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.

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==

Comments

[jmay13]

Where do you get the 1/8 inch (3.5 millimeter) female audio jack.

[rtty21]

you can scavenge them from thrift stores, buy them on ebay, or go to radioshack and get ****ed in the ***.

[alex555155]

Could I use an 8 Ohm audio transformer?

[rtty21]

that sounds like it would be an improvement from my design. I see no problem integrating one into the circuit.

Ryan

[kr.baker]

A few problems....
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.

Secondly, Q1 is non-functional according to the schematic - it is acting only as a diode. There is no path from the emitter to ground, either AC or DC, thus there will be no current gain in the transistor and no real power to the antenna. There probably should be a resistor in series with the base, and an emitter resistor to ground. Even better, the antenna should present perhaps a 50 ohm load to ground. That will give much more range to this circuit.

[rtty21]

In my defense:
I made this before I knew much about radio. I basically just knew that I had to have something oscillating at a high frequency and have audio control that high-frequency. I didn't know about radio wave propagation, how to use op-amps, generate high-freq sine waves, or any of those really useful things that could help make a radio transmitter work better. I did, however, know how to make something that produced results. I couldn't find anything on my level of comprehension that illustrated how to make an AM transmitter, so I went with whatever I could come up with that at least worked.

To your credit:
You raise several good points that I completely agree with. You obviously know more about radio then I did when i made this instructable, and it looks like you even out-rank me now.

In summary:
Thank you for the comment! I always appreciate the advice and critiques when I can get them.
I may have to make a new Inst'able some time and add these changes to the circuit.

[kr.baker]

No need for defense at all... I am NOT an expert in radio. I have 30+ years design experience in analog, digital and embedded systems design, and a little bit of that experience is in HF stuff. No "radio" at all, at least not work-related.

I just approached your schematic from a "general electronics" standpoint, with the issues that I pointed out. From a modulation standpoint, it wouldn't matter if the carrier was RF or not, it still wouldn't be analog amplitude modulation - the carrier is being turned completely on or off, instead of being smoothly modulated by the audio.

The antenna issue is the same, just general electronics, the schematic shows no path to ground.

AM is not too difficult to design - you just need to figure out a method to control carrier amplitude based on the audio signal. There are MANY ways to do that. Analog multipliers, FET gain-control, etc.... FM is a different matter, but still not too difficult to transmit. AM reception is not too difficult, on a primitive level, even SSB is not TOO bad. FM is a fair bit more difficult on any level.

I wasn't trying to put you down at all, just trying to provide some constructive "criticism", if that is even the right word. I didn't want a bunch of folks expecting to build this and think that it would allow them to transmit AM with the quality of a radio station. I was also hoping that my comments might give you (and others) some incentive to explore further and continue to LEARN. Reading and building circuits is the key to furthering your knowledge. Don't rely solely on college or schooling, buy LOTS of books and study. Experiment. Don't just figure out WHAT works, figure out WHY some stuff works and why some doesn't. I've had exactly ONE course in Electronics, about three weeks in high school, and the Physics teacher taught vacuum tube theory. I filled out all my tests with solid-state equivalents.... ;-) So, he made me work, but I made him work too, because he had to research and see if my solid-state circuits really were equivalent!!!! That was FUN!

I'm not that familiar with "Instructables", but there is likely a way to send a message. Let me know if you need some ideas.

[kr.baker]

BTW, I can recommend allaboutcircuits.com for a hobby-friendly forum. I'm on there, but VERY rarely. A work colleague of mine is on there a LOT (he's a super-moderator) and there are lots of good folks there that are very knowledgeable. They WON'T do your homework for you though.... ;-)

[rtty21]

I trust you weren't trying to put me down. I really do appreciate the criticism! It can only make me more humble and intelligent.
I have edited my instructable to reflect your analysis.
I quoted you; I hope you don't mind. If you don't want me to quote you, I can remove it.

When I next take a swing at AM radio, I will definitely keep what you have said in mind.

P.S.
Thanks for the website link! I always like getting more websites packed into my electronics bookmark folder!  XD

[buppythebupo]

I am very new to electronics, and I am trying to decipher the schematic. Does the +5v and the ground go to the battery? Great post by the way! Having fun so far!

[rtty21]

yes. 5V and ground got the positive and negative terminals of your battery or power supply. :)
I'm glad you like it.
also, 256th comment! w00t!

