dm00061745

AN4147
Application note
Using the SPIRIT1 transceiver under FCC title 47 part 15 in the
315 MHz band
By Placido De Vita
Introduction
The SPIRIT1 is a very low power RF transceiver, intended for RF wireless applications in the
sub-1 GHz band. It is designed to operate in both the license-free ISM and SRD frequency
bands at 169, 315, 433, 868, 915 and 920 MHz.
This application note outlines the expected performance when using the SPIRIT1 under
FCC title 47 part 15 [2] in the 315 MHz band. There are no specific requirements in this
band, no specific use and no channel spacing are defined.
For details on the regulatory limits in the 315 MHz frequency band, please refer to the FCC
Title 47 Part 15 regulations [2].
These can be downloaded from:
http://wireless.fcc.gov/index.htm?job=rules_and_regulations.
August 2012
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Contents
AN4147
Contents
1
An overview of FCC regulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1
Part 15.231 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2
Parts 15.205 and 15.209 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2
Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3
Transmitter parameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1
Spurious RF conducted emission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4
Receiver parameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5
Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
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AN4147
An overview of FCC regulations
1
An overview of FCC regulations
1.1
Part 15.231
Devices operating in the 315 MHz band must comply with section 15.231 of the FCC Title 47
Part 15 [2] regulations. The provisions in section 15.231 are restricted to periodic operation
within the 40.66 - 40.70 MHz band and above 70 MHz. The intentional radiator is restricted
to the transmission of a control signal such as those used with alarm systems, door
openers, remote switches, etc. Continuous transmissions, voice, video and radio control of
toys are not permitted. Data is permitted to be sent with a control signal.
To comply with the provisions for periodic operation, the following conditions must be meet:
●
A manually operated transmitter shall employ a switch that will automatically deactivate
the transmitter within not more than 5 seconds of being released. A transmitter
activated automatically shall cease transmission within 5 seconds after activation.
●
Periodic transmissions at regular predetermined intervals are not permitted. However,
polling or supervision transmissions, including data, to determine system integrity of
transmitters used in security or safety applications are allowed if the total duration of
transmissions does not exceed 2 seconds per hour.
●
Intentional radiators which are employed for radio control purposes during
emergencies involving fire, security and safety of life, when activated to signal an
alarm, may operate during the pendency of the alarm condition.
●
In addition to the provisions of 15.205, the field strength of emissions from intentional
radiators operated under this section shall not exceed the values in Table 1. The field
strength limits are specified at a distance of 3 meters.
●
The limits on the field strength of the spurious emissions in the Table 1 are based on
the fundamental frequency of the intentional radiator. Spurious emissions shall be
attenuated to the average limits shown in this table or to the general limits shown in
section 15.209, whichever limit permits higher field strength.
●
The bandwidth of the emission shall be no wider than 0.25% of the center frequency.
Bandwidth is determined at the points 20 dB down from the modulated carrier.
●
Intentional radiators may operate at a periodic rate exceeding that specified in point 1
and may be employed for any type of operation, including operation prohibited in point
1. In this case, the max field strength is different and is shown in the Table 2. The
device operating in the condition described in this point shall be provided with a means
for automatically limiting operation so that the duration of each transmission shall not
be greater than 1 second and the silent period between transmissions shall be at least
30 times the duration of the transmission, but in no case less than 10 seconds.
Table 1.
Field strength of emissions for normal working conditions
Fundamental frequency Field strength of fundamental
[MHz]
[µV/m]
Field strength of spurious emission
[µV/m]
40.66 – 40.70
2250
225
70 – 130
1250
125
130 – 174
1250 to 3750
125 to 375
174 – 260
3750
375
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An overview of FCC regulations
Table 1.
AN4147
Field strength of emissions for normal working conditions (continued)
Fundamental frequency Field strength of fundamental
[MHz]
[µV/m]
260 – 470
3750 to 12500
375 to 1250
Above 470
12500
1250
Table 2.
