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Publication Number: 470998 Rule Parts: 15.239 Publication Date: 06/15/2015
Keyword: 15.239, Part 15 FM transmitter

First Category: Unlicensed Service Rules and Procedures
Second Category: General Part 15 Transmitters (UnLic)

Question:   What measurement procedures should be used for compliance testing of a FM transmitter operating under Section 15.239 and designed to use a vehicle's wiring as a transmitting antenna?


ANSI C63.10-2013, clause 8 provides measurement procedures for FM transmitters designed for use in a vehicle. The standard addresses three different scenarios:

(1) Wireless transmission between the FM sources and the vehicle antenna (8.2);

(2) Injection into a vehicle?s wiring system via the cigarette light adapter (CLA) socket (8.3); and

(3) Capacitive coupling to a vehicle FM whip antenna, rooftop antenna, or embedded glass antenna (8.6).

The measurement procedures for these specific scenarios (clauses 8.2, 8.3 and 8.6) are sufficient to demonstrate compliance with the radiated emission limits in Section 15.239 and it is not necessary to also perform in-situ measurements for these types of FM transmitters.

The conducted test procedure in ANSI C63.10-2013, clause 8.5 is an acceptable alternative to the radiated emission test method in ANSI C63.10-2013, clause 8.3 for FM transmitters that inject a signal directly into a vehicle?s wiring system through the CLA socket. The use of the conducted test procedure is limited to this particular type of FM transmitter based on the research by the ANSI-ASC C63 standards committee that determined the correlation between the radiated and conducted measurement methods.

In-situ measurements are to be performed (see ANSI C63.10-2013, clause 8.4) for equipment designs not specifically addressed in ANSI C63.10-2013. Section 15.31(d) specifies that radiated emission measurements should be performed in at least three typical installations. The grantee is responsible for a design that is compliant in all types of vehicles in which the device is used. Therefore, measurements of the device must be made with the transmitter installed in at least three different vehicles. A large, midsize and compact vehicle must be chosen based on models in the targeted market. Test methods are provided using a vehicle turntable or without a vehicle turntable.

The measurement procedure for determining the occupied bandwidth of the FM transmitter is found in ANSI C63.10-2013, clause 8.7.

Note: ANSI C63.10-2013 also uses the term, FM modulator, interchangeably with the term FM transmitter. For example, many portable satellite radio receivers have built-in FM modulators or transmitters, which are designed to permit users to listen to satellite radio over a car radio on unused FM frequencies.


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