Switch-mode power supply interference

Switch-mode power supply interference

Frequencies	10 kHz,200 MHz
Frequency Range	10 kHz - 200 MHz
Mode	USB
Modulation	—
ACF	—
Emission Designator	—
Location	Worldwide
Short Description	Switch-mode power supplies, used in many types of electronic devices, can generate RF noise on wide frequency ranges.
I/Q Raw Recording	—
Audio Sample

Switch-mode power converters can generate RFRadio Frequency noise which is often encountered by radio hobbyists. Common sources include phone chargers, AC adaptors, computers, TVs and monitors, motor inverters and anything that contains them such as air conditioners, electric car chargers and generally most types of consumer and industrial electronics.

This kind of noise typically appears on the spectrum as peaks that are slightly unstable in frequency. Often, these peaks appear evenly spaced on a certain frequency range, and this spacing can often reveal the operating frequency of the switch-mode converter. Changes in load can change the noise characteristics, and as the converter warms up, the peaks often slowly drift in frequency. These peaks are sometimes confused with actual signals. Bandwidth and shape of these peaks can vary greatly, from less than 1 kHzKiloHertz (kHz) 10^3 Hz to tens of kHzKiloHertz (kHz) 10^3 Hz or more.

Demodulated audio from these peaks often sounds "noisy" or "dirty" and it may include mains frequency component or other tones.

Switch-mode power supply noise is often a major annoyance for amateur radio operators, shortwave listeners and other radio enthusiasts. There are different means to mitigate it, such as placing ferrite cores around power supply cables, replacing low-quality power supplies with better ones, replacing switch-mode power supplies with linear ones and shutting down unneeded equipment. Using a directional antenna can help when there is strong noise coming from a well defined direction. Certain antennas such as "miniwhip" active antennas are susceptible to conducted noise and may require special procedures to avoid excessive noise.

Producers of electronic devices are required to keep RFRadio Frequency emissions below certain limits that are set in EMCElectromagnetic compatibility - Extent to which electrical appliances can withstand each others radiated fields standards. Cheap devices may not always comply with these standards. Amateur radio and shortwave listening activities also often deal with very weak signals that may be significantly affected by devices that are fully compliant with standards.

Frequencies

Switch-mode power supply noise is often found on the HFHigh Frequency (3-30 MHz), MFMedium Frequency (300-3000 kHz), LFLow Frequency (30-300 kHz), VLFVery Low Frequency (3-30 kHz) and VHFVery High Frequency (30-300 MHz) bands. It's uncommon on UHFUltra High Frequency (300-3000 MHz) and above. HFHigh Frequency (3-30 MHz) and lower bands are often strongly affected.

Additional Images

RFRadio Frequency noise from a laptop charger that was plugged in. Spacing of the peaks is about 66 kHzKiloHertz (kHz) 10^3 Hz which is probably the operating frequency of the switch-mode converter. RFRadio Frequency noise peaks from a laptop charger drift in frequency as the charger warms up. Close-up of RFRadio Frequency noise peak drifting in frequency. Intermittent disruptions in RFRadio Frequency noise from a switch-mode AC adaptor may indicate changes in load or the operating mode of the switch-mode converter. RFRadio Frequency noise on VHFVery High Frequency (30-300 MHz) caused by a computer that was started. Spacing of the peaks is about 70 kHzKiloHertz (kHz) 10^3 Hz.