Radium <glucegen1@gmail.com> hath wroth:

>On Jun 30, 3:32 am, "Mike Kaliski" <michael.kali...@tesco.net> wrote:
>
>> It is not possible to modulate a carrier frequency at a frequency higher
>> than the carrier frequency.
>
>Why not?

Unfortunately, this is a good question and literally the first and
probably only good question you've asked so far. Yes, it's possible,
but you won't get the results you're expecting. See below.

>I am getting conflicting answers. Some say it's possible to modulate a
>carrier frequency at a frequency higher than the carrier frequency,
>others say it isn't.
>
>Who is right?

What does my politics have to do with anything? For what it's worth,
I'm politically somewhat left of center on most of my views.

An AM modulator is just a simple multiplier (mixer). The modulator
takes two signals, multiplies (or mixes) them together, and produces
an amplitude modulated output. For one of about 10 assorted JAVA
applets Google found that illustrate the waveforms see:
<http://cnyack.homestead.com/files/modulation/modam.htm>
Lots more at:
<http://www.educypedia.be/electronics/javamodulation.htm>

Note that a simple multiplier (mixer) doesn't care which frequency is
the carrier and which is the modulation. The two input ports are
essentially identical. The carrier is always higher in fequency than
the modulation input. If your derranged experiment somehow causes the
modulation input frequency to exceed the carrier frequency, the
multiplier produces exactly the same output as if the frequencies were
reversed. The modulation frequency becomes the carrier, and the
carrier frequency becomes the modulation input. In other words, with
AM it doesn't matter which input is the higher frequency, the output
is exactly the same.

If you happen to own some audio test equipment, you can easily
demonstrate this with two audio oscillators, a mixer of some sorts,
and an oscilloscope. Setup the equipment with two different input
frequencies and look at the output waveform. Now, swap inputs and
look again. It's the same. There's no question of which input is
modulating which other input. With AM, it's ALWAYS the high frequency
that acts as the carrier and the lower that acts as the modulation.

Now, please go back to your cave and read something on the basics of
modulation. If words confuse you, see the above JAVA applets which
will do it with pictures.


--
Jeff Liebermann jeffl@cruzio.com
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