Understanding the Sources of Electrical Noise: Beyond the 50/60Hz Power Line Frequency

While 50/60Hz power line frequency is often highlighted as a significant source of electrical noise, it's important to recognize that 400Hz power also sing at twice the standard power frequency, resulting in 100/120/800Hz. The doubling of frequency is caused by the two “humps” in sine wave power, which are present in each phase, such as in three-phase power systems. These effects can multiply in multi-phase devices like multi-phase transformers or rectifiers. Partial cancellation of noise can reduce the amplitude but not the frequency.

Frequency Doubling and Its Effects

Frequency doubling occurs in both electric field voltage and magnetic field current effects wherever a mechanical result produces air movement. For instance, in most applications where alternating current is used, magnetic equipment like transformers might vibrate. However, in DC-powered devices like electric subways or streetcars, you won't hear noise from the overhead wires or third rail.

Contributors to Electrical Noise

Electrical noise is any random signal that is extraneous to the one desired. It can originate within circuitry due to the jostling of atoms. Unless at absolute zero (0°K), atoms have thermal energy, which is revealed as noise—electrons moving in a circuit and generating a signal. The level of noise is directly proportional to the temperature.

Internal and External Sources of Noise

Electrical noise can also be induced externally through electromagnetic and electrostatic fields. There is a constant "smog" of electromagnetic activity around us, generated by both man-made electrical and electronic equipment and atmospheric activity from sources like the sun, lightning, and even cosmic rays. Even poor conductors like the human body can act as a capacitor plate, transferring noise signals through electrostatic means.

Minimizing External Noise Sources

In most cases, circuit design and housing can be optimized to minimize external noise sources. However, thermal noise within components often sets a minimum limit to noise levels, making it challenging to eliminate noise entirely.

Conclusion

Electrical noise is a complex issue influenced by various factors, including power frequency and its multiples, thermal energy, and external electromagnetic interference. Understanding these sources is crucial for designing efficient and reliable electronic systems.