TechnologyElectronics

Introduction: Easy AM Transmitter!

About: I'm an 18 year old Electronics enthusiast. I have completed five semesters of schooling at Minnesota State University in Mankato. I'm pursuing a degree in Electrical Engineering. I like Arduino boards, C-pro...

You are going to build an AM radio transmitter AND you will be shown how it works. When you finish your radio, it will look something like mine in the picture above.

I have attached the PDF file in the last step to this Inst'able for those without a pro membership.

Step 1: Parts and Prep (Small Stuff)

==These are the small components you will need==

--Small Stuff--
- 555 timer chip
- NPN transistor
- two #103 capacitors (0.01 microfarads or 10,000 picofarads)
- #102 capacitor (0.001 microfarads or 1,000 picofarads)
- some short wires
- two 1 Kilohm resistors
- 10 Kilohm resistor
- 1/8 inch (3.5 millimeter) female audio jack (yours may have more or less than three
    wires, but it must have at least two)
- 5 Kilohm potentiometer 

==see next step for bigger components==

Step 2: Parts and Prep (Bigger Stuff)

==These are the bigger components you will need==

--Bigger Stuff--

- 1/8 inch (3.5 millimeter) male audio cable
- AM radio receiver
- Antenna. Yours doesn't have to be made out of a pop can, but the pop can works
- Breadboard

(see previous step for the small components)

Step 3: Schematic!!

                  ==Now that we have all of our components ready, lets put this together!==

                                    I suggest constructing this on a breadboard first.
                          If you don't have a breadboard, you are definitely missing out!
                                                If you have any questions... ASK!

                                                P.S. Don't forget to SUBSCRIBE!       : )

Step 4: Testing 1, 2, 3...

                                                                   ==Test your radio!==
        To test the AM radio transmitter, simply set the antenna next to your AM radio receiver (Alarm clock) tuned to approximately 600 KHz. Then play with the potentiometer until you can hear your music on your radio. The frequency generated by this devise will be anywhere from 100-480 Kilohertz if you used all the correct component values.
        If you hear weird sounds when you turn the potentiometer (and do not hear the audio signal) That means that your radio is working, but your audio signal needs to be configured. try turning the volumed of your audio signal up.

                 Not working? ASK ME!!! place a comment in the comment section below!      : )
                                                  Otherwise try these for troubleshooting:
~Is there power applied to your transmitter?
~Is the audio signal on?
~try turning the potentiometer.
~try turning up the audio signal

My antenna, power supply, and audio cable aren't  connected to the circuit in the photo above.

Step 5: How... WHY?!?

                                                    ==So how does this work??==
        The audio signal is controlling when the radio signal is being transmitted using its amplitude. this is called amplitude modulation (hence A.M. Radio) (See picture above).
However, as kr.baker pointed out in the comments,
"The audio is "modulating" the RESET pin on the 7555. This means that the signal is turning the carrier completely on or off, as opposed to linear amplitude modulation. Consequently, the audio will be distorted."
He raises a very good point that I hadn't given much or any thought to. You aren't modulating signals like they normally would be modulated. The audio quality will be greatly distorted because of this lack of having "linear amplitude modulation" - kr.baker
        for more on the subject of amplitude modulation, go HERE

                                            ==YOU AREN'T TRANSMITTING AM RADIO FREQUENCIES!!==
        You are transmitting at a low frequency that can be heard at higher AM frequencies. Lets say I transmit music at a base frequency of 300 Kilohertz (KHz) This music can be heard at the frequencies of 300 KHz, 600 KHz, 900 KHz, 1200 KHz,... (etc.) This is called harmonics.
        When the radio receiver's picks up a 300 KHz signal on a 2400 KHz band, the signal is heard only faintly. If you were to pick the very same 300 KHz signal on the 600KHz band, it would be exponentially stronger. This is why harmonics are only useful to a degree.
        for more on the subject of harmonics, go HERE I HIGHLY recommend this wikipedia page.

                             ==for some more radio information, see the next step!==

this picture shows amplitude modulation. image from http://www.ofcom.org.uk

Step 6: Improving Your Radio!

                                                            ==Modify your radio==

I want you to modify your radio and post a comment below that tells us what you did and how it worked! it's that simple! 

