Could you provide a link to help us find the explanation?topito2 said:
You can see the system working in the following video. The audio is in Spanish but it shows the system working.berkeman said:
Snap Circuits Manualberkeman said:
Audio signaltech99 said:
Sorry, that doesn't really help. I need a full schematic of the whole circuit, preferably with an explanation of how it works. Is that included anywhere in the documentation?topito2 said:
Only the positive peaks of the audio turn the transistor on and sink current.topito2 said:
Yoiks, so illegal to build and transmit at any reasonable power level then? Hopefully the range of that AM transmitter kit is less than 10 meters...Baluncore said:
It is a very clever implementation of a low power AM transmitter. It reminds me of tuned-output spark transmitters.berkeman said:
Interesting. I may have to simulate it to see what is going on. It's hard to believe that snapping a 2nd order LC resonator on and off won't result in out-of-band harmonics, but you might be right. The bandpass filters that I'm more familiar with in the WiFi band are much steeper than 2nd order.Baluncore said:
I do not believe it is being "snapped" on and off.berkeman said:
I'll go out on a limb here:Baluncore said:
Would a simple tank circuit really eliminate harmonics? Perhaps you mean that the actual power level would be low and that the (very short) antenna response would also be low.Baluncore said:
Not if your "snapping" is band limited in the audio range.berkeman said:
Yes, this is the point the RF emission spectrum is essentially determined by the resonant tank properties, spread out a bit by the audio AM modulation. So, good Rx or Tx circuits use narrow filters of some sort.berkeman said:
Yes, if the diode switches in response to the tank oscillation, then you'll get RF Harmonics. If the switching is fast but driven by the audio, then the HF noise will be spread out. If you look for it, I'd bet you see both effects.Baluncore said:
That's an interesting observation. I wouldn't expect that from a typical class AB amp. Perhaps from cross-over distortion? Or PSRR effects? Did you ever find out why?tech99 said:
Well, that's exactly the information I'm looking for. I'm asking if someone can explain to me how this system works since it is not explained in the documentationberkeman said:
If you want a real noddy description. The output power of a RF oscillator will depend on the 'power supply' volts. The transistor acts as both RF oscillator and AF amplifier. The peak amplitude of the RF will be proportional to the AF signal.topito2 said:
OK, so it seems two phenomena happen in the system: we have RF oscillations and AF amplication happening at the same time, which could not be explain by conventional block diagrams of AM systems. So if I use this system in a technology class for middle school students to have them to explore AM modulators and AM transmission it might better if I just use this system for them to have a practical approach to AM transmission, but not to dive in into the specifics. Would you agree?sophiecentaur said:
It's ages since I did any simple construction but there will be dozens of simple AM project circuits on the www in which the two functions are achieved with two separate transistors. If it's taken PF thirty posts to discuss what this 'smart Alec' circuit actually does then it is clearly beyond the scope of young, first-time minds. The total amount of lacking knowledge in an average science class is quite staggering so it has to be made really easy for them.topito2 said:
Thank you so much for the helpful advice.sophiecentaur said:
Thank you so much for your answer.Baluncore said:
Thank you so much for sharing. You're very kind.tech99 said:
I will take your advice. Thank you so much.DaveE said:
That is what we are here for.topito2 said:
Hmm, not having built it, I have no idea just what the output would actually look like on a scope. I suspect it may look pretty scrappy although an AM receiver could probably give some recognisable audio out.Baluncore said:
Just to share some information I found that gave me some light about the purpose of the diode:Baluncore said:
When a red LED is used for that diode, it sheds even more light on how a significantly greater voltage compliance can be available for ringing the LC tank. With an LED the 3V power supply also seems more appropriate.topito2 said:
The diode serves no useful purpose and looks to be in backwards, but no polarity of voltage is shown. There is little current limiting in the circuit, so the transistor may fail from excess current, except that the transistor has no bias. The inductor is a very poor antenna. How does it work? Poorly if at all.topito2 said:
Turn it around and this transmitter will have an output cleaner than any other in existence.StandardsGuy said:
The Project 122 Snap Circuit AM Transmitter works by converting audio signals into radio waves that can be transmitted through the air. The audio signals are first amplified and then modulated onto a carrier wave, which is then transmitted through an antenna. The receiver on the other end picks up the radio waves and converts them back into audio signals.
To build the Project 122 Snap Circuit AM Transmitter, you will need a power supply, an audio source (such as a microphone or MP3 player), a transistor, a capacitor, a resistor, an antenna, and a breadboard or circuit board to assemble the components on.
To assemble the Project 122 Snap Circuit AM Transmitter, you will need to follow the instructions provided in the kit. The components will need to be connected in a specific order and layout on the breadboard or circuit board. Make sure to double-check all connections and follow safety precautions when handling electricity.
Yes, the frequency of the Project 122 Snap Circuit AM Transmitter can be adjusted by changing the values of the components used. For example, the frequency can be increased by using a smaller capacitor or decreased by using a larger capacitor. However, it is important to note that the frequency range of the transmitter is limited and should not interfere with other radio signals.
The range of the Project 122 Snap Circuit AM Transmitter can vary depending on the environment and components used. Generally, it can transmit audio signals up to a few meters in an open space. However, this range can be extended by using a more powerful antenna or amplifier.