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[lukas_tek]

i try one fm spy bug from talkingeletronics.com is very good
your is good too

[rtty21]

ok

[lukas_tek]

rtty21 the ne555 works?
if not sorry because the many questions i make for you!
if the mensage is wrong try undurstand that
i'm brazilian
i'm noooooooooooooooooooooooooob

[rtty21]

th NE555 will absolutely work.
Don't worry about asking to many questions.
People who know the answers enjoy answering XD

[lukas_tek]

i use i piece of solder like a antenna it works?
rtty21 my doesnt work i try with 5 volts,7.5 volts and 9 volts.
a try every frequency
a little amp in the audio in
nothing works!

[rtty21]

i don't know... is your radio set on AM radio?

[lukas_tek]

yes!
i will try make this again

[mattman2]

if i were to up the voltage going into the transmitter would that increase the range and quality or if i increased the audio input would it?

[rtty21]

it could. Many 555 timers can only handle voltages of up to 18 volts. only run your 555 on voltages under 18 volts!

[mattman2]

OK thanks and would you know how to modify this so it transmits in short wave

[rtty21]

I have no idea. sorry

: (

[DKdekes]

couldnt you change one of the capacitors going into the ic?

[rtty21]

i don't really know what short wave is... what is it?

[MROHM]

Just a Suggestion,,,I would run the Voltage@< 12 v.d.c. (For safety Sake)

[rtty21]

^

[DKdekes]

would adding another transistor help the range issue?

[rtty21]

probably not. If the transistor is switching a higher voltage, it may help a little bit. I tried doing this with a transistor switching 9V signal and i didn't notice any range difference.

[salexandridis]

It's me again! Can I replace the potentiometer with a normal 4.7KΩ trimmer ? Also can I supply the circuit with 9V or 3V?

[salexandridis]

First of all I would like to congratulate you for your well-designed and simple circuit.
I am considering trying to use your circuit compined with the pre-amplifier circuit below:
http://www.instructables.com/id/Pre-amp-to-electret-mic/
Lukas_tek suggest connecting the "output to next stage" to pin 4. What is your opinion on that? If the solution above is not the most appropriate, how can I get a better result using a electret microphone?
Thank you in advance,
Sotos.

[rtty21]

that seems like it would work! very interesting idea.

[XDule 97]

does the potentiometer control the frequency of the transmiter? can i plug in a microphone? What kinds of transistors can i use, which one will work the best? would a larger antena give about 5 meters? and which frequency is best to tune youre AM reciver for the best qality and range? Sorry for bad english. please answer these questions.

[mmclsikic]

Neces uspeti da preguras odredjeni domet zbog ogranicenosti snage ulaznim naponom i snagom tranzistora. Na ulazu u predajnik moras postaviti predpojacalo za mikrofon ili izvesti signal sa nekog uredjaja bez predpojacala ali mu moras podesiti ulaznu impedansu novim potenciometrom. Na izlazu mozes postaviti jos jedan trazistor (izlazni signal na bazu novog tranzistora) koji ce imati zasebno napajanje veceg napona i struje a tranzistor da bude vece snage npr 2N3055.Tada da bi jos poboljsao transmisiju moras izracunati duzinu antene u zavisnosti od talasne duzine koju emitujes i ona mora biti bar 1/4 duzine talasne duzine signala...

[rtty21]

the potentiometer does in fact control the operating frequency of the radio.
you will have you have a special type of microphone that generates electricity.
use a NPN transistor.
I plan to make an instructable about antennas
I suggest anywhere in between 600 and 800 kilohertz
P.S. you English is awesome

[beehard44]

for the microphone, you cannot directly plug it in, you need an amplifier
Search the web, there are a lot

[Saad Player]

hey man, this doesn't work...plzzz help me....I do hear weird sounds from my radio receiver and it means my circuit is working...I connected the audio+ and audio- to my female audio jack, and that female jack is connected to my MP3 player with the help of male audio cable...I've tried the circuit several times by tuning the radio while playing songs in the player bt that doesn't seem to work...I've also used a 4band radio receiver which is extremely strong receiver bt that doesnt seem 2 work 2! any help? :(

[rtty21]

you might want to consider using an op amp on the audio + and audio - inputs. I don't know a lot about them, but i know they amplify signals really nicely. google them would be my suggestion.

[Saad Player]

and some more thingzz....I've used all the correct components with the correct values except for the potentiometer which is 4.7 kilo-ohm. and plzz can u give some suggestions quickly?...it is for my science fair project in school this year and I have to submit it by the 28th of this month.

P.S- U haven't given any specifications abt the transistor...any NPN transistor will work? I have used A1015 NPN transistor

[rtty21]

your transistor should work.
you should use any potentiometer you have that is between 1k and 50k. those are my absolute min and max suggestions. if all else fails, just buy one at radioshack.

[jwotherspoon]

would any capacitors and resistors work