Field strength of emissions for particular working conditions
Fundamental frequency Field strength of fundamental
[MHz]
[µV/m]
1.2
Field strength of spurious emission
[µV/m]
Field strength of spurious emission
[µV/m]
40.66 – 40.70
1000
100
70 – 130
500
50
130 – 174
500 to 1500
50 to 150
174 – 260
1500
150
260 – 470
1500 to 5000
150 to 500
Above 470
5000
500
Parts 15.205 and 15.209
As described in the previous paragraphs, radiated harmonics and spurious emissions of
devices that comply with section 15.231 and which fall within the restricted bands, as
defined in FCC section 15.205, must comply with the radiated emission limits specified in
FCC section 15.209. In addition to the provisions of 15.205, the field strength of emissions
from intentional radiators operated under this section shall not exceed the values in Table 1.
The field strength limits are specified at a distance of 3 meters.
Section 15.205 shows the bands where only spurious emissions are permitted. The field
strength of emissions appearing within these frequency bands shall not exceed the limits
shown in section 15.209. The following tables show the restricted bands as defined in
section 15.205 and the radiated and conducted emission limits are defined in section
15.209.
Table 3.
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Restricted bands defined in section 15.205
MHz
MHz
MHz
GHz
0.090 – 0.110
16.42 – 16.423
399.9 – 410
4.5 – 5.15
0.495 – 0.505
16.69475 – 16.69525
608 – 614
5.35 – 5.46
2.1735 – 2.1905
16.80425 – 16.80475
960 – 1240
7.25 – 7.75
4.125 – 4.128
25.5 – 25.67
1300 – 1427
8.025 – 8.5
4.17725 – 4.17775
37.5 – 38.25
1435 – 1626.5
9.0 – 9.2
4.20725 – 4.20775
73 – 74.6
1645.5 – 1646.5
9.3 – 9.5
6.215 – 6.218
74.8 – 75.2
1660 – 1710
10.6 – 12.7
6.26775 – 6.26825
108 – 121.94
1718.8 – 1722.2
13.25 – 13.4
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AN4147
An overview of FCC regulations
Table 3.
Restricted bands defined in section 15.205 (continued)
MHz
MHz
MHz
GHz
6.31175 – 6.31225
123 - 138
2200 – 2300
14.47 – 14.5
8.291 – 8.294
149.9 – 150.05
2310 – 2390
15.35 – 16.2
8.362 – 8.366
156.52475 – 156.52525
2483.5 – 2500
17.7 – 21.4
8.37625 – 8.38675
156.7 – 156.9
2690 – 2900
22.01 – 23.12
8.41425 – 8.41475
162.0125 – 167.17
3260 – 3267
23.6 – 24.0
12.29 – 12.293
167.72 – 173.2
3332 – 3339
31.2 – 31.8
12.51975 – 12.52025
240 – 285
3345.8 – 3358
36.43 – 36.5
12.57675 – 12.57725
322 – 335.4
3600 – 4400
Above 38.6
13.36 – 13.41
Table 4.
Radiated and conducted emission limits defined in section 15.209
Frequency [MHz]
Field strength [µV/m]
Measurement distance [m]
Conducted [dBm]
0.009 – 0.490
2400/f [kHz]
300
12.4 – 20*log(f)kHz
0.490 – 1.705
24000/f [kHz]
30
12.4 – 20*log(f)kHz
1.705 – 30.0
30
30
– 46
30– 88
100
3
– 56
88 – 216
150
3
– 52
16 – 960
200
3
– 49
960
500
3
– 41
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Application circuit
2
AN4147
Application circuit
Figure 1 shows an image of the SPIRIT1 application board. The application is made up of 2
boards: a daughterboard and a motherboard. The daughterboard contains the SPIRIT1 with
the circuits necessary for it to work. For correct functionality, the daughterboard must be
plugged into the motherboard (see Figure 2) by two header 5x2 connectors (J6 and J7).
The motherboard is provided with an STM32L152VBT6 microcontroller to correctly program
the transceiver. The microcontroller is programmed with firmware developed for the SPIRIT1
application. A graphical user interface (GUI) is developed to correctly program the SPIRIT1.
