AM SSB

Radio spectrum is globally scarce, so engineers actively cut the required transmission bandwidth in half. Single Sideband transmission strongly dominates high-frequency shortwave radio and global amateur bands.

Core Concept

Both symmetric sidebands in a DSB-SC signal strictly carry perfectly identical voice information. A sharp mechanical bandpass filter cleanly removes one complete sideband to create pure SSB.

This immediately saves exactly half the bandwidth and further reduces global transmitter power requirements. Amateur radio operators confidently run 100W SSB transmitters for clear global voice communication.

Analog phase shift networks can also directly generate SSB without expensive quartz crystal filters. A strict 90-degree audio phase shifter network completely cancels out the unwanted sideband mathematically.

Key Equations

The standard mathematical representation for a pure Upper Sideband signal involves sine and cosine terms. The equation is s(t) = 0.5 * Ac * Am * cos(2*pi*(fc+fm)*t). The total transmitted SSB power strictly equals Pt = Pc * (m^2 / 4).

Given:
Carrier power Pc = 400 W
Modulation index m = 0.5

Why this formula:
SSB transmits exactly half of the total sideband power from standard AM.

Formula:
Pt = Pc * (m^2 / 4)

Substitution:
Pt = 400 * (0.5^2 / 4)

Calculation:
Pt = 400 * (0.25 / 4)
Pt = 400 * 0.0625

Final Answer:
Total SSB Power Pt = 25 W

Exam Tip: SSB is highly susceptible to analog phase errors during the final demodulation stage. A slight phase error in the receiver local oscillator completely changes the pitch of the received audio.

Key Properties

• SSB transmission strictly halves the required radio frequency bandwidth down to just fm.
• Removing one full sideband immediately saves an additional 50 percent of the information power.
• Sharp mechanical or quartz crystal filters cleanly block the unwanted sideband before transmission.
• The Weaver method uses complex phase shifting to cancel the unwanted sideband purely mathematically.
• High-frequency amateur radio bands universally use SSB for extremely long-distance voice links.

Quick Revision

• The time domain SSB waveform envelope bears absolutely no direct resemblance to the message.
• Precise synchronous detection remains absolutely mandatory for accurately recovering complex SSB audio.
• A local oscillator frequency shift directly and audibly changes the pitch of the received signal.
• Total transmitted power equals precisely one quarter of standard AM power at full modulation.
• Filter roll-off requirements make pure SSB completely unsuitable for transmitting low-frequency video signals.
• Exam trap: applying the standard AM total power formula directly to an SSB numerical problem.