RE: Here's A More Direct Source

Posted by Dave_K on December 13, 2016 at 08:11:37

In Reply to: RE: Here's A More Direct Source posted by Bromo33333 on December 12, 2016 at 14:56:33:

A bit of background info...

One method of implementing amplitude modulation is to multiply the input signal by a square wave at the carrier frequency, which can be implemented using diodes as switches. Because a square wave is just the superposition of an infinite series of cosines at the fundamental frequency of the square wave and its harmonics, the result of multiplying the square wave by the input signal is an infinite series of amplitude modulated signals. The fundamental and all of its harmonics are amplitude modulated by the input signal. Then you use a bandpass filter to select the one that matches the desired carrier frequency, usually the fundamental or third harmonic. This "switching" method of amplitude modulation is cheap and easy to implement in low level solid state circuits and is more linear than a square law modulator. So it's well suited for implementation on a chip and thus common.

When the FCC was soliciting proposals for FM stereo, two of the companies (sorry, I don't remember which) proposed transmitting sum (L+R) and difference (L-R) signals, with the sum transmitted in the 15 KHz baseband just like FM mono and the difference signal AM modulated into the channel space above that. If I remember correctly, one of the proposed implementations involved explicitly forming the difference signal and then using amplitude modulation, and the other proposal involved using a square wave to switch between the L signal and an inverted R signal. These two approaches are mathematically equivalent.

By the way, my background is originally RF as well (and computational electromagnetics). But I'm far from that now.

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Follow Ups Full Thread

Topic - AES Paper on Emotional Impact of MP3 Compression - Bromo33333 09:55:52 12/09/16 (26)

Music Is Music, and Motor Oil Is Motor Oil - geezerrocket 09:37:22 12/14/16 (1)

The 'religion' of motor oil, oil change interval, and brand. - Smelly_Socks 12:09:58 12/14/16 (0)

RE: AES Paper on Emotional Impact of MP3 Compression - fantja 14:43:01 12/12/16 (0)

Most CDs are super compressed anyway so what's the difference? - geoffkait 06:51:40 12/12/16 (0)

Here's A More Direct Source - Inmate51 10:33:05 12/09/16 (21)

RE: Here's A More Direct Source - Bromo33333 12:31:18 12/09/16 (20)

RE: Here's A More Direct Source - Todd A. 13:28:58 12/09/16 (19)

RE: Here's A More Direct Source - Bromo33333 13:56:03 12/09/16 (18)

RE: Here's A More Direct Source - JURB 09:49:58 12/10/16 (16)

RE: Here's A More Direct Source - Bromo33333 15:01:48 12/12/16 (0)

RE: Here's A More Direct Source - bwaslo 19:22:20 12/10/16 (14)

RE: Here's A More Direct Source - Dave_K 05:38:15 12/11/16 (12)

RE: Here's A More Direct Source - JURB 15:22:28 12/11/16 (2)

RE: Here's A More Direct Source - Dave_K 08:36:53 12/13/16 (0)

RE: Here's A More Direct Source - JURB 15:32:57 12/11/16 (0)

RE: Here's A More Direct Source - bwaslo 10:19:34 12/11/16 (8)

RE: Here's A More Direct Source - Bromo33333 11:49:23 12/12/16 (6)

RE: Here's A More Direct Source - bwaslo 12:17:41 12/12/16 (5)

RE: Here's A More Direct Source - Bromo33333 14:02:31 12/12/16 (4)

RE: Here's A More Direct Source - Bromo33333 14:56:33 12/12/16 (2)

RE: Here's A More Direct Source - JURB 18:23:05 12/13/16 (0)

RE: Here's A More Direct Source - Dave_K 08:11:37 12/13/16 (0)

RE: Here's A More Direct Source - bwaslo 14:17:28 12/12/16 (0)

RE: Here's A More Direct Source - Dave_K 06:11:13 12/12/16 (0)

RE: Here's A More Direct Source - JURB 04:26:34 12/11/16 (0)

RE: Here's A More Direct Source - Inmate51 08:35:55 12/10/16 (0)

Follow Ups

RE: Here's A More Direct Source - Dave_K 08:11:37 12/13/16 (0)

RE: Here's A More Direct Source

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