What is the harmonic generator in an AM transmitter?

Harmonic Generator in an AM Transmitter

The harmonic generator, also known as the frequency multiplier stage, in an AM (Amplitude Modulation) transmitter plays a crucial role in the generation of the required transmission frequency. In essence, this stage is responsible for increasing the frequency of the initial oscillator signal to a higher value, suitable for radio frequency (RF) transmission.

Function and Importance

The harmonic generator functions by generating harmonics of the input frequency, which are integral multiples of the original frequency, and then selecting the desired harmonic frequency for transmission. This is achieved through nonlinear devices or circuits, such as diodes and transistors, that distort the input signal, thereby creating a series of harmonics. Among these, a specific harmonic is chosen — usually by tuning circuits or filters — which will be the carrier frequency for the AM transmission.


The process involves several steps:

  • The base oscillator generates a low-frequency signal that serves as the starting point.
  • Nonlinear elements within the harmonic generator produce a spectrum of harmonics based on the input frequency.
  • A filter or tuned circuit selects the desired harmonic frequency to be amplified for transmission.
  • This selected frequency is then modulated with the information signal in the modulator stage, following which it goes through further amplification before being transmitted.

Benefits and Challenges

The use of a harmonic generator allows for flexibility in choosing transmission frequencies and can significantly reduce the size and complexity of the oscillator circuitry required for generating high-frequencies directly. However, the approach also presents challenges such as potential signal distortion and the need for accurate filtering to isolate the desired harmonic frequency without affecting the signal integrity.


In summary, the harmonic generator is a foundational component of an AM transmitter, facilitating the up-conversion of a base frequency to a higher, radio-frequency signal suitable for transmission. Its design and operation are critical to the transmitter's overall performance, dictating both the quality and efficiency of the transmitted signal.

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