Anyone who's done FCC knows Part 15 is unavoidable for wireless communication equipment. But Part 15 has over a dozen sub‑parts – different products require different standards – choose wrong and you're testing for nothing. I've seen too many cases rejected by the FCC because the wrong standard was selected or test items were missed.
This article covers the three main Part 15 standards – 15B, 15C, and 15E – what each covers, what it tests, and where things commonly go wrong.
Before looking at specific standards, one prerequisite: FCC has two certification paths.
1.1 Unintentional radiators – e.g., ordinary computers, printers, monitors, non‑wireless power adapters – use the SDoC (Supplier's Declaration of Conformity) path – applicable standard: Part 15B. Find an FCC‑recognised lab, test, keep the report, and affix the FCC compliance statement – no FCC ID required.
1.2 Intentional radiators – e.g., Bluetooth headsets, Wi‑Fi routers, ZigBee sensors, drone video‑transmission modules – products that actively transmit wireless signals – use the FCC ID certification path – applicable standards: Part 15C or Part 15E. In addition to testing, you must go through TCB review to obtain an FCC ID.
Exception: a very small number of low‑power intentional radiators can also use SDoC – it's not 100% FCC ID.
For a Wi‑Fi laptop – the wireless portion is Part 15C – the whole product's digital‑circuit unintentional radiation is still Part 15B. Choosing 15C does not mean you can ignore 15B. If the wireless module is purchased and already has an FCC ID – the whole product can use module‑reuse – but check the module type. Full modules can be reused directly – limited modules still require extensive whole‑product RF testing – not just a 15B supplement.
2. Part 15B – What It Tests
Part 15B covers unintentional radiators – unintentional electromagnetic interference generated by digital equipment. Two core tests:
2.1 Conducted emissions – frequency range 150 kHz – 30 MHz – measuring electromagnetic noise conducted along power lines or signal lines. Limits vary by band and detector type (average, quasi‑peak). Poorly filtered switch‑mode power supplies – fail immediately – a common failure point.
2.2 Radiated emissions – frequency range 30 MHz – 1 GHz – measuring electromagnetic field strength radiated into space. 3‑metre semi‑anechoic chamber – limits by band: 30–88 MHz: 40 dBµV/m – 88–216 MHz: 43.5 dBµV/m – tightening at higher frequencies.
These tests look simple – but the real issues are in PCB layout. Poor power‑plane/ground‑plane design, high‑speed traces near board edges, inadequate grounding – radiated emissions exceed limits easily. A shielding can alone won't fix it – board‑level EMC design is the right approach.
3. Part 15C – Which Wireless Products?
Part 15C covers low‑power intentional radiators – wide frequency range, diverse product types. Bluetooth, ZigBee, Wi‑Fi 2.4G, NFC, RFID – all here. Note: wireless charging is not Part 15C. Qi wireless charging is an ISM induction‑type RF device – it falls under Part 18 – a common confusion point.
RF transmit power is core. 2.4 GHz FHSS devices: conducted power limit 30 dBm – but FCC looks at EIRP (Effective Isotropic Radiated Power) – with antenna gain, EIRP limit is 36 dBm. Many manufacturers confuse conducted power and EIRP – using 30 dBm conducted with a high‑gain antenna – EIRP exceeds the limit.
Frequency tolerance: Part 15C requires ±20 ppm. Poor crystal selection – temperature drift shifts frequency. This ±20 ppm applies to 2.4 GHz – 5 GHz and 6 GHz have their own frequency‑tolerance requirements under Part 15E – don't mix them.
Frequency‑hopping systems (FHSS) have specific rules. 2.4 GHz Bluetooth devices must have at least 75 hopping channels – dwell time per channel ≤0.4 seconds. The pseudo‑random hopping sequence requires a justification statement. Some remember "15" instead of "75" – that's a test‑path error.
Spurious emissions: harmonics and non‑harmonic spurious outside the main channel – FCC has detailed limit tables. Many products pass main‑channel power – but fail on second and third harmonics.
4. Part 15E – Which Devices?
Part 15E covers 5 GHz band wireless LAN devices – primarily Wi‑Fi 5, Wi‑Fi 6, Wi‑Fi 6E, and Wi‑Fi 7.
Power limits differ from 2.4 GHz – 5.15–5.25 GHz: 23 dBm – 5.725–5.85 GHz: 30 dBm. Multi‑band devices require separate testing for each band. Key point: concurrent multi‑band transmission must also be tested – intermodulation creates new frequencies and spurious – more likely to exceed limits – both in the standard and as a common failure point.
DFS (Dynamic Frequency Selection) is a major Part 15E‑specific requirement. 5 GHz bands are shared with weather and aviation radar – when radar signals are detected, the device must automatically vacate the channel. FCC rule: within 10 seconds of detecting radar pulses, stop transmitting on the affected channel. Note: 10 seconds is FCC – EU CE‑RED is 100 milliseconds – don't use the wrong standard.
6 GHz band: Wi‑Fi 6E and Wi‑Fi 7 devices have additional spectrum and out‑of‑band emission requirements – refer to current FCC Part 15E provisions – don't apply other regions' values.
5. 2025–2026 Changes
SAR (Specific Absorption Rate) – FCC requires SAR assessment for body‑worn devices. It's not as simple as distance <20 cm = SAR mandatory. FCC has SAR exclusion threshold formulas – low‑power devices can be exempt even at close distances. MPE and SAR are two different assessment systems – don't confuse them.
SAR limits: head and torso – 1.6 W/kg (1g average). Limbs/extremities – 4 W/kg (10g average) – often overlooked.
Electronic labelling: not new in 2025 – 47 CFR §2.935 has been effective for years – eligible products may use e‑labels instead of physical labels.
For FCC certification standards, contact BlueAsia at 13534225140 (King) or email king.guo@cblueasia.com.
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