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Picture of Easy AM Transmitter!
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.
 
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Step 1: Parts and Prep (Small Stuff)

Picture of 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)

Picture of Parts and Prep (Bigger Stuff)
100_9359.JPG

==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!!

Picture of 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...

Picture of 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?!?

Picture of 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!

Picture of 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.

Picture of 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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dtpit1 month ago
sir, Wht s range of this transmitter
hi, what npn transistor specs did u use? thanks...
NirmalaN8 months ago

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

jensenr30 (author)  NirmalaN8 months ago
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.
SmithM8 months ago

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

jensenr30 (author)  SmithM8 months ago
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.
SmithM jensenr308 months ago

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

SmithM8 months ago

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

aljapairai8 months ago

hello there

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

ur work really appropriated ,, thanks

jensenr30 (author)  aljapairai8 months ago

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:

SparkySolar9 months ago

Lol Aliens lol

SparkySolar9 months ago

Lol Aliens lol

- 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 :)

royanirudh9911 months ago

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

EmptyH11 months ago

i built this circuit, and its not working.. help pls..

jensenr30 (author)  EmptyH11 months ago
I can't help if you don't tell me what is not working! xD

Also, make sure you have the transmitter very close to the radio receiver.
ChromeBit1 year ago

Do you have a breadboard (or a photograph from above) of your layout?

(Also, thanks for making this, explaining the physics aspect of it AND attaching a PDF for the none pro people.)

jensenr30 (author)  ChromeBit1 year ago

(also, you're very welcome for the explanations and the PDF :) )

jensenr30 (author)  ChromeBit1 year ago

I don't have any other pictures than the ones I've posted. I built this three years ago and have long since taken it apart in order to build other circuits.

As you mentioned, this IS NOT, an AM signal, an AM signal is around 1 MHZ, and a 555 is NOT EVEN CLOSE to that. It sounds like crap because it is 100% harmonics and sub harmonics that the AM radio can pick up

jensenr30 (author)  Martin Smith1 year ago

actually, depending on the model of 555 you purchase, the frequency operation can go as high as 2 MHz (well above the AM band).

I'm fairly sure Texas Instruments sells a 555 that can operate as this high of a frequency.

Of course, this doesn't solve the issue of harmonics you brought up.

To filter those it might be handy to use an LC tank circuit with a very high Q (resonance) factor.

Just spit-balling.

ChromeBit1 year ago

Do we need to have a section for 0v, and if so where?

Does the POT adjust RF Oscillation or Input/Output Audio Volume?

jensenr30 (author)  Martin Smith1 year ago
it adjusts the 555 timer's frequency (effectively changing the carrier frequency of the low-quality AM signal)

Ok thank you I am a newbie to the 555

jpawlowski1 year ago

The way the transistor is wired, it cannot function. So the only RF you're getting is from pin 3 of the chip. Indeed the circuit would work better if you just eliminated the non-functioning transistor, & attached the antenna to pin 3... the source of the RF signal (because the transistor is not functioning). You might also need to run a drain resistor of 10k from pin 3 to +5V, but I'm not sure on that. The transistor's collector is connected to +5 but there's not way to return the DC current through the transistors emitter. There should be about a 5k-10k resistor or an RF inductor from the emitter to the ground to complete the circuit & get the transistor to run (DC current must flow through the collector & emitter to function). The base of the transistor is not DC isolated for pin 3. There probably should be a .01uf capacitor between the base & pin 3. It should not be directly connected to pin 3. The transistor isn't biased either. You need about a 200k-500k biasing resistor from the collector to the base. If an inductor is used at the emitter the biasing resistor may be up to 1meg. You may also need a small drain resistor of about 10k from pin 3 to +5V but I'm not certain about that. The chip may oscillate fine without the drain resistor. With the transistor actually functioning there will be a significant boost in the RF signal & range by the signal being amplified by the transistor. Then the antenna could be connected to the emitter.

Thank you so much for the helpful advice, what is the point of a transistor radio, if the transistor doesn't work!? But could you tell me, (or anyone for that matter), the Increased range over about 10-12 Centimeters of the radio, after biasing the transistor and tying the emitter to ground with a 10K transistor? Thank you.

jensenr30 (author)  jpawlowski1 year ago

Thanks for all of the suggestions. I know this circuit isn't designed well. It is something I dreamed up three years ago when I knew a lot less about transistors and electromagnetic waves.

I can see what you mean about the transistor not doing anything. If I were to redesign this circuit I would play around a lot more with the biasing of the transistor and possibly try toying with the possibility of a ground plane to aid in the propagation of the radio waves.

However, I have far too many little projects that captivate my and steal my interest away from previous projects. I find this to be a blessing and a curse. While the newer projects that I work on tend to be very interesting to me, the nature of my creativity tends to lead me in the direction of newer projects all the time, only occasionally finishing older projects. This is the way I function.

Thanks for the comments.

karlitoboi1 year ago

sir...good day! i would like to ask a question...

a simple question...

what is the typical range of the radio receiver from the transmitter?

im talking about its radius... just to clarify...tnx sir.

jensenr30 (author)  karlitoboi1 year ago

because this is a really poorly designed radio transmitter, it can only broadcast at a range of 10 cm. It really isn't that great.
But it is quick and dirty. It needs to be right next to your receiver.

alainAlien1 year ago

olle friend have problems if the potentiometer is not going to land the leg up or if you're just using 2 legs, and if between leg 1 and 5 also stuck with earth. please Greetings

alainAlien1 year ago

olle friend have problems if the potentiometer is not going to land the leg up or if you're just using 2 legs, and if between leg 1 and 5 also stuck with earth. please Greetings

JigMcFigg1 year ago

I was wandering what formula you used to calculate the frequency range, or did you just plug parts in and see what range was there?

jensenr30 (author)  JigMcFigg1 year ago

good question! I used this online utility to calculate the frequency using different component values. http://www.csgnetwork.com/ne555timer2calc.html

great

How would you get a range between 27 Mhz and 49 Mhz ?

jensenr30 (author)  raven_squire1 year ago

Well, if you wanted a frequency somewhere in that range, chances are you would not want a 555 timer. I don't think they work that fast. You might want to look into transistor RCL oscillators like the colpitts oscillator and other similar ones.

Hope that helps!

sir when i tuch my hand with potentio meter then i heard audio
with out tuching transmiter does not work clearly................ why
and when i eject NPN and antenna from circut transmiter waking still
pleas helf me
Rajyedke1 year ago
what is voltage of power supply used here ? ?? where to connect it???
Rajyedke1 year ago
what is the voltage of power supply here..??? where to connect it ..??? sry i couldn't understand??
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