Understanding AM/FM Radio Stations

[GENIERE]

Everyone here is right to some extent. No one it seems is old enough to remember vacuum tubes...

I’m not sure of the date but I think it was in 1949 that my friend’s dad drove us to NYC to look at the transmitting equipment, WABC I think it was, and his dad may have been a broadcast engineer.

I recall little except the huge size of a vacuum tube, in my memory it was 50 feet high, but it was probably more like 8-10 feet. Years later I realized it was a very high wattage water-cooled transmitting tube that I had seen.


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[Antiphon]

I'm a professional EE and I'm not taking sides, but I must simply state the facts.

Modulation is mathematically linear in that multiplication & addition are linear,
that is (a working definition of linearity is) a*(X+Y) = aX + aY.

In fact, you do not need a nonlinear device to perform modulation. All you need
is a device with two inputs which is capable of forming a (linear) product. A
transistor operated in its linear range (with small signals) would effect modulation without
non-linearity if one input was on the base and another was on the collector.
They make special multiplying op-amps for this purpose as well.
These are still linear devices if operated properly.

A nonlinear transfer function will result in a different type of spectral change than
a linear mixer such as in a radio receiver.

An audio mixer is an adder. A modulator is a multiplier. Both are typically linear.

Hope this helps...

Edit: BTW, an audio mixer become a modulator if you slide the volume
pots up and down really fast. But you are multiplying the volume pot signal
with the audio signal.