We still enjoy the single sideband era for voice communication in amateur radio. And yes, when not properly tuned, it still can sound like Donald Duck. 

The single sideband era began in 1915, when the idea was first patented. Shortly after World War II, SSB modulation became popular with amateur and commercial use. Today, it holds its own on the ham bands as the premier form of voice communication.

Amplitude modulation ruled the first fifty years of radio telephony. To create an AM signal, you just add audio to a radio carrier wave. The result of this mixture is a radio signal with audio on each side. When you listen to your local AM band, you are hearing stations with a carrier of say 10,000 watts at the center frequency, with audio spreading out above and below. So, if my local station CHQR (770 kHz) is programming an audio channel 5 kHz wide, its radio signal will cover from 765 to 775 kHz. And, at 100% modulation, each audio sideband will carry 2500 watts and the carrier 10,000 watts of power. Since AM broadcasters have a total bandwidth of 10 kHz, this explains why their channels are spaced this distance apart.

AM is not very efficient for several reasons. First, two thirds of the power goes into the center carrier wave. The carrier contains no information. It just goes along for the ride. Second, each sideband carries the same information, so one is redundant. Third, when modulation is less than 100%, the amount of power going into each sideband drops, resulting in even less efficiency.

If you are interested, here is a more detailed technical explanation. Also, you might want to take a look at this video explanation from W6LG.

Single Sideband Era – More Bang for Buck

If you have been following the numbers, did you spot that two-thirds of the power is wasted in a carrier wave that contains no information? Did you also spot that 16.7% of the power is wasted in a redundant sideband?

As technology improved, radio engineers learned how to create an AM signal, and then filter out the carrier and one of the sidebands. This left all of the power going into one sideband. Since you need a carrier to demodulate the audio sideband, a carrier is simply added back in at the receiver end of things. This requires stable frequency oscillators. As they developed, so did the use of SSB.

SSB brings two major benefits. First, at least four times the power is available for transmitting intelligence. Second, three SSB signals can fit inside the spectrum space used for one AM signal.

Now, the downside of SSB is that signals are harder to tune. With AM signals, anywhere in the bandwidth will produce intelligent sound. With SSB, you need to tune exactly to the edge of the audio baseband. Otherwise, you will shift the audio pitch and everything will sound like Donald Duck.