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Chapter 2

Chapter 2. Radio Frequency Spectrum. Overview. Radio Frequencies RF Bands and Management RF Propagation Mixing of Frequencies Modulation. >>. Electromagnetic Frequencies. Electromagnetic spectrum Radio frequencies Visible light and Infrared Ultraviolet X-rays Gamma rays

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Chapter 2

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  1. Chapter 2 Radio Frequency Spectrum

  2. Overview Radio Frequencies RF Bands and Management RF Propagation Mixing of Frequencies Modulation >>

  3. Electromagnetic Frequencies • Electromagnetic spectrum • Radio frequencies • Visible light • and • Infrared • Ultraviolet • X-rays • Gamma rays • RF has the longest wavelength • Gamma rays have the shortest >>

  4. RF and Visible Light Radio Frequencies >>

  5. Frequency and Wavelength • RF travels at 300,000,000 meters/second • In free space • 186,000 statute miles/second • Wavelength = speed of propagation / frequency • λ (in meters) = 300 / f (in MHz) >>

  6. Frequency Terms 1 cycle per second = 1 Hertz (Hz) 1,000 Hz = 1 kiloHertz (kHz) 1,000 KHz = 1 MegaHertz (MHz) 1,000 MHz = 1 GigaHertz (GHz) 2 MHz is 150 meter wavelength 4 MHz is 75 meters 15 MHz is 20 meters 150 MHz is 2 meters >>

  7. Electromagnetic Waves - 1 • AC Current in a wire creates a magnetic field • Example: the hum in AM radio under a power line • RF in a wire radiates an electromagnetic field >>

  8. Electromagnetic Waves - 2 • RF in a wire radiates an electromagnetic field • If wire is significant fraction of a wavelength • Strength varies with square of distance • called “space attenuation” • Can detect this weak electromagnetic field • In an antenna • better if significant fraction of a wavelength • Even at considerable distance • direct TV broadcast from a satellite • GPS signal from a satellite >>

  9. RF Bands and Management Radio frequency bands Radio frequency management >>

  10. Radio Frequency Bands DesignationAbbreviationFrequencyWavelength Very Low Frequency VLF9 kHz - 30 kHz 33 km – 10 km Low Frequency LF30 kHz - 300 kHz 10 km – 1 km Medium FrequencyMF 300 kHz - 3 MHz 1 km – 100 m High FrequencyHF 3 MHz - 30 MHz 100 m – 10 m Very High Frequency VHF30 MHz - 300 MHz 10 m – 1 m Ultra High Frequency UHF 300 MHz - 3 GHz 1 m - 100 mm Super High Freq SHF3 GHz - 30 GHz 100 mm – 10 mm Extremely High Freq EHF 30 GHz - 300 GHz 10 mm – 1 mm >>

  11. Marine Radio Frequencies • MF 2.0 to 3.0 MHz USB • 2182.0 kHz emergency voice and hailing • 2187.5 kHz DSC emergency and hailing • HF 4.0 to 27.5 MHz USB • 6215.0 kHz emergency voice • 8291.0 kHz emergency voice • No DSC emergency frequency • VHF 156 to 162 MHz FM • Channel 16 (156.800 MHz) emergency voice • Channel 70 (156.525 MHz) DSC emergency • Weather 162.400 to 162.550 MHz >>

  12. Electronics by Frequency >>

  13. RF Management • Internationally • International Telecommunications Union (ITU) • U.S. is a signatory • In United States • National Telecommunication and Information Administration (NTIA) • Federal Communications Commission (FCC) • U.S. Communications Act of 1934 • CFR Title 47 Part 80 on maritime radio >>

  14. Spectrum Allocation >>

  15. RF Propagation Radio Line-of-Sight Ground Wave Sky Wave Skip Zone Ionosphere Layers Propagation Software Signal Reliability Rules of Thumb >>

  16. Radio Line-of-Sight • Range is a function of antenna height • D (in nm) = 1.32 * √ h (antenna height in feet) • VHF (150 MHz) uses this mode >>

  17. Ground Waves • Ground Wave follows Earth's surface • MF (2 to 3 MHz) uses this mode • Longer range at night >>

  18. Ionosphere Layers • At night there is only a consolidated “F” layer • With good HF sky wave refraction • During daylight there is more attenuation, less refraction • MF limited to ground wave propagation >>

