Re: thx for clay and julius, 'Still mathetical problem, but for AM demodulation with FIR filter"

Clay wrote:
On May 29, 5:38 pm, Jerry Avins <j...@xxxxxxxx> wrote:
Clay wrote:
... To
extract the modulation from an AM signal, you will need more than just
a filter. While bandpass filters are present in pretty much all
receivers, the filters themselves do not do the demodulation. Jerry
gave a common (in hardware for broadcast AM) method for demodulation.
There are also many other ways to demodulate AM. One of the 1st
questions is your AM single sideband, double sideband, vestigal
sidband etc?
Just a comment. When "AM" is mentioned, the plain double-sideband with
carrier is usually assumed. Generally, SSB implies suppressed carrier,
but SSSC makes that explicit.


Hello Jerry,

I recall back when I was in high school and had heard that AM was
effected by multiplication and you get an upper sideband, lower
sideband, and carrier. Of course when I looked at the standard trig
identities, I saw how the upper and lower sidebands were created, but
I couldn't see how some carrier was left over. I took me a a while to
realize that the early radio designs were unable to multiply by
negative numbers. So the modulating signal was offset so that the
whole of the signal was now positive. And this gives "standard AM."
Certainly for a long time AM referred to this offset signal - positive
number only multiplication. Although TV has long been an exception to
this rule. But the last 10 to 20 years have made more complicated
forms of AM quite practical.

Clay,

Sure they're practical. They were doable 50 years ago or more. (I once built an AM system using a balanced modulator to suppress the carrier just to demonstrate carrier phase reversal when the modulating signal went negative. Synchronous demodulation was easy because the original carrier was available.)

Has the generally assumed meaning of uncharacterized "AM" changed while I wasn't looking? Or is "regular AM" a new and necessary retronym?

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
.

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