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Download Embedded Meets RF Evan Lojewski RF Primer Terminology / Intro
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Embedded Meets RF Evan Lojewski RF Primer • Terminology / Intro • RF Options • Certification Terminology • Decibel - logarithmic scale • Channel - subdivided portion of spectrum • Carrier - center frequency of channel / transmission • DNR - dynamic range Decibel • dB is unit-less, denotes logarithmic • value dB = 10log10(value) • value = 10^(value dB / 10) • Standard exponential rules apply • Cannot multiply value together db Suffixes • dBW: Watts • dBm: miliWatts • dBi: forward gain of antenna • dBc: relative to carrier Gain / Loss • Gain is the Amplification of signal (unitless). 3db gain is an amplification of 2x. • Linear: Power * gain(amp) = final power • dB: Power + gain(amp) = final power • Linear: Gain = 1/Loss • dB: Gain = - Loss Sample Calculations • 5dB + 10dBw = 15dBw • -3dBw = 27dBm • -3dBm + 3dBm = ???? • 10dBm = 10 mW = 0.01 W More Examples • 3dB ~= 2 • 6dBm ~= 4 mW • 13dB ~= 20 • 20dB = 100 Test Equipment • Spectrum Analyzer • Verify emissions • demodulate packet • Network Analyzer • Impedance Matching • Power Meter • Anechoic Chamber RF Options • Don’t do it -> go wired (really) • Modules • PDB Design Wires: The easy option • Batteries are annoying • Reliability • Throughput • Don’t have to mess with the FCC... much RF Frequencies: ISM • 2.45GHz: Wifi, Bluetooth, 802.15.4, Cordless Phones • 1W peak power • 915 MHz: UHF RFID, Cell Phones • 1W peak power Classic Bluetooth • Interoperability • Android • Power hungry • 3mA connected • 30mA connecting Classic Bluetooth • AT Command Set • Control • UART passthrough (SPP) • Transparent to software Bluetooth Smart • Interoperability • iOS • Window 8 • Low Power • ~40uA - 150uA connected • 18mA transmitting (max ~300us burst) XBee • Serial passthrough • Pair two devices Wifi • Interoperability • Anything with network access • web pages • telnet • Complex - TCP/IP • High Power Proprietary • Non-Interoperability • Vendor lock in • Minimal overhead • Depending on implementation, can be very low power. RF Modules: 2.4Ghz Module Standards Power RX (idle) Throughput XBee 802.15.4 40 mA 250Kbps GS1011MI P 802.11b 150mA (150uA) 11Mbps RN-171 802.11b/g 120mA (15mA) 54Mbps nRF24L01 Proprietary 11.3mA (22uA) + 2Mbps RN-42 Bluetooth 30mA (26uA) 240Kbps BluetoothL BR-LE4.0 E 27mA (0.9uA) 1Mbps RF Modules: 2.4Ghz Module Interface XBee UART GS1011MI P UART / SPI Custom 90dB 28 RN-171 UART / SPI Custom 93dB 30 nRF24L01 + SPI Packet 82dB 20 RN-42 UART / SPI Passthrough 84dB 16 UART / SPI AT Commands BR-LE4.0 API DNR $ Passthrough 99dB 23 96dB 119 Custom PCB vs Module • Lower Cost than modules in volume • Full control over design • Smaller size • Must go through complete certification process PCB Considerations • ε : Affects thickness of PCB • Ground Plane • Controlled Impedance • Manufacturer Recommendations r FCC Regulations • Covers Unintentional Radiator • And Intentional radiators Unintentional Radiators • Digital Device operating at 9kHz+ • Must be Verified. • Manufacture makes measurements. • Submittal of measurements / sample unit only required if FCC asks. Intentional Radiators • Digital Device operating at 9kHz+ • Must have a Declaration of Conformity • You declare part complies with FCC regulations. FCC Certification • Form 731 • $1265.00 Fee • Measurement Results / Report • System Block Diagram FCC Exceptions: Subassemblies • Subassemblies • Do not need to be certified / verified • End user will need to FCC certify • Home-built devices • Up to 5 of any non-marketed, non-kit • Personal use only. FCC Requirements: 15.247 (2.4GHz) • 1W peak Power • spurious emissions: 20dB below carrier • And many more... FCC Requirements: 47 CFR 2 • Must retain description of faciility • List of equipment used • Must retain original drawings, records of procedures and measurements made. • Retain all data required to show conformity. PCB Considerations • Software? • Module vendors usually give you their stack and examples • Chip vendors don’t support small companies often. PCB Considerations • Antenna • Chip Antenna? (expensive) • Trace Antenna? (cheap) • RF Connector? (expensive) • Impedance Matching • balun? • Tuning components References • FCC 47 CFR 15: Radio Devices • FCC 47 CFR 2 Subpart J: Equipment Auth • http://www.sparkfun.com/tutorials/398 • Example FCC report: http://faenl.msi.com/ftp/CE%20Docume nts/68xx/BTHub/41104402RP1%20Part%2015.247.pdf
