150 kHz
Understanding the 150 kHz Boundary
If you build an electronic device (like a laptop charger or an LED lightbulb) and want to sell it legally, it must pass strict FCC or CE electromagnetic noise tests. The most critical test—Conducted Emissions—starts looking for noise at exactly 150 kHz.
The War on Power Supplies
Modern electronics do not use heavy, iron-core transformers. They use Switch-Mode Power Supplies (SMPS). An SMPS violently chops the 120V AC wall power on and off thousands of times a second to step the voltage down. This violent chopping generates massive amounts of electrical noise (harmonics).
- If an engineer doesn't install a heavy, expensive "X-Capacitor" filter inside the power supply, this noise will travel backward, out of the wall plug, and infect the entire electrical grid of the house.
- Because the fundamental chopping frequency of many power supplies is around 50 kHz to 100 kHz, the resulting harmonic noise spikes violently upward into the radio spectrum.
- Regulatory bodies (like CISPR 22 and FCC Part 15) declared that 150 kHz is the hard boundary. If your power supply vomits noise higher than 150 kHz back into the wall, it is illegal to sell, because it will destroy the AM radio band.
The Longwave AM Broadcast Band
While the United States uses the Medium Wave (540–1700 kHz) band for AM radio, Europe and Russia heavily utilize the Longwave (LW) band, which starts at exactly 153 kHz.
| The Physics | The Longwave Reality |
|---|---|
| The Wavelength | At 150 kHz, the wave is 2,000 meters long (1.2 miles). To efficiently transmit this wave, the broadcasting antenna must be a massive steel tower hundreds of feet tall. |
| Ground Wave Propagation | Because the wave is so massive, it hugs the curvature of the Earth. A single 150 kHz Longwave AM transmitter in Germany can provide flawless, static-free coverage to entire neighboring countries, regardless of mountains or forests. |
| The Noise Threat | Because the European Longwave band sits exactly at 153 kHz, it is constantly under attack by cheap, illegal Chinese power supplies bleeding SMPS noise into the 150 kHz spectrum, turning the AM radio signal into a wall of static. |
Key Equations
λ = 2000 m
Lower edge of CISPR CE measurement range
LISN response:
50 μH || 50 Ω: passes 150 kHz+ to receiver
EMC standards start:
CISPR 11/32: 150 kHz lower limit
IEC 61000-4-6: 150 kHz lower limit
Comparison
| Standard | 150 kHz role | Upper limit | Measurement | Notes |
|---|---|---|---|---|
| CISPR 32 CE | Lower limit | 30 MHz | LISN+receiver | IT equipment |
| CISPR 11 CE | Lower limit | 30 MHz | LISN | Industrial |
| IEC 61000-4-6 | Lower limit | 80 MHz | CDN injection | Immunity |
| MIL CE102 | 10 kHz start | 10 MHz | LISN | Military (wider) |
| CISPR 25 CE | Lower limit | 108 MHz | LISN | Automotive |
Frequently Asked Questions
Can 150 kHz penetrate water?
Yes. Because the wavelength is so incredibly massive (2 kilometers), it easily penetrates the ocean surface. The military uses frequencies in this region (and even lower VLF bands) to send encrypted, low-bandwidth text messages to nuclear submarines submerged hundreds of feet underwater.
Why do EMI tests stop at 30 MHz?
For Conducted Emissions (noise traveling backward through the physical power cord), regulatory testing is strictly enforced between 150 kHz and 30 MHz. Above 30 MHz, the physical power cord acts as an antenna, meaning the noise radiates into the air rather than traveling down the wire. Therefore, above 30 MHz, the testing shifts from 'Conducted' to 'Radiated' emissions testing in an anechoic chamber.
Is 150 kHz used in RFID?
Yes, it sits at the very top edge of the Low Frequency (LF) RFID band (typically 125 kHz to 134 kHz). Some specialized industrial tracking tags and animal implants use frequencies near 150 kHz to communicate via magnetic near-field induction.