RF2516
RF2516 Typical Applications
FCC Part 15.231 Periodic Transmitter - 315MHz Automotive Keyless Entry Transmitter
The following information is taken or paraphrased from the Code of Federal Regulations Title 47, Part 15, Section 231
(47 CFR 15.231). Part 15 discusses radio frequency devices and section 231 discusses periodic transmissions. Please
refer to the regulation itself as the final authority. Additional information may be found on the Internet at www.fcc.gov.
To highlight the main guidelines outlined by this section, there are five main limitations: operating frequency, transmission
content, transmission duration, emission bandwidth, and spurious emissions.
Part 15.231 allows operation in two bands: 40.66MHz to 40.70MHz and above 70MHz. Transmission is limited to control
signals such as alarm systems, door openers, remote switches, etc. Radio control of toys is not permitted, nor is contin-
uous transmission such as voice or video. Data transmission other than a recognition code is not permitted. Transmis-
sion time is limited to 5 seconds (paragraph a) or for 1 second with greater than ten seconds off (paragraph e).
Emission bandwidth between 70MHz and 900MHz can not be more than 0.25% of the center frequency. Above
900MHz, the emission bandwidth cannot be greater than 0.50% of the center frequency. The emission bandwidth is
determined from the points that are 20dB down from the modulated carrier. This corresponds to an occupied bandwidth
of 4.5MHz at a center frequency of 902MHz, 1.1MHz at 433MHz, and 788kHz at 315MHz.
Spurious emissions limits are listed in tabular form for various frequency ranges in the Section 231. Above 470MHz with
a manually activated transmitter, the fundamental field strength at a distance of 3 meters shall not exceed
12,500microvolts/meter. The spurious emissions shall not exceed 1,250microvolt/meter at a distance of 3meters above
470MHz. Refer to Appendix A for a method of converting field strength to power.
In the frequency range of 260MHz to 470MHz, one needs to linearly interpolate the maximum emissions level for both
the fundamental and spurious emissions. The equation for this line is given by:
2
3
1
--
--
EμV = 41 ⋅ FreqMHz – 7083
m
3
-------
This equation is derived from the endpoints of the frequency range and their respective field strengths. Note that the field
strength is in microvolts per meter and the frequency is in megahertz. To determine the spurious level, divide the level
calculated above for the spurious frequency by ten.
As an example, assume the fundamental is 315MHz and the reference frequency is 9.8MHz. The field strengths of the
fundamental, the reference spurs, and the harmonics of the fundamental up through the tenth harmonic are calculated in
the following table The occupied bandwidth limit is 787.5kHz. As shown in Table A, the fifth, seventh, and ninth harmon-
ics fall into restricted bands as called out in section 15.205. The limits for these restricted bands are called out in section
15.209. The power level in the last column is the level if the output is connected directly to a spectrum analyzer. Refer to
Appendix A as to how this column was calculated.
Local Oscillator Source
Since the RF2516 has a phase-locked VCO, it can be used as a signal source. The device is an ASK/OOK transmitter,
with the data provided at the MOD IN pin. When the MOD IN is a high logic level, the carrier is transmitted. When MOD
IN is a low logic level, then the carrier is not transmitted. Therefore, to use the RF2516 as signal source, simply tie the
MOD IN pin to the supply voltage, through a suitable series resistor (minimum 3kΩ).
Rev A17 060712
11-11
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