                 Although, I do have some suggestions:
  • Try changing R2 to a 3.3Kohm resistor.
  • Try cutting C3 out of your circuit.
  • try connecting the radio antenna to ground through a 1Kohm resistor
        So now it is your turn to teach me! what have you done to improve your radio??

Step 7: Extra Info.

        The radio transmitter we made can only transmit at frequencies from 110KHz to 480KHz. The AM radio band is from 520KHz to 1610KHz. Harmonics are essential to be able to hear audio signals transmitted from our radio transmitter.

               ==I buy almost all of my electronic components at MOUSER.com==

                                        ==If you liked this, SUBSCRIBE!==

==I'm making more instrucables just like this one!==

        I sincerely hope you don't hurt yourself while making this project! That being said, you are solely responsible for everything that happens while constructing this project. If you believe that you are not responsible for your own actions, then god help you.        : )

Step 8: =====PDF File=====



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    You deserve a medal, seriously, not many people spend the time to even begin to cover some of the physics, but also the pdf for the non pros is amazing, i made this just for fun using a cmos 555, and get about 95-150 meters of good tansmission, and about anothe 1/4 mile of bad tansmission, ill post a scematicof mine soon, but thank you for the great project

    1 reply

    Also im transmiyting at a frequency of 980 kilohertz base, and get some nasty harmonics

    Hello, I'm fairly new in the electronics world and was wondering how to read a schematic?

    1 reply

    Look online at theamazing turorials, its a good skill

    I met the same problem with you. The circuit works, but could not carried audio signal. Finally I found the solution, just inject audio signal into pin 3 which also connected with basis NPN transistor.

    sir, Wht s range of this transmitter

    hi, what npn transistor specs did u use? thanks...

    hai good day to you sir..just want ask if i want to set 550khz carrier frequency how should i set..and how to identify what capacitor value we should use to set that carrier frequency..tq

    1 reply

    First of all, you would need to make sure your model of the 555 can operate up to 550 kHz. Check your datasheet for that.

    Secondly, the easy way to calculate the values is to use this calculator: http://www.csgnetwork.com/ne555timer2calc.html

    If possible, you should always verify that your circuit is working the way you intended it to. In your case, it would be nice to use an oscilloscope to look at the output of the 555 to make sure it is working at 550 Khz.

    sir i am impress with your work. i have a challenge here. how should my transmitter circuit look like if i want to use and op am, a signal generator that will generate as low frequency as 32768Hz, a battery and a resonant anternna. waiting... thanks

    2 replies

    well, 32.768 kHz isn't a very high frequency. I would imagine you would need something to boost the frequency of that signal, such as a phase-locked loop.

    i am going to use a battery. Do you have any suggestion s in literature, i found Low power clock Oscillator 32768Hz which i think i can boost it with a 3 volts battery. i wish i know how i am going to amplify the signal and also a way to construct a fitting antenna. as for me i am trying to use a tank circuit but i don't know how to match the values of capacitor and the resistor. thanks

    in another sense, i will like to do a smilar transmitter with an op amp and a resonant antenna. can you give me any suggestion on how the circuit will look like? thanks

    hello there

    if i want to use carrier frequency about 750KHZ .. do i have any thing to change ??

    ur work really appropriated ,, thanks

    1 reply

    To change the frequency of the oscillator, you need to change the frequency-determining components. The simplest thing to change would be to replace C1 with a 4.7 nF capacitor instead of a 10 nF. This would increase the frequency by roughly a factor of two.

    Also, keep in mind the frequency limitations of your 555. Different types of 555's will have different maximum operating frequencies.

    I found a 555 from Texas Instruments that worked up to 2 MHz. That would probably suit your needs. I did a search on digikey: http://goo.gl/DWtjrb
    There are a number of 555 timers than can achieve frequencies up to 2 MHz and higher.

    Another suggestion would be to prototype it by soldering components onto a protoboard or a cobber board like so:

    copper boards:

    perf board:

    - mine melted
    - aliens asked me to turn it off
    - im in trouble with the fcc

    no seriously, thanks for that I was just looking to confirm that you can actually use a 555 in this manner :)

    Sir could u pls tell me the circuit if i dont want to transmit sound? Also could u pls tell me how do u choose the value of these components? if i want the frequency of the transmitter to be fixed at some value how do i calculate the value of the components.

    If u could provide me with some links of website regarding the same it would be highly appreciable.

    Thank u

    Anirudh Roy