  19. Escaping Sky Waves • RF over 50 MHz “escapes” • Ideal between Earth and satellites >>

  20. Sky Waves • Refracted by Ionosphere • HF and VHF up to 50 MHz uses this mode • Amount of refraction is a function of frequency >>

  21. Refraction vs Frequency • Refraction decreases as frequency increases • At “Critical Frequency” radio wave “escapes” >>

  22. Skip Zone • Note Ground Wave coverage • Note Sky Wave coverage • No coverage gap is “Skip Zone” >>

  23. Sky Waves - 2 • Refraction from “E” or “F” Layer • Only one combined “F” layer at night • One Hop and Two Hop propagation >>

  24. Space Attenuation • Strength of signal is inversely proportional to square of the distance from transmitter >>

  25. Propagation Software • Suggests HF frequency based on: • Date and time of day • Distance and direction to be covered • PACTOR HF modem includes proprietary SW • Pactor HF data modem covered in Chapter 7 • VOACAP ver 8.0410 (10 Apr 08) • Communications analysis and prediction • Free from Greg Hand (retired from NTIA/ITS) • ASAPS ver 5.2 (Mar 06) • Advanced Stand-Alone Prediction System • Approx $275 (US) from Australian government >>

  26. Propagation Models • Inputs • Date and time • Locations (yours and distant end) • Other parameters • Output • F-layer MUF (Maximum Usable Frequency) • F-layer FOT (Frequency of Optimum Transmission) • F-layer LUF (Lowest Usable Frequency) • Path probability • Other parameters >>

  27. VOACAP input – ASAPS output >>

  28. Signal Reliability • Ionosphere Changes • Day vs night • Spring/summer vs fall/winter • 28-day sun cycle and 11-year sunspot cycle • Averages used in these charts >>

  29. Rules of Thumb 1. If you can hear them, they can hear you 2. MF (2 to 3 MHz) – Ground wave propagation Day: at least 50 miles and most probably 100 nm Night: out to 200 miles or more 3. 4 to 8 MHz Day: probably 50 miles via ground wave and 50 to 250 miles via sky wave Night: between 150 to 1,500 nm via sky wave 4. 10 to 20 MHz Day: possibly 50 miles via ground wave and 250 to 1,500 nm via sky wave Night: 400 to over 2,500 miles via sky wave >>

  30. Mixing of Frequencies 10 kHz 1 kHz (Audio) 1 kHz (Audio) 10 kHz 90 kHz 10 MHz (RF) 100 kHz 10.000 MHz (RF) 100 kHz 110 kHz 9.999 MHz (RF) Mixer 10.001 MHz (RF) • Inputs: two frequencies • Outputs • Two original frequencies • Difference • Sum >>

  31. Modulation • Continuous Wave (CW) • Amplitude Modulation • Full Carrier Double Sideband (AM) • Suppressed Carrier Single Sideband (SSB) • Other variations • Frequency Modulation (FM) >>

  32. Continuous Wave (CW) • First way of encoding the RF carrier • Turn the carrier “ON” and “OFF” • Short “dots” and long “dashes” • Morse Code “K” Code was: “USPS Marine Electronics” >>

  33. Amplitude Modulation (AM) Amplitude vs Frequency Amplitude vs Time • Full Carrier Double Sideband • Details in Chapter 7 • Mixer with Audio and RF in and only RF out • In: 1 kHZ and 10 MHz • Out: 9.999 MHz, 10.000 MHz and 10.001 MHz >>

  34. Single Sideband (SSB) Amplitude vs Frequency USB only • Suppressed Carrier Single Sideband • Details in Chapter 7 • Mixer with Audio and RF in and only USB out • In: 1 kHZ and 10 MHz • Out: 10.001 MHz (Carrier & Lower Sideband suppressed) >>

  35. Other AM Variants • Other variants • Suppressed carrier, double sideband • Suppressed carrier, lower sideband >>

  36. Frequency Modulation • Details in Chapter 3 • Audio Amplitude changes frequency • Audio Frequency changes rate of frequency swing >>

  37. Summary • Frequency terms: Hz, kHZ, MHz, GHz • Marine Frequency Bands: MF, HF, VHF • RF Propagation • Radio line-of-sight: D (in nm) = 1.32 √ h (in feet) • Ground wave: 50 to 100 nm; MF primary mode • Sky wave: HF primary mode; farther at night • the higher the frequency, the greater the distance • Skip zone: between ground wave and sky wave • Mixing of frequencies • Two original, plus sum and difference • Modulation: CW, AM, SSB and FM >>

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