What is the generation of Single Sideband?

Answer 1

It is the separation of the inverted bands of signals which are formed when an audio signal is mixed with a carrier. This was once thought to be Amplitude Modulation but in fact results in the original carrier plus 2 bands of signals translated from audio to Radio Freq. when they were mixed. They lie on either side of the carrier freq, with the lows adjacent to the carrier and heading away in both directions, LF or HF from carrier frequency to higher tones. For Single Side Band (SSB) use, the carrier is suppressed at generation, as far as is possible, by the use of a balanced modulator in order not to be present in the final signal, in order not to radiate. The side-band chosen for suppression is then attenuated by various methods, modern systems using a crystal filter no wider than the audio band width required for the purpose in hand. It can also be achieved by phasing in the generation stage. Speech is often tailored to as low as 1.8 khz band width, 2.4 khz at the most, for comms. purposes. The advantages of this system over the original double side-band plus carrier, erroneously named AMPLITUDE modulation, are many. Economies of :- Spectrum occupation: Although inverted, both side-bands contain identical information. We really don't need to send it twice in order to reproduce the original sound at the other end. Saves valuable space in the spectrum. Narrow Receive filters will get rid of the next-door neighbours when the system takes advantage and packs more stations into the newly available space. Power: The suppression of the unnecessary side-band reduces the power used and /or the power handling requirements of the device needed to generate the transmitted signal. Alternatively the saved power can be devoted to the wanted side-band, thus increasing the signal at the far end. Similarly, suppressing the carrier will save even higher levels of power, with all the same benefits. The carrier is crucial in the final signal but very easy to re-insert at the receiver end for microscopic amounts of power, ironically in a similar circuit to that which suppressed it in the first. Yet another significant power saving is the removal of the need for a high power audio amplifier used to modulate (mix really) the audio onto the transmitter at very high levels. With the high level "modulation" audio power of 50% of the transmitter power is needed. A 1kW transmitter needs 500 watts of audio whereas done in the early stages of the transmiiter, it needs micro-watts. Outcome: Either lower power consumed or more "talk power" (with the associated increase in signal strength at the far end) for a given amount of power. The original power level had to include 3 sets of signals..Two sidebands, only one of which is needed and an enormous carrier, which isn't needed at all. This shows that it wasn't a carrier after all. How you know that the carrier is on the correct frequency, as you tune your receiver? The other fellow stops sounding like Donald Duck, when you get it right.............easy!