Single-sideband amplitude modulation (SSB) — a type of AM modulation of a radio frequency signal in which only one of the symmetrical sidebands of an AM-modulated signal is transmitted: either the upper sideband (USB) or the lower sideband (LSB). The unused sideband and the unmodulated carrier (occupying 50% of the power of the AM signal) are suppressed and not transmitted. No power is wasted on the unnecessary sideband and carrier.
This results in a narrower emitted signal bandwidth and a significant increase in its effective power. Thus, by switching a radio station from AM to SSB, the communication range can be substantially increased without raising the transmitter's output power. Moreover, in voice communication mode, the SSB spectrum over time has a pulsed form only during the operator's speech. As a result, the transmitter's output stage experiences significantly less load, allowing the radiated power to be increased by 2–3 times without additional cooling measures. To achieve the same received signal level as with a double-sideband transmitter, the power of a single-sideband transmitter is only one-third of that of a double-sideband transmitter. Switching to single-sideband signals yields a power efficiency gain of 4–8 times.
The congestion of the airwaves and the limited frequency resources, especially in the HF band, require narrowing the frequency spectrum bandwidth emitted by a transceiver during conventional double-sideband AM transmission. Reducing the frequency spectrum occupied by an AM radiotelephone station helps to solve the problem of frequency allocation among radio stations, which becomes increasingly acute with the continued development of maritime transport, where other terrestrial bands are either inefficient or cannot be used.
Single-sideband amplitude modulation (SSB) is a type of amplitude modulation (AM) widely used in radio communication equipment for the efficient utilization of channel spectrum and transmitter power.
An analysis of the spectrum of an amplitude-modulated signal shows that the information about the transmitted signal is contained in each sideband. In an AM radio signal, 50% of the transmitter power is spent on transmitting the carrier frequency, which contains no information about the modulating signal. The remaining 50% is evenly split between the two sidebands, which are mirror images of each other. The carrier at frequency f? is known at the transmitting side (the transmitter tuning frequency) and carries no information about the transmitted signal. At maximum modulation depth, the power of each sideband of an AM signal does not exceed 25% of the carrier power, meaning that the majority of the power is concentrated in the carrier wave.
The idea of eliminating the carrier frequency and one of the sidebands from the emitted signal spectrum is implemented in a single-sideband transmitter (SSB Transmitter). Double-sideband transmitters are no longer used in maritime radio communication.
In addition, when multiple stations with single-sideband modulation operate at nearby frequencies, they do not cause mutual interference in the form of beat frequencies, which is typical when using AM with an unsuppressed carrier.
The disadvantages of single-sideband modulation include the greater complexity of signal generation compared to double-sideband amplitude modulation (AM). Furthermore, transmitter and receiver frequency stability requirements are higher than for AM systems.
Radio signal modulation, Types of modulation (emission class), Short radio waves, CB frequency band.