AM Phase Shift Oscillator

A few things to know about radio: 1, AM is amplitude modulation. The amplitude of the output depends on the voltage of the input. The signal carried within can be recovered by “riding the peaks” thereby revealing the original signal. This circuit is an example of that. 2, FM is frequency modulation. This means that the frequency of the output depends on the input voltage. The signal can be recovered by sending it through a frequency dependent filter which will make the higher frequency signal stronger/weaker than the lower frequency one essentially turning it into AM. This circuit as I currently see it is NOT an FM circuit. It is purely AM. 3, AM frequency range is from about 500kHz to 1.5MHz (1,500kHz). This circuit has a frequency of 25kHz. That means not only is it well outside the generally used range, it will be unable to carry audio of higher frequencies. 4, FM has a much higher frequency range than AM, around 100MHz (100,000kHz), so if you want this circuit to operate in either mode, it will have to have a much higher frequency in FM. One more thing: these frequency ranges are what commercial regulations say, they have nothing to do with the modulation type. You can do any modulation at any frequency range, its just that in the frequency range of 500kHz to 1.5MHz regulations say that this specific range is reserved for commercial AM broadcast (don’t ask me about the details, I don’t know them).

There are some radios that work at even lower frequencies. My car radio has reception in the LW spectrum, which is below the MW you described. Also, some military transmitters work below 100Hz using the ELF range. You'd need an entire city's power grid to act as an antenna for such a transmission, but it is still feasible.

Changing the Impedance of the Transistor by the audio changes the frequency of the Oscillator. It's mainly an AM modulator, but it does some parasitic FM.

Oh, I didn’t notice that it changes frequency slightly. I’ll look at it again.

It does indeed act as FM! This, however, makes it unsuitable for AM as it’ll wander around the spectrum rather than staying in one point meaning that it takes a larger amount of spectral space to broadcast that channel. However, this still has potential as an FM radio because the output could be amplified to clipping (so that it is at same amplitude no matter the input signal) and then passed through a filter to clean it up from bad harmonics.

@thebugger I was talking about the two ranges I know. Of course, there will be radio communication in almost all ranges where radio communication is feasible (for example, phones even go into the microwave range at GHz frequencies nowadays), but those were the only two that I knew any kinds of details about. And the only two that my car has. If your car has reception in the LW spectrum, what frequency range would that be, and what does it pick up? Because any higher frequency audio would be cut off.

@jason9, dont be to naive, the millitary dont use radios to transmit LADY GAGA