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Easy AM Transmitter!

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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)


==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!       : )
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ChromeBit1 month 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)  ChromeBit28 days ago

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

jensenr30 (author)  ChromeBit28 days 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 Smith29 days 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 month 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 month 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 month 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 month 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.

karlitoboi3 months 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 month 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 month 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 month 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

JigMcFigg5 months 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)  JigMcFigg5 months ago

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

great
raven_squire6 months ago

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

jensenr30 (author)  raven_squire6 months 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
Rajyedke8 months ago
what is voltage of power supply used here ? ?? where to connect it???
Rajyedke8 months ago
what is the voltage of power supply here..??? where to connect it ..??? sry i couldn't understand??
imaduddin9 months ago
thx guys, it's work but the sound is little loud, any suggestion?
jensenr30 (author)  imaduddin9 months ago
use a resistor in series with your speaker or turn down the volume on your radio.
bilsat9 months ago
Hello, i cant find the needed stuff for the transmitter.i dont know where to find them in my country, greece and i do not want online purchases of any form.
looney12310 months ago
Hi. this may sound stupid but isn't this an AM transmitter ? So we should put a Mic in the audio jack not an earphones right ?
jensenr30 (author)  looney12310 months ago
in general it would be used to transmit any kind of signal. I chose an audio signal from my MP3 player.
Oh i see . But can you tell me please what is exactly is the use of the 7555 chip ?
jensenr30 (author)  looney1239 months ago
the 7555 generates the base radio frequency. The audio modulates that frequency so.
emran16121 year ago
why Audio + is also connected to GND? pls help bro.
Actually transmits on a harmonic of the AM broadcast band. Very dirty square wave transmitter; but it kind of works as a simple proof of concept device.
pokooos1 year ago
For those who are asking for the npn transistor, use a 2n2222 transistor (because it's a RF transistor). it works good.
simonyu1 year ago
how do u use a breadboard?
jensenr30 (author)  simonyu1 year ago
http://bit.ly/15aQYob
^ here is a link that will explain it
simonyu1 year ago
can ordinary Apple earphones fit into the female jack?
jensenr30 (author)  simonyu1 year ago
yes. they are 1/8 inch audio jacks so they should work just fine.
-max-1 year ago
I have built one of these from my own design! it used the 555 chip and the input for audio was in between pin 3 and an inductor. only problem was range and saturation (I heard the music across all stations, especially the ones with the right harmonics.)
jensenr30 (author)  -max-1 year ago
interesting.
I had similar results. I was able to hear the audio throughout the AM channels
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