The daughterboard is provided with a 52 MHz XTAL to provide the correct oscillator to the
SPIRIT1.
The SPIRIT1 has an internal SMPS that drastically reduces power consumption, making it
the best-in-class for applications on this bandwidth. The SMPS is fed from the battery (1.8 V
to 3.6 V) and provides the device with a programmable voltage (1.4 V typical). An SMA
connector is present to connect the board to an antenna or to instrumentation to verify the
correct functionality and verify the ETSI standard request.
A few of passive devices (inductors and capacitors) are used for matching/filtering in the
power amplifier (PA) and balun network for the receiver.
To reduce application costs, the SPIRIT1 is designed to work without an external antenna
switch. The daughterboard is designed to show the SPIRIT1 functionality in this condition.
Clearly, an application with antenna switch can be realized, but this is not described in this
document.
Figure 1.
SPIRIT1 application daughterboard
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Application circuit
Figure 2.
SPIRIT1 application daughterboard plugged into the motherboard
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4
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R_0R0_0402
B2=433MHz
6
R8
XOUT
B3=868MHz
B3=915MHz
B3=920MHz
R_0R0_0402
R11
R_0R0_0402
R10
R_0R0_0402
R9
8
R_0R0_0402
GPIO_1
7
B1=315MHz
XIN
R7
GPIO_2
9
Mount
resistor
relative to
used band
C_12P_0402_C0G_J_50
RXP
B0=169MHz
VBAT2
11
12
13
14
15
C_TBD_0402_C0G
C19
L7
L_10U_0805
C_10P_0402_C0G_J_50
C10
REXT
TX
SMPS2
21
R_0R0_0402
GPIO_3
10
C9
RXN
XTAL
SDn
SMPS1
GND
NX3225GA-xxMHz (XTAL) Y1
VREG
SPIRIT1_2
4 SCLK
5
CSn
VBAT1
R6
SDO
SDI
SCLK
CSn
20
3 SDI
19
J7
HEADER 5X2
C21
C_100p_0402_C0G
C_100n_0402_X7R
C0
17
2 SDO
18
1 GPIO_0
U1
C_330p_0402_C0G
C22
SDn
C20
C_1U_0603_X7R_K_6V3
16
GPIO0
GPIO3
GPIO2
GPIO1
SPIRIT_DUMMY1
VCC_RF
L8
C4
C1
L_TBD_0402
L2
C_TBD_0402_C0G
L_TBD_0402
L4
C_TBD_0402_C0G
C5
C_TBD_0402_C0G
C_TBD_0402_C0G
C8
C13
C_TBD_0402_X7R
C_TBD_0402_C0G C_TBD_0402_C0G
C2
C3
C_TBD_0402_C0G
L3 L_TBD_0402
C_TBD_0402_C0G
C7
C_TBD_0402_C0G
L_TBD_0402
L_TBD_0402
L6
C6
L5
C_TBD_0402_C0G
C15
L1
C14
C12
C_100n_0402_X7R
L_TBD_0402
L9
C11
C_1U_0603_X7R_K_6V3
R13
R_TBD_0402
R12
R_TBD_0402
L0
L_TBD_0402_50M
L_TBD_0402
L_TBD_0402
DUMMY3
3V3
J1
RF_IN/OUT
Figure 3.
DUMMY3
J6
HEADER 5X2
SPIRIT_DUMMY2
Application circuit
AN4147
Daughterboard schematic
AM13166v1
AN4147
3
Transmitter parameter
Transmitter parameter
All of the measurements reported here are measured using the following parameters:
Tc = 25 ° C, Vdd = 3.0 V, f = 315 MHz, unless otherwise specified.
