Stereo Amplitude Modulation

Cool, but how do you demodulate this?

But before you demodulate the signal, you have to go on an antenna and see how the signal looks like.

http://everycircuit.com/circuit/5889364914864128

And we can see, this signal, as @thebugger invented it, can not be transmitted, cuz there is DC voltage which you can not carry over air.

Ugh. Apparently you still haven’t realized why this won’t work! Let’s assume for a moment that an antenna can transmit perfectly for all frequencies. The receiver will still have a bandpass filter at the antenna the narrow down what the antenna receives to just the narrow frequency range of let’s say 500kHz +- 20kHz. Now, put a band pass filter on the output and see what it looks like after that. You could even make it 500kHz +- 600kHz, it won’t matter, all that low frequency <20kHz signal present in the output gets removed and the two signals are combined completely removing any possibility for stereo AM. You completely misunderstand the concept of “sideband”. Let’s saw you looked at a 500kHz AM signal in a frequency chart (not sure what it’s called). You will see a spike in the middle at 500kHz representing the carrier. You will also see two regions to the left and right that represent the lower and upper sidebands. If you remove one sideband, then you get SSB (single sideband) AM. If you remove in the spike at the middle, the carrier, the you get suppressed carrier SSB AM. What that looks like for say, a constant frequency signal at 20kHz, then you will see a 520kHz (or 480kHz, depending on which sideband is being transmitted) signal and that’s it. With you’re concept of sideband, if you had SSB AM with full carrier, then it would look like you’re AM signal passed through a diode on it’s way to the antenna cutting away the positive (or negative) half of the signal. That will add tons of harmonics while still transmitting as regular AM with extra weaker transmissions at every 500kHz above the main transmission (1MHz, 1.5MHz, 2MHz, etc.). By the way, all I that stuff I said about how single sideband stuff actually works is backed up by wikipedia. Also, all the Khan (Kahn?) Hazeltine (is that how it’s spelled?) system is is just two single sideband transmitters transmitting the two sidebands, one sideband per transmitter, so that you get two signals in the space taken up by one AM transmission. Does this make any sense or are you just as stubborn as ever, @thebugger?

Whoops. I said “500kHz +- 600kHz”. I meant 500kHz +- 100kHz.

I made a SSB suppressed carrier transmitter (search: SSB Modulator). All you have to do to make it a stereo AM transmitter is to take two of that transmitter (with one set to transmit the lower sideband and the other set to transmit the upper sideband) and combine their outputs with each other and the carrier with three resistors (or a summing amplifier if you want to amplify the signal), and you have a stereo AM transmitter. If you hook up the same input signal to both transmitters then you get regular AM.

Are you going to respond or are you going to just ignore me?

Isnt it a nice demonstration of being stubborn?

You know, if you just ignore me then that’s denying proof as to why this won’t work. And proof is, well, proof. I’ve proved why this circuit won’t work and you still refuse to believe this circuit won’t work. At least I don’t remain stubborn in the face of proof if I ever do happen to be acting stubborn.

This has nothing to do with sidebands by the way. Sidebands are a time domain thing - not the upper part of the modulated wave, and the lower one. The problem is with the bandwidth. It is an international standard to compress the audio signal bandwidth for maximum efficiency of the spectrum. It's not a technical impossibility to transmit a 20kHz bandwidth on a 500kHz carrier.

What you will see in the spectrum of your AM transmission alone is the AM transmission of a single normal AM transmitter transmitting a 20kHz and 10kHz signal mixed together in addition to a 10kHz and a 20kHz signal which will be in the VLW spectrum. Those won’t transmit. What will transmit is the AM signal of a 10kHz wave mixed with a 20kHz wave. These will NOT transmit separately. And what do you mean by this not having to do with sidebands? The whole idea of the transmitter is to use the SIDEBANDS in a different way! Even if it is to make better use of the spectrum, we’ve already established that that works, assuming the transmitter works properly. What we’re still arguing about is how the transmitter is going to work and why the current one doesn’t work. Also, you say that sidebands are a time domain thing, but that doesn’t make any sense. Sidebands are a spectral thing. The upper sideband of a 500kHz transmission transmitting a 20kHz signal is 520kHz. The lower sideband would be the 480kHz signal. These together with a constant 500kHz signal is what produces the shape on an oscilloscope of a normal AM transmission. If this were a true Kahn Hazeltine system, then the spectrum of the transmission will be a 480kHz lower sideband with a 500kHz carrier with a 510kHz upper sideband. What you have transmitting here is a 480kHz + 490kHz lower sideband with a 500kHz carrier with a 510kHz+520kHz upper sideband with some low frequency 10kHz + 20kHz signals that can’t be transmitted.

All I see here is this - http://everycircuit.com/circuit/5101711680339968. I haven't said anything about spectral efficiency, nor do I care about it. I haven't even said anything about transmitting this thing. This is low level modulation, meaning it's only a driving signal. If you can't make a linear amplifier to transmit the signal the same as the input, it's not my problem :D I see two polarities having different waveforms, which if received by a receiver the same way as I see it here, and granted two envelope detectors - two signals can be demodulated on the same carrier frequency. Why involve sidebands, when I haven't mentioned anything about them.

