Easy AM Transmitter!

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!       : )

Comments

[simonyu]

how do u use a breadboard?

[jensenr30]

http://bit.ly/15aQYob
^ here is a link that will explain it

[edz29]

Sir.. i want to try your circuit.. i have one question, what type/name of NPN transistor did you used??

[edz29]

Sir.. i want to try your circuit.. i have one question, what type/name of NPN transistor did you used??

[macgyver4477]

I confused is the chip number 7555 or is it a normal 555 timer chip?The only chip that I could find with the number 7555 was a 14 pin chip called LM7555?

[jensenr30]

its a 555. I'm calling it a 7555 because that is what it says on the chip i was using. it really doesn't matter if it is a 7555 or a LM555 or what. they all work. they should all have the same pins too.

hope this helps!

[blinkyblinky]

The 7555 can handle 18 volts max and about 2 volts minimum. The 555 timer itself can handle between 5 and 15 volts. These are both guaranteed voltages. If you go or above or below either one the timer may not operate properly.

[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.

[jensenr30]

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.... ;-)

[jensenr30]

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

[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?

[jensenr30]

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

[jensenr30]

I have no idea. sorry

: (

[DKdekes]

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

[jensenr30]

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)

[jensenr30]

^

[DKdekes]

would adding another transistor help the range issue?

[jensenr30]

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.

[mattman2]

very true

[alienjoe123]

how do I figure out what all the symbols mean?

[jensenr30]

are you new to the electronic hobbyist game?

-everything labeled with an "R" is a resistor.
-the thing labeled "P1" is a potentiometer.
-everything labeled with a "C" is a capacitor.
-the thing labeled "Q" is an NPN transistor

[robot1398]

actually p1 means preset 1 vr stands for a pot or variable resistor

[jensenr30]

That depends on who makes the schematic. there are industry standards, but overall people should just know what the graphical representation of a pot looks like.

[mattman2]

very true

[walidj]

what is the range of propagation in this circuit ? can it be increased by increasing the frequency ?

[jensenr30]

I believe its around 3-6 inches of range. i don't know if it can be increased by increasing the frequency

[mattman2]

actually in a short wave transmitter (pretty sure it goes for am and FM definitely for FM) you have to decrease the the frequency to increase the range

[rick6213]

can you please make a better schematic this one is hard to read, without that you made a great instructable! Thumbs UP

[slimplynth]

I like it! (thumbs up)

Doesn't a breadboard cause havoc when dealing with radio signals.. has anyone made a PCB and noticed an increase in range?

[jensenr30]

I am planning on making a PCB out of this radio after some more tinkering with the design... I'll add what I find to this instructable!

[slimplynth]

at 2 - 3ft there are still applications... range is always the first question but a restricted one could also be a good design feature too.

[7654321]

Especially since I'm pretty sure broadcasting AM is illegal without some kind of license

[jensenr30]

You are definitely correct!
I would hate to interrupt my neighbor's Glen Beck AM broadcast! lol, jk.

[clone4crw]

is there a connection between C1, C2, and pin 1? It's kinda hard to tell in the schematic.

[jensenr30]

Yes. C1, C2, C3, 555 pin 1, Audio-, and GND are all connected. The schematic program I used (ExpressPCB) is a mediocre Schematic program. If you are looking for a free Schematic with much to offer, try out CadSoft!!

http://www.cadsoft.de/download.htm

[Gedo479]

i am going to make it on a pcb what changes should i make to achieve same results??