For wireless products exported to the US, FCC compliance is non‑negotiable. Yet even experienced engineers often confuse Part 15 and Part 2 – some treat them as two independent test standards, while others mistakenly believe Part 2 is a sub‑section of Part 15.
In reality, they are parallel, independent chapters of 47 CFR, with completely different roles. Part 15 is the specific technical rule for low‑power wireless devices and digital equipment – it defines RF metrics and test limits. Part 2 is the general radio‑equipment framework – covering equipment authorisation procedures, RF exposure, labelling rules, and certificate change management. It includes both administrative processes and general technical clauses. One governs performance metrics for specific device types; the other sets universal rules across all categories. Confusing them often leads to choosing the wrong certification path.
1.1 The Boundary Between Intentional and Unintentional Radiators
Part 15 covers two main device classes:
·Intentional radiators – devices that rely on radio signals for their function: Wi‑Fi modules, Bluetooth chips, ZigBee sensors. They must comply with sub‑parts covering transmit power, frequency tolerance, spurious emissions, and occupied bandwidth.
·Unintentional radiators – products that do not actively emit RF, but generate electromagnetic noise from digital circuits and power supplies – switching power supplies, motors, clock circuits. These fall under Part 15‑B, which tests conducted and radiated emissions – the familiar EMC items.
1.2 When to Apply 15.247 vs. 15.407
·2.4 GHz spread‑spectrum devices follow 15.247 – classic Bluetooth, Wi‑Fi 4, and Zigbee typically use this rule.
Common trap: the 15.247 requirement for a ‑10 dB bandwidth of at least 500 kHz applies only to legacy DTS (Direct Sequence Spread Spectrum) devices. Modern Wi‑Fi uses OFDM modulation and is not subject to that limit. Many labs still apply it indiscriminately, causing unnecessary retests.
·5 GHz UNII band devices follow 15.407 – Wi‑Fi 5 and Wi‑Fi 6 fall here. The band is divided into four sub‑bands: UNII‑1, UNII‑2A, UNII‑2C, and UNII‑3 – each with different power limits and spurious requirements. Devices operating in the UNII‑2 bands must support DFS (Dynamic Frequency Selection) – failure here means immediate test failure.
1.3 Correctly Understanding 15.209
Many engineers treat 15.209 as a “catch‑all” limit – but that is a misinterpretation. 15.209 primarily governs unintentional radiation limits. For intentional radiators, spurious emissions are first subject to the specific sub‑part limits plus 15.205 – do not assume that all Part 15 devices simply default to 15.209 as a baseline. Ignoring the general spurious constraints while only focusing on the band‑specific rules will get your report rejected during review – costing valuable project time.
2. Part 2 – General Administrative and Technical Rules
2.1 Equipment Authorisation Procedures
Part 2 defines the authorisation paths for various radio devices – covering FCC ID applications, Grantee Code registration, TCB responsibilities, certificate changes, and product modification assessments. Crucially: Part 2 itself does not define any RF test limits – all performance metrics come from Part 15, Part 22, and other specific sections.
2.2 SAR and MPE – RF Exposure Assessment Rules
SAR and MPE (Maximum Permissible Exposure) requirements are set out in Part 2.1091, but the actual emission limits are still from Part 15.247 / 15.407. The general principle:
·Devices used within 20 cm of the body (handheld, wearable) → SAR evaluation required.
·Fixed installations with separation >20 cm → MPE power‑density evaluation applies.
In‑vehicle head units and T‑Boxes are typically classed as fixed installations and follow MPE. However, if the terminal can be removed and used handheld, you cannot simply exempt SAR. The SAR limit is 1.6 W/kg (averaged over 1g of tissue) – stricter than the EU’s 2.0 W/kg (10g average) – so budget both time and cost for this in the project plan.
3. Key Regulatory Updates – 2025–2026
3.1 KDB 447498 – Version Timeline Clarified
KDB 447498 D01 V07 became effective on 31 March 2022 – contrary to many online articles that incorrectly date it to 2025. The new version tightens SAR exemption conditions and refines test‑configuration requirements. The industry often says “test accuracy improved by 30%” – but that is a layman’s phrase; the rule itself contains no such wording – do not quote it in formal documents.
