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Chris:
I worked for AT&T, Long Lines Division, and we used SSB for just about everything that went from point A to B. Let's start with plain ole AM. Let's say we have an AM station at 1,000 kHz, or 1 mHz. This is about in the middle of the broadcast band. We have a carrier power of, say, 1000 Watts. If we place a 1 kHz tone on the carrier, we will have two sidebands, one at 1mHz + 1 kHz, or 1,001,000 hZ, and one at 1mHz - ikhz, or 999,000 hZ. We usually do this with a 500 Watt audio amplifier, with an output transformer (called a Modulation Transformer}. When the transmitter is 100% modulated, there is 1kW of carrier and 500 Watts of sidebands. This has been going on since KDKA brodacast the election returns back a looong time ago.
But: the only thing we use the carrier for once it gets to the radio is re-combining it with the sidebands to make audio, using a diode (usually), and the AVC. We don't really need the carrier to recieve audio. We can modulate the audio by using a thing called a balanced modulator, and we will have the sidebands without the carrier, which we can transmit to a listener, and if he can inject the right frequency AT THE CORRECT PHASE, he will get the audio with the same quality that it left the transmitting antenna. When I say at the correct phase, you can actually use two carriers 90 degrees out of phase and transmit two separate signals by injecting carriers 90 degrees out of phase at the reciever. This is how three colors are transmitted on a single color television carrier, with the colors being sent on a sub-carrier @ 3.5794545454545454.... mHz, with two double side band carriers modulating the color with two carriers 90 degrees apart. This is double side band.
But: all the information we need to receive the audio from our radio station is present in either sideband, therefore transmitting two identical sidebands (well, mirror images of each other) is not necessary as we can recover all of that from one sideband, and that's how Ma Bell did it, and here is how:
The first thing that happened, after your phone line came into the long distance , office and was split into transmitting and receiving directions, using a hybrid coils and balancing networks, supervision (idle or busy) using 2600 Hz., the transmitting direction was sent into a balanced modulator using copper oxide rectifiers (this was in the days before geranium and silicon), where it was mixed with one of twelve carriers of 64 to 108 kHz., making a GROUP of twelve channels of conversations (or whatever) 4kHz apart. At this point, it was still Double SideBand, or DSB. As soon as a channel was modulated, it went to a crystal filter, about the size and shape of a GT sized tube, where, in this case, the UPPER sideband was blocked, leaving the lower side band, which was nothing but audio, only insted of being 350 too 3500 Hz., it was in a, say 76 to 80 (Channel 4) kHz channel. We modulated things on top of each other that way until we had 600 channels on a microwave transmitter, or 1860 on a L-3 coaxial tube. When it got to the final office, it was demodulated down to where once more, an 80 kHz carrier was applied to a 76 to 80 kHz channel (lower side band, remember) and the original signal was recovered with amazing fidelity to the original. We also did this with the audio for radio and TV networks, using a special modulator and taking two of the twelve channels in a group for the extra bandwidth needed for the higher frequencies needed for better sound than a 4 kHz message channel, altho we did put some cheapo local radio networks on message channels for high school football, minor races, and stuff like that. Ma Bell used an old system that originated in the twenties, and didn't change much over the years, while hams were experemenitng with better ways, and you might get more up to date data from one of them.
Hope this helps, let me know if I can help any more.
Lewis
SSB is used because it is more efficient than AM. A 100% modulated AM signal has two thirds of the power in the carrier. The carrier has no information. A SSB signal has essentially no wasted power (there may be a small residual carrier).
All the information is contained in the sidebands and both of them have 100% of it, so only one sideband is needed to pass a signal.
There are two simple ways to generate SSB. You can AM modulate and filter out all except one sideband. Or you can use a double balanced (product) mixer and then get rid of one sideband. That's the math in one of the other posts.
SSB demodulation is more complicated than AM demodulation. AM demodulation is essentially rectifying and filtering the signal. SSB demodulation requires a locally generated (or recovered) carrier to be re-inserted in phase.
The audio bandwidth is often restricted to save spectrum space, but there is no fundamental reason for this.
Do a web search for "single sideband" and you'll find a wealth of information, much of it from commercial and college sites. Much better than depending on a hobby site.
In addition to ham operators, many "Utility" and Military Communications make extensive use of SSB. Years ago a number of International Broadcasters did their news and entertainment transmissions on SSB but this seems to be very infrequent anymore. As you can tell, I'm a big fan of SSB because its loaded with interesting listening - distress calls, weather information, 'numbers' stations and other curious broadcasts.
All one needs to "clarify" an SSB signal is a Beat Frequency Oscillator or "BFO" circuit. There are lots of BFO 'adaptor' schematics and kits available which can easily be connected to inexpensive shortwave radios so they can demodulate SSB signals. The BFO 'adaptor' should be able to tune both upper sideband 'USB' and lower sideband 'LSB'.
:Hello all! Can anyone clarify what exactly sideband is in ham radio? I sort of understand that there are bands or band width on each side of the carrier wave.There is this thing about removing the carrier which doesn't make sense ,how can you get rid of the carrier??Also do the side bands have a very narrow frequency response so only good for voice and not music?Thanks for info!
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