BasicB-003-006-002
In a single-sideband transmitter, why is the speech amplifier needed?
A
Answer
Basic radio theory
Type
A
Microphones usually have a low power output
B
The sideband filter requires a large audio signal to work
C
To match the balanced modulator's output impedance
D
To improve signal fidelity
Answer Notes
Microphones are acoustic-to-electrical transducers that convert the mechanical energy of a human voice into an alternating electrical current. However, the electrical output produced by a standard microphone is extremely small, often in the range of just a few millivolts.
A single-sideband transmitter requires a robust audio signal to properly drive the balanced modulator. The speech amplifier acts as a pre-amplifier, boosting the weak microphone signals up to a usable voltage level for the subsequent modulation stages.
While good amplifier design preserves signal fidelity, the primary and essential reason the speech amplifier is required is simply to overcome the inherently low power output of the microphone. Filters and modulators later in the chain deal with the actual RF processing.
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In a single-sideband transmitter, what does the fixed RF oscillator do?
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In a typical single-sideband transmitter, what is the purpose of the filter that follows the balanced modulator?