3.2 6 GHz Wi‑Fi Band Rules Now in Effect
The 5925–7125 MHz band (Wi‑Fi 6E / 7) is now fully covered by FCC certification. Devices in this band fall into three classes – VLP, LPI, and SP. Only SP (Standard Power) access points are mandated to support AFC (Automated Frequency Coordination) – LPI and VLP low‑power devices do not require AFC. Do not add unnecessary AFC hardware to terminals that do not need it – that only increases cost and test workload.
3.3 Cyber Trust Mark – Still Voluntary
The US Cyber Trust Mark for connected devices is currently voluntary. The FCC has not made cybersecurity reviews part of mandatory FCC‑ID requirements, and there is no confirmed mandatory date in 2026. At this stage, FCC reviews do not check firmware password policies or secure‑boot mechanisms. However, the regulatory trend is toward tighter control – it is wise to build security into your design early.
3.4 HAC (Hearing Aid Compatibility) – Limited Mandatory Scope
From 14 December 2026, new handheld cellular phones must comply with HAC testing – covering both RF coupling and T‑coil coupling, with a minimum rating of M3/T3. The rule (47 CFR 20.19) applies only to handheld phones – in‑vehicle modules, tablets, and Bluetooth headsets are outside the mandatory scope. Be cautious of any agency suggesting extra tests for devices that are not covered.
4. Practical Test Details – Frequently Overlooked Points
4.1 Part 15‑B EMC – Frequency Range Confusion
-Conducted emissions: 150 kHz – 30 MHz – unchanged for years.
-Radiated emissions for unintentional radiators (Part 15‑B) do not always stop at 1 GHz:
·If the device clock is below 108 MHz → test 30 MHz – 1 GHz.
·If the clock is above 108 MHz → the upper limit extends to 2 GHz.
The “40 GHz” upper limit often cited comes from 15.33 – which applies to spurious emissions from intentional radiators – it is not part of the Part 15‑B digital‑device EMC suite. Mixing these up will lead to an incorrect test plan.
4.2 FCC ID Format and Duplicate Checking
An FCC ID consists of two parts: Grantee Code + Product Code – total length must not exceed 14 characters.
·The Grantee Code used to be 3 characters; current policy allows 4‑character GCs. The GC is assigned by the FCC; the Product Code is defined by the manufacturer.
·Duplicate checking is based on the complete model number under the same Grantee Code – if your Product Code happens to match another company’s under a different GC, that does not cause rejection.
4.3 FCC ID Label – Permanence Requirement
The FCC label must be permanently affixed to the product body. The industry commonly uses a minimum legible size of 5 mm – but note that this is a practical guideline, not a regulatory mandate. Laser engraving, in‑mould labelling, or embossing all satisfy permanence requirements – ordinary adhesive stickers are not accepted. The label should be visible without disassembling the device. For very small devices that cannot physically display the full ID, you may use an abbreviated mark on the body and show the full FCC ID via an electronic label.
5. Automotive Product Authorisation – Key Decision Points
5.1 In‑Vehicle Devices with Wireless Modules
Head units with built‑in Bluetooth or Wi‑Fi are intentional radiators by definition – they must follow the FCC‑ID (Certification) path – SDoC is not an option. Many Tier‑1 suppliers try to use SDoC to shorten timelines – that approach is invalid.
5.2 Pure Display Devices – No Wireless Module
Rear‑seat displays or in‑vehicle monitors with no RF circuitry are unintentional digital devices – they can use SDoC (Supplier’s Declaration of Conformity). No TCB review is required – the manufacturer issues its own declaration and affixes the label correctly – provided the device contains no intentional‑radiator hardware.
5.3 Reserve Interfaces – The Red Line
If a board only has reserved connectors without routed RF traces or RF power supply circuits – and no transmitting hardware – it can be assessed as an unintentional device.
However, if the PCB already has RF traces laid out – even if the RF chip is not populated – the assessment becomes more complex. You cannot automatically assume SDoC applies. The decision hinges on the board design, not just the presence of components. Many projects misjudge this early and have to restart when they get closer to submission.
6. Lab Selection – Important Note for 2025
The FCC updated its lab control rules in 2025: if a testing lab is listed on the FCC’s security‑risk restricted list, test reports from that lab will not be accepted.
Do not over‑interpret: if the lab’s supply chain includes components from the restricted list, that alone does not invalidate the report. Before choosing a lab, check its status on the official FCC website.
For FCC certification and automotive compliance, contact BlueAsia at 13534225140 (King) or king.guo@cblueasia.com.
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