Harmonics and Spurious Emissions – All you need to know

While using radio frequency components, one might come across various other output frequencies. You will not get any such frequencies in an ideal device, but the case is different for a real device. Real devices will always have a certain degree of additional frequencies. Most of the wireless transmitters are designed, so they emit a minimum of energies at certain frequencies. You can identify these frequencies after having a closer look at them:

  • Harmonics
  • Spurious Emissions


The frequency which occurs at the exact multiples of the input frequency is known as Harmonics. In other words, Harmonics are the undesired transmissions that are the multiples of intended transmission frequency. Almost every radio frequency transmitter produces some harmonics. This undesired transmission occurs at a lower power level than the desired transmission.

Harmonics are also considered a potential cause of radio frequency interference. Some waveforms such as square waves, sawtooth waves, and triangular waves contain a large amount of energies at harmonic frequencies.

Reasons behind Harmonics

An ill-functioning amateur radio transmitter can be a cause of high power level Harmonics. It can also affect the radio transmission of other nearby devices as well.

Harmonics can also occur because of amplifiers. As we all know, they can distort the signal waveform, or they are non-linear to some extent. A poor station design can increase the level of harmonics. So, you can reduce the interference by simply adopting a good station design.

Spurious emissions

Unlike Harmonics, Spurious emissions do not happen at the multiplication of input frequency; neither are they deliberately transmitted. Spurious emissions are unintended and often termed as issplatter. They occur as a result of intermodulation, electromagnetic interference, frequency conversion, or harmonics.

Reasons behind Spurious emissions

A device can generate spurious emissions even when it is not actively transmitting. This can happen due to high-speed signals, noisy power supplies, or other signal issues. In case the device is actively transmitting, spurious emissions can happen because of two reasons:

  • The power supply line connected to the radio contains high-frequency noise. It causes the radio’s power amplifier to generate certain frequencies.
  • The fundamental frequency is being picked up by some components on the PCB.

If a transmitter is improperly transmitting outside of the proper bandwidth or mode being used, then Spurious Emissions may occur. In such a case, the transmitter is producing splatter, which can interfere with other stations tuned to frequencies near the band.

To sum up

Harmonics and Spurious Emissions cannot be prevented, but they can be reduced up to a certain level. Any harmonic signal which is outside the transmitter’s assigned channel is considered as spurious emission. They are usually a result of poorly working devices or environmental interferences.

Following steps can be taken to control the level of interference:

  • Check the transmitter for reducing off frequency spurious emissions.
  • Ensure noisy devices and components are kept away from the antenna.
  • Avoid using an ill-functioning amateur radio transmitter.