Why do radio transmission harmonics occur?

In summary, an antenna resonates on other frequencies besides the wanted one when it is transmitting at high power, because the transmitter amplifier has to make some compromises in terms of the linearity. This harmonic content is usually not a problem, but can be harmful if it is radiated outside of the desired range.
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Tech2025
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What I understand about harmonics, is when something is transmitted at high power, the antenna resonates on other frequencies besides the desired one. But Why?
 
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Tech2025 said:
What I understand about harmonics, is when something is transmitted at high power, the antenna resonates on other frequencies besides the desired one. But Why?
We usually assume an antenna is linear - which is fine for a new one with no no rusty bolts.
The non linear products come from the active devices in the transmitter amplifier. For the sake of efficiency, most transmitter designs will have some compromise with regard to the linearity so there will be some inherent harmonic content.
Back to the antenna. It is unlikely that an antenna will happen to 'resonate' at an exact harmonic of the fundamental of the transmitted signal but you don't need resonance for a piece of metal to radiate. Harmonics will tend to get through if you do not filter them out somewhere along the chain. The regulations are pretty severe about out of band radiation and, in addition to limits on radiated harmonic levels, other non linear products such as the theoretically infinite sidebands of an FM signal may also be radiated.
It is worth asking you what your level of knowledge of this very nerdy topic and how deep you want to delve. :smile:
Edit: PS The basic stuff about dipoles tells you that there is a resonance when the wire is a half wavelength (approx) long. Just as with vibrating strings, you can get standing wave resonances at overtones of the basic length. At around those frequencies, the antenna will radiate 'better' in the same way that the half wave dipole does.
 
  • #3
sophiecentaur said:
We usually assume an antenna is linear - which is fine for a new one with no no rusty bolts.
The non linear products come from the active devices in the transmitter amplifier. For the sake of efficiency, most transmitter designs will have some compromise with regard to the linearity so there will be some inherent harmonic content.
Back to the antenna. It is unlikely that an antenna will happen to 'resonate' at an exact harmonic of the fundamental of the transmitted signal but you don't need resonance for a piece of metal to radiate. Harmonics will tend to get through if you do not filter them out somewhere along the chain. The regulations are pretty severe about out of band radiation and, in addition to limits on radiated harmonic levels, other non linear products such as the theoretically infinite sidebands of an FM signal may also be radiated.
It is worth asking you what your level of knowledge of this very nerdy topic and how deep you want to delve. :smile:
Thanks for the explanation, Just getting started with learning antenna theory.
 
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  • #4
Tech2025 said:
Thanks for the explanation, Just getting started with learning antenna theory.
I edited my post and added a bit.
 
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1. What are radio transmission harmonics?

Radio transmission harmonics are unwanted frequencies that occur at integer multiples of the fundamental frequency in a radio signal. They are caused by nonlinearities in the radio transmission system.

2. Why do these harmonics occur?

Harmonics occur because of nonlinearities in the radio transmission system. These nonlinearities can be caused by imperfections in the components or by external factors such as interference.

3. How do harmonics affect radio transmission?

Harmonics can cause interference with other radio signals and result in degraded signal quality. They can also cause distortion and false reception of signals, leading to errors in data transmission.

4. Can harmonics be prevented?

While it is not possible to completely prevent harmonics, they can be minimized through proper design and maintenance of radio transmission systems. This includes using quality components and shielding, as well as regularly testing and calibrating the system.

5. How are harmonics detected and measured?

Harmonics can be detected and measured using spectrum analyzers, which display the frequency components of a signal. They can also be detected using specialized filters and probes that are designed to isolate and measure specific harmonics.

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