Because sidebands are at the center of how a Kahn Hazeltine system works! And, the receiver WILL NOT get its input the same way you see it here. It will be IMPOSSIBLE to transmit it without mixing the two signals 100% because the receiver will have a band pass filter at the antenna to filter out other stations and if you put even a very broad band pass filter of 500kHz+-100kHz then the signal will still come out 100% mixed!

Sidebands are a spectral thing. That is what you refuse to understand. They are NOT a polarity thing, but a spectral thing.

There you go again with the transmitter. Where have I said anything about transmission. If you can't make it transmit it ain't my problem. The circuit here works. Two baseband signals on one carrier wave. Furthermore, you can always step up the carrier frequency in the MHz range, where a a few hundred kHz deviation is not a problem for a well designed output filter.

And yes, I made a mistake. Baseband representation does not represent the time domain, but the frequency domain

So, assuming that it can be transmitted and received properly, it will work. However, just because it works if it’s connected to a receiver optimally (like with a wire) that doesn’t mean it’ll work. It will not be able to transmit optimally, and even if it could be transmitted optimally, no portable receiver would be able to receive it properly, and because it contains 10-20kHz signals that no AM antenna can transmit it might even be affected by the terrain such that only the 10-20kHz signal is left or only the 500kHz+- signal gets through, and in the second case it will result in complete mixture of the signals. The problem with this design isn’t in the modulation or demodulation. It’s in the transmission and reception. It will be IMPOSSIBLE to properly transmit or receive it using normal transmission reception techniques.

Look, you're talking about standards here, not the technology itself. First of all, AM signals don't have to be compressed. They can be as broadband as the designer pleases. The only reason you've become accustomed to low grade AM quality is because international standards have been set to restrict the bandwidth of individual channels to given limits, making balance between acceptable quality and efficient channel allocation. Technologically speaking, you can both transmit and receive signals of any type if you can tune the antenna correctly. Here the issue becomes a balance between transmitting efficiency and bandwidth. The antenna itself is nothing else than a resonant circuit. And like any other resonant circuit an antenna has a Q factor. For receivers it can be quite poor, because a high gain amplifier can restore the losses, but in the transmitter the Q factor is a much more complicated issue. If you want bandwidth you choose low Q antenna and pump more power into it to compensate for the losses. Completely disregarding efficiency, you CAN transmit 20kHz on a 500kHz channel, and receive it without problem. Anyway I chose these frequencies only for a smoother simulation, not because a real life transmitter would use them. And if you have two conventional receivers, one disregarding one polarity and the other otherwise, you can most definitely pick up the stereo sound on a single channel. You should stop thinking so limiting. Best ideas come from outside the box thinking. Anyway I'm a fan of your presence here on the app, just expand your horizons a little

Funny buggzy, you still dont get the problem, your modulated signal would need an antenna which can transmit from DC upto 500kHz + modulation. Thats really tooooo funny. Listen, form DC upto 500kHz. And you are talking about regulations... LOL

Your antenna will be trying to transmit a 20kHz VLW signal while simultaneously trying to transmit a 500kHz signal. That’s the problem I’ve been trying to get you to understand this whole time!

Why are you involving DC. The antenna would just reject it.

That’s the problem. The antenna will reject the DC signal. Put a lowpass filter on the output to see the 20kHz and below aspects of the signal that the antenna will see as effectively DC.

Normaly thats the point in discussions were buggzy gets rude, lets see.

Or the point in the discussion where he decides to ignore us.

Right

Okay, do you know what I see on the headline? Stereo Amplitude Modulation. Do you know what I don't see? I don't see transmitters or antennas or whatever. The fact is - if you put one envelope detector to demodulate one polarity, and another - for the opposite polarity, you will have two distinct signals on the output. I'm not here to discuss regulations, or antenna inefficiency, or some technical difficulties in order to transmit the signal. Just let it sink for a second, okay :)

So then never ever use the name "Kahn Hazeltine" in this context!

Yes. Kahn Hazeltine would not be an appropriate name for this system because a real Kahn Hazeltine system would work differently, and this design is super impractical.

@thebugger, you there?

And I have never used this name :D

You have used that name in previous versions of this circuit, but that’s not what I wanted you for. Do you know what might be a normal gate capacitance for a MOSFET with a Kn of about 5mA/V^2 and an Rds of about 100ohms? @2ctiby said that if I wanted to know about gate capacitance values I should ask someone with amplifier knowledge.

No, I have used mosfets as low speed switches and haven't needed to take the gate capacitance into consideration

Ok.

Hey, I made an audio amp (class-AB, unity gain). Wanna offer your thoughts on it?

not sure if this is real but i thought stereo am was mixed with 2 carrier 90 degree to each other