Jim, It's interesting that it has found commercial use .. especially as effective as in TV. I would believe that you are talking about the video.
I have been experimenting with AM a bit. I have found that even with traditional AM, I could drop the level of the carrier a wee bit and no one has metioned anything other than it sounds great! I expect that there is a point where I would get reports of distortion but with the AM carrier level dropped to 85 percent now, that has not happened. I am using a device that purposely outputs symetrical audio because I don't want asymetrical audio affecting the results. Getting rid of one sideband would really be interesting. I do it on receive with spectacular results, especially when there is QRM present but doing it on transmit would require some code changes. Thanks for the info. --Larry W8ER ----- Original Message ----- From: "Jim Lux" <[EMAIL PROTECTED]> To: "Larry W8ER" <[EMAIL PROTECTED]>; "Reflector Flex" <FlexRadio@flex-radio.biz> Sent: Wednesday, December 20, 2006 2:18 PM Subject: Re: [Flexradio] SSB with Carrier? > At 07:37 PM 12/19/2006, Larry W8ER wrote: > >>My question is, how much additional trouble would it be to develope an >>additional mode that sends one sideband and the carrier? This would erase >>the objections of double bandwidth and yet retain the perfect demodulation >>that AM'ers love so much. Since the information in the second sideband is >>redundant, it would be a perfect solution to all of the arguments! > > This has a name, and is used for TV broadcasts. VSB (vestigial sideband). > In practice, you get "part" of the lower sideband (about 1 MHz worth). > > And, in fact, you don't need as much carrier power as in conventional AM. > All you really need is a "pilot tone" which your receiver can then lock > onto. This was part of the ACSSB (amplitude compandered SSB) strategy, > which was proposed (decades ago?) as a replacement for narrow band FM. > > > Modern digital television broadcasts (in the US) use a similar form, with > 8VSB (8 level amplitude encoding) and a slight imbalance to produce a > pilot that can be used to acquire the signal and help train the adaptive > equalizer. If you look at a DTV signal on a spectrum analyzer, it looks > like a nice flat plateau with a little bump sticking up towards the LF > end. > > > In deep space comm, we use various forms of PSK with residual carrier to > allow acquisition and tracking, as well. While these are constant > envelope modulations, the idea is the same, give up some of the power that > is used for carrying information bits to transmit a phase/frequency > reference to make the receiver's job easier. > > > > James Lux, P.E. > Spacecraft Radio Frequency Subsystems Group > Flight Communications Systems Section > Jet Propulsion Laboratory, Mail Stop 161-213 > 4800 Oak Grove Drive > Pasadena CA 91109 > tel: (818)354-2075 > fax: (818)393-6875 > > _______________________________________________ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ FlexRadio Homepage: http://www.flex-radio.com
