Question T7A09
From subelement T7 - T7A
What is the function of the SSB/CW-FM switch on a VHF power amplifier?
Why is this correct?
The SSB/CW-FM switch sets the amplifier for proper operation in the selected mode (B). Amplifiers must be configured differently for each mode because SSB/CW require linear amplification to preserve signal quality, while FM uses non-linear amplification for efficiency. The switch doesn't change the transmitted mode (A) — that's done at the transceiver. It doesn't alter frequency range (C) or reduce noise (D).
Memory tip
Remember that amplifiers must match their operating characteristics to the signal type they're amplifying. Linear modes like SSB require linear amplification to prevent distortion, while constant-envelope modes like FM can use more efficient non-linear amplification. The mode switch configures the internal circuitry accordingly.
Learn more
Power amplifiers have different internal operating classes optimized for different emission types. Class A or AB linear amplifiers preserve the varying amplitude characteristics essential for SSB intelligibility, while Class C amplifiers work efficiently with FM's constant envelope. VHF amplifiers commonly handle both weak-signal SSB communications and local FM repeater access, requiring this switchable capability to maintain proper emission standards while maximizing efficiency for each mode.
Think about it
Why do you think an amplifier would need different internal operating characteristics for SSB versus FM, and what would happen to an SSB signal if it were amplified using FM-optimized settings?