SSB + carrier is actually SSB, as algorithmically defined. We hams use SSB-SC which is SSB having suppressed carrier. When NTSC was being debated in the mid-40's, the video transmission was originally proposed to be SSB-SC to reduce the video TX power by sideband and carrier elimination, especially at VHF frequencies where it was difficult at that time to transmit at reasonable power efficiencies.
SSB-SC was dropped because it was found that the vast majority of video content (analog, of course) was heavily weighted in low frequency, requiring good fidelity down to DC. SSB-SC has no DC reference and has poor LF fidelity. SSB (with carrier) was found to also suffer poor LF performance and corresponding picture fidelity. It was from this and also the ability to easily implement AFC (automatic fine tuning control) on the receiver that a small remnant, a vestige, of the lower sideband was included in the transmitted signal. The result was a very, very expensive modulator/PA but a reduced cost television receivers with good linearity across the 4.2MHz luma bandwidth (another technical feat in 1948) and this is what both Zenith and (General) David Sarnoff wanted - cheap receivers! Lee Pedlow Systems Engineering Sony Electronics, Inc. San Diego, CA CONFIDENTIAL This email is covered by the Electronic Communications Privacy Act, 18 U.S.C. 2510-2521 and is legally privileged. This e-mail is intended only for the personal and confidential use of the individual(s) to which it is addressed and may contain confidential information. If you are not the intended recipient, you are hereby notified that you have received this document in error, and that any review, distribution, copying or disclosure is not authorized. If you have received this communication in error, please notify the sender immediately by telephone and destroy the message. -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Larry W8ER Sent: Wednesday, December 20, 2006 12:44 PM To: Reflector Flex; Jim Lux Subject: Re: [Flexradio] SSB with Carrier? 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 _______________________________________________ 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
