Radiated Emission: Why Your USB Case Must Not Be an RF Polluter

Q: What does 40 dBµV/m mean?

It is the field strength limit measured at 3 meters, expressed in decibels relative to one microvolt per meter. Lower is quieter; staying below the line is the pass condition.

Your Charging Case Is a Tiny Radio Station. The Question Is Whether It's Legal.

Sit in an aircraft cabin with a USB charging suitcase at your feet and you're sharing the airwaves with every phone, headset, and navigation system on board. Most of them behave. Some don't.

Radiated emission testing is how we prove our cases are the well-mannered kind. And it's the test page most buyers never open — which is a mistake, because it's the page that protects the environment your product will live in.

The Direct Answer

Radiated emission testing measures how much electromagnetic noise your product broadcasts into the air. EN IEC 55014-1 caps it at 40 dBµV/m from 30-230 MHz and 47 dBµV/m from 230 MHz-1 GHz, measured at 3 meters.

In our Model 1338 report, the charging case passed with margin — the emissions from its charging circuit stayed below the limit across the whole band. A product that fails this test isn't just non-compliant. It's a small radio polluter that can degrade other electronics nearby.

Why a Charging Circuit Can Act Like a Transmitter

Every switching regulator produces noise as it chops power. That noise travels along PCB traces and cables — and cables act like antennas. That's exactly why a USB charging case can radiate. The usual suspects:

Switching regulators and their layout
USB ports and cables acting as radiating elements
Poor grounding and shield terminations
Long internal wiring routed near the shell edge

None of this means the product is broken. It means the electronics need to be designed for silence, not just for function.

The Limits, in Plain Language

Frequency band	Limit at 3 m	Detector
30 MHz – 230 MHz	40 dBµV/m	Quasi-peak
230 MHz – 1 GHz	47 dBµV/m	Quasi-peak

dBµV/m is a logarithmic measure of field strength. The numbers sound small, but every 20 dB is a factor of ten in power. Quasi-peak is a detector that weights repetitive noise the way a real radio receiver perceives it — which is why the test method matters as much as the limit.

How the Test Actually Runs

The product operates in its normal mode — for the 1338, charging function active, supplied by its power bank.
It sits on a turntable in a 3-meter semi-anechoic chamber, the room that kills reflections so measurements are honest.
A receiving antenna measures the emissions, first horizontally, then vertically — because the product radiates differently in each polarization.
The product rotates and the antenna height scans to catch the worst-case direction.
The measured level is corrected for antenna factor, cable loss, and pre-amplifier gain to get the final level, which is compared to the limit.

Our report shows the horizontal and vertical measurement data, with the final level calculated the same way on both pages: reading level plus antenna factor plus cable loss minus pre-amplifier gain.

Factory Data: Test the Real Product, Not a Convenient One

When we sent the 1338 for testing, we asked the lab to run it in the real charging mode with the actual power bank — not a lab substitute. Emissions depend on the current the circuit draws, so a test with a dummy load would have told us nothing about the product we actually ship.

What "Pass" Means

Pass means the measured emissions stayed below the limit across the whole 30 MHz-1 GHz range, in both polarizations, in the worst-case orientation. It does not mean zero emission — nothing electronic is silent. It means the noise is low enough that it won't cause problems for other equipment, and it meets the legal limit.

Why Buyers Should Ask for This Page

For EU market access, radiated emission testing is a CE requirement under the EMC Directive. For US programs, the equivalent scope is FCC Part 15, which needs its own assessment. Asking to see the emission pages and their margins tells you whether the factory tested a real configuration or a convenient one.

Frequently Asked Questions

What frequency range does radiated emission cover?

For EN IEC 55014-1 with a product clock below 108 MHz, the range is 30 MHz to 1 GHz — which is what our report covers. Products with higher clock frequencies extend to 2, 5, or 6 GHz.

What does 40 dBµV/m mean?

It's the field strength limit measured at 3 meters, expressed in decibels relative to one microvolt per meter. Lower is quieter; staying below the line is the pass condition.

Which part of a suitcase radiates?

The electronics — switching regulators, charging circuits, USB ports, and the cables connected to them. The shell is not the emitter; the circuit board and wiring are.

Can a product pass emissions but fail immunity?

Yes. The two are independent tests with independent fixes. A quiet product can still be easily disturbed, and a robust product can still be noisy. That's why both halves of EMC are tested.

Does a battery-powered product need radiated emission testing?

Yes. Battery power removes the mains tests, but radiated emission applies to any electronic product regardless of power source. The noise leaves through the air, not only through the power cord.

What margin should a good report show?

Comfortable margin is better than a squeaked pass. Our 1338 passed with margin across the band. If a report shows results hugging the limit line, ask the factory what margin they expect on production units.

About This Report

The radiated emission data in this article comes from report No. GTS2025080251E01 for our Model 1338 — measured at 3 m in a semi-anechoic chamber, horizontal and vertical polarization, 30 MHz-1 GHz, pass. We share the emission pages with buyers and, when needed, run the same discipline for FCC Part 15 programs through accredited labs. Ask for the pages at clkbusiness@clkluggage.com or WhatsApp +86-18879628221.

About the Author

Written by the CLK Manufacturing Team — 16+ years of custom luggage OEM/ODM experience from our factory in Ji'an, Jiangxi, China. Updated: 2026-08-15.