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#22
December 3rd 06, 06:13 AM
posted to rec.radio.shortwave
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AM recption notes.
Brenda Ann wrote: wrote in message ups.com... wrote: Michael Black wrote: I glanced at it and maybe missed something, but DSB is AM. And he certainly says it at the outset, and when he's talking about the components he's talking about 2 sidebands and a carrier. Now, "DSB" often has fallen into the meaning of "DSB with no carrier", but technically one should specifically define that there is no carrier. snip Michael Back in 1972 when I took my FFC 2nd and 1st class exams DSB was defined as the sidebands with a supressed carrier. A signal with both sidebands and the carrier was simply AM with a BW disgnator. .Now that diffintion may have slipped over the years, but from my perspective AM means both sidebands, with a carier DSB means both sidebands without the carrier, and ISB means two different sidebands with no carrier. I only have received the later, ISB, a very few times mainly on ancient STL links. No arguments from me. That was how I was taught in college, though ISB was never a topic. ISB (with carrier) has been around for a while. It was used in one of the original AM Stereo experiments. I believe it was Kahn that was using it. The only station I know of personally that used it commercially was XETRA, and it actually didn't do too badly, but you needed either a special receiver or two radios to tune the two sidebands to receive stereo. It was not a compatible system though in the sense that on a single standard AM radio, you only heard the channel (perhaps with some spillover depending on tuning) that the radio was designed to demodulate. When you study communications in a university, it tends to be pure theory rather than some specific protocol. While this seems counter-intuitive, understanding the theory means you can figure out some proprietary standard when the time comes. The only exceptions that come to mind would be something like duobinary modulation, which I think was a GTE patent, though it was treated as something generic. So getting back to ISB, it never came up, though by your description it is a matter of pulling out the sideband independently. So if you understand SSB, ISB would follow. |
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