Regarding the output power and emission, the standard specifies the maximum field
strength (µV/m). Microvolts per meter (µV/m) are the units used to describe the strength of
an electric field created by the operation of a transmitter. A particular transmitter that
generates a constant level of power (watts) can produce electric fields of different strengths
depending on the type of antenna connected to it. Because it is the electric field that causes
interference to authorized radio communications, and since particular electric field strength
does not directly correspond to a particular level of transmitter power, the emission limit of
short range devices are specified in field strength.
In order to simplify the testing environment, a conversion from the field strength to output
power is done, since the latter is easier to measure. Although the precise relation between
power and field strength can depend on a number of additional factors, a commonly-used
equation to approximate the field strength (V/m) and the power (W) is:
Equation 1
(P * G)/(4 * d2) = (E2)/(120 * Π)
where:
–
P = transmitter power (EIRP) in watts
–
G = gain of the transmitter antenna relative to an isotropic source
–
d = distance of the measuring point from the electrical center of the antenna in
meters
–
E = field strength in volts/meter
–
4 * d2 = surface area of the sphere centered at the radiating source whose surface
is d meters from the radiating source
–
120 * Π = characteristic impedance of free space in ohms
Assuming a unity gain antenna (G = 1) and considering the measurement distance of 3
meters (d = 3), a formula can be summarized with:
Equation 2
P = 0.3 * E2
The field strength of the fundamental at 315 MHz is not given directly but has to be
calculated from the two values (260 to 470 MHz) defined in Table 1. The calculated value of
the field strength of the fundamental at 315 MHz is 6043.5 µV/m which corresponds,
applying the formula above, to a value of - 19.6 dBm at 3 m distance. In a similar manner,
the field strength of the spurious emissions must be lower than 604.35 µV/m which
corresponds, applying the formula above, to a value of - 35 dBm at 3 m distance.
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Transmitter parameter
3.1
AN4147
Spurious RF conducted emission
According to FCC section 15.231, the field strength of all emissions from intentional
radiators outside the fundamental and the band defined in section 15.205 must be lower
than the values defined in Table 1. The field strength limits are specified at a distance of 3
meters. The limits on the field strength of the spurious emissions in the Table 1 are based on
the fundamental frequency of the intentional radiator. Spurious emissions shall be
attenuated to the average limits shown in this table or to the general limits shown in section
15.209, whichever limit permits higher field strength.
According to section 15.33, for an intentional radiator operating below 10 GHz, the
frequency range of measurements must be up to the tenth harmonic of the highest
fundamental or to 40 GHz, whichever is lower. The SPIRIT1 highest fundamental frequency
is 315 MHz, so the tenth harmonic is 3.15 GHz. The measurements are performed up to 5
GHz.
In Figure 4 and 5 the spurious conducted emissions and the FCC emission mask are
shown. The carrier is unmodulated. The SPIRIT1 is fully compliant with the conducted
spurious emission requirements.
Figure 4.
TX spurious emission below 1 GHz
-10
Output power
FCC mask
-20
Output power [dBm]
-30
-40
-50
-60
-70
-80
-90
0.0E+00
1.0E+08
2.0E+08
3.0E+08
4.0E+08
5.0E+08 6.0E+08
Frequency [Hz]
7.0E+08
8.0E+08
9.0E+08
1.0E+09
AM13274v1
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AN4147
Transmitter parameter
TX spurious emission above 1 GHz
-20
Output power
FCC mask
-30
-40
Output power [dBm]
Figure 5.
-50
-60
-70
-80
1.0E+09
1.5E+09
2.0E+09
2.5E+09
3.0E+09
3.5E+09
Frequency [Hz]
4.0E+09
4.5E+09
5.0E+09
AM13275v1
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Receiver parameter
4
AN4147
Receiver parameter
No specific requirements are defined for FCC compliance of the receiver in US FCC Title 47
Part 15 [2] in the 315 MHz band. No measurements were done for the receiver.
5
12/14
Reference
1.
SPIRIT1 datasheet
2.
FCC title 47 Part 15: “Radio frequency devices”
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6
Revision history
Revision history
Table 5.
Document revision history
Date
Revision
06-Aug-2012
1
Changes
Initial release.
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AN4147
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