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Embedded Meets RF

This guide provides an in-depth overview of essential RF terminology, including decibels, channel definitions, and dynamic range. It explains key concepts such as gain and loss in signal transmission, how to calculate dB values, and the significance of RF frequencies like 2.45GHz for common technologies. Additionally, it covers certification requirements for intentional and unintentional radiators under FCC regulations, offering insights into PCB design considerations and compliance procedures. Ideal for engineers and DIY enthusiasts looking to navigate RF design and certification processes.

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Embedded Meets RF

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  1. Embedded Meets RF • Evan Lojewski

  2. RF Primer • Terminology / Intro • RF Options • Certification

  3. Terminology • Decibel - logarithmic scale • Channel - subdivided portion of spectrum • Carrier - center frequency of channel / transmission • DNR - dynamic range

  4. Decibel • dB is unit-less, denotes logarithmic • value dB = 10log10(value) • value = 10^(value dB / 10) • Standard exponential rules apply • Cannot multiply value together

  5. db Suffixes • dBW: Watts • dBm: miliWatts • dBi: forward gain of antenna • dBc: relative to carrier

  6. 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

  7. Sample Calculations • 5dB + 10dBw = 15dBw • -3dBw = 27dBm • -3dBm + 3dBm = ???? • 10dBm = 10 mW = 0.01 W

  8. More Examples • 3dB ~= 2 • 6dBm ~= 4 mW • 13dB ~= 20 • 20dB = 100

  9. Test Equipment • Spectrum Analyzer • Verify emissions • demodulate packet • Network Analyzer • Impedance Matching • Power Meter • Anechoic Chamber

  10. RF Options • Don’t do it -> go wired (really) • Modules • PDB Design

  11. Wires: The easy option • Batteries are annoying • Reliability • Throughput • Don’t have to mess with the FCC... much

  12. RF Frequencies: ISM • 2.45GHz: Wifi, Bluetooth, 802.15.4, Cordless Phones • 1W peak power • 915 MHz: UHF RFID, Cell Phones • 1W peak power

  13. Classic Bluetooth • Interoperability • Android • Power hungry • 3mA connected • 30mA connecting

  14. Classic Bluetooth • AT Command Set • Control • UART passthrough (SPP) • Transparent to software

  15. Bluetooth Smart • Interoperability • iOS • Window 8 • Low Power • ~40uA - 150uA connected • 18mA transmitting (max ~300us burst)

  16. XBee • Serial passthrough • Pair two devices

  17. Wifi • Interoperability • Anything with network access • web pages • telnet • Complex - TCP/IP • High Power

  18. Proprietary • Non-Interoperability • Vendor lock in • Minimal overhead • Depending on implementation, can be very low power.

  19. RF Modules: 2.4Ghz

  20. RF Modules: 2.4Ghz

  21. Custom PCB vs Module • Lower Cost than modules in volume • Full control over design • Smaller size • Must go through complete certification process

  22. PCB Considerations • εr: Affects thickness of PCB • Ground Plane • Controlled Impedance • Manufacturer Recommendations

  23. FCC Regulations • Covers Unintentional Radiator • And Intentional radiators

  24. Unintentional Radiators • Digital Device operating at 9kHz+ • Must be Verified. • Manufacture makes measurements. • Submittal of measurements / sample unit only required if FCC asks.

  25. Intentional Radiators • Digital Device operating at 9kHz+ • Must have a Declaration of Conformity • You declare part complies with FCC regulations.

  26. FCC Certification • Form 731 • $1265.00 Fee • Measurement Results / Report • System Block Diagram

  27. 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.

  28. FCC Requirements: 15.247 (2.4GHz) • 1W peak Power • spurious emissions: 20dB below carrier • And many more...

  29. 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.

  30. PCB Considerations • Software? • Module vendors usually give you their stack and examples • Chip vendors don’t support small companies often.

  31. PCB Considerations • Antenna • Chip Antenna? (expensive) • Trace Antenna? (cheap) • RF Connector? (expensive) • Impedance Matching • balun? • Tuning components

  32. 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%20Documents/68xx/BTHub/41104402-RP1%20Part%2015.247.pdf

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