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.
I have attached the PDF file in the last step to this Inst'able for those without a pro membership.
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Signing UpStep 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==
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^ here is a link that will explain it
I had similar results. I was able to hear the audio throughout the AM channels
When implemented circuit , I've discovered that it work only when I touch one of its parts
Although I put an antenna, how to rectify this problem: (
Sorry
I looked around and the highest frequency I could find was up to 2 MHz. :(
You might have to do something with some LC-circuits or something along those lines.
Hope this helped!
I'd rather do something simple that works than attempt something complex that leaves me feeling like I got nothing accomplished.
that isn't to say that you shouldn't strive to do meaningful, big, important things, but i guess what i'm trying to say is that it is good to start small :)
that is just my two cents though.
take it with a grain of salt.
i think it is mono.
hope this helps!
Ryan
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.
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.
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.
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