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True Oldies 106.7 is coming through my computer speakers!

littlejohn said:
And if the system is non-linear it will by definition produce an AM component, since it does not reapond linearly.
Click to expand...

I'm not out of nits yet(grin)

I don't buy that non-linear systems generate an AM component that wasn't already there.

By definition, in a linear system, the output signal amplitude is always the same multiple of the input signal amplitude.

For example, if the input signal is 1 volt, the multiple (gain) of the system is 2, the output signal is 2 volts.

If the system is linear, if you change the input signal to 5 volts, the output signal remains twice the input -- 10 volts. If you change the input signal to 0.2 volt, the output is still twice the input -- now, 0.4 volt.

By definition, a non-linear system is one in which that relationship doesn't hold. You may get 2 volts out for 1 volt in, but 15 volts out for 5 volts in and 0.3 volt out for 0.2 in. The gain changes depending on the amplitude of the input signal.

At a properly-operating FM station, the input signal amplitude does not change. ("FM" -- Frequency Modulation -- means the strength of the signal doesn't change but its frequency does.)

The input signal is 1 volt, the output is 2 volts. What happens if the system isn't linear? What happens if, if the input signal was changed to 5 volts, the output went to 15 instead of 10? It doesn't matter, because the input signal won't change to 5 volts.

_________________________________________________

Of course, the story is very different in an AM station, where nonlinearity will result in distortion. And if you have two FM signals in the same non-linear system, they will indeed mix to form FM signals on other frequencies.

But they will be FM signals, with no AM component created.
 
I remember there being an issue about people living on the south side of the metro who would hear 107.9 bleeding through their toasters and other electronic products. Is that problem still going on?
 
We are at odds over definitiion here. I consider a non-linear system as one whose gain varies with frequency as well as with amplitude, or in addition to amplitude, if you will. A circumstance whigh occurs in all reactive systems to a greater or lesser degree.

Dunno about the 107.9, but I do remember a subdivision where there were recurring complaints of WYAI intruding on a televsion channel. Only one channel, nowhere else. It was finally run down to a hyperactive line amplifier belonging to the local cable company which leaked RF badly. But, not intermod or spurs... they were backing the weather scan with the station's audio.
 
littlejohn said:
We are at odds over definitiion here. I consider a non-linear system as one whose gain varies with frequency as well as with amplitude, or in addition to amplitude, if you will. A circumstance whigh occurs in all reactive systems to a greater or lesser degree.

Dunno about the 107.9, but I do remember a subdivision where there were recurring complaints of WYAI intruding on a televsion channel. Only one channel, nowhere else. It was finally run down to a hyperactive line amplifier belonging to the local cable company which leaked RF badly. But, not intermod or spurs... they were backing the weather scan with the station's audio.
Click to expand...

Very good discussion of linearity, both sides being correct. Considered getting out my old HP-4815 vector impedance meter and making some spot measurements on my computer speakers; again, only CONSIDERED it….
 
littlejohn said:
We are at odds over definitiion here. I consider a non-linear system as one whose gain varies with frequency as well as with amplitude, or in addition to amplitude, if you will. A circumstance whigh occurs in all reactive systems to a greater or lesser degree.
Click to expand...

Yep, looks like we have more than one definition for "non-linear"!

I guess you could say my definition is of "non-linear in amplitude" -- a system being "linear in amplitude" if the amplitude gain is constant with input amplitude, regardless of whether the amplitude gain is constant with frequency.

It looks as if that definition is not universal!
 
Watt...we used to get WKDA audio in the old music dubbing room on Division Street...no surprise:
what did surprise me was getting Radio Canada on JUST the speakers (with board powered off).
Maybe your buddy Roshon was messing with things?
 
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