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 reg-
ulation 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 con-
tent, 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 sig-
nals such as alarm systems, door openers, remote switches, etc. Radio control of toys is not permitted, nor is continuous trans-
mission such as voice or video. Data transmission other than a recognition code is not permitted. Transmission 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 fre-
quency 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 fun-
damental 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 calcu-
lated 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 funda-
mental, the reference spurs, and the harmonics of the fundamental up through the tenth harmonic are calculated in the follow-
ing table The occupied bandwidth limit is 787.5kHz. As shown in Table A, the fifth, seventh, and ninth harmonics 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).
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
12 of 22
Rev A17 DS060712
RFMD [ RF MICRO DEVICES ]
