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Chapter 2 Radio Frequency Spectrum MComm-Ch2 - 1.

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Presentation on theme: "Chapter 2 Radio Frequency Spectrum MComm-Ch2 - 1."— Presentation transcript:

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2 Chapter 2 Radio Frequency Spectrum MComm-Ch2 - 1

3 Overview Radio Frequencies RF Bands and Management RF Propagation Mixing of Frequencies Modulation MComm-Ch2 - 2 >>

4 Electromagnetic Frequencies MComm-Ch2 - 3 Electromagnetic spectrum  Radio frequencies  Visible light  and  Infrared  Ultraviolet  X-rays  Gamma rays RF has the longest wavelength Gamma rays have the shortest >>

5 RF and Visible Light MComm-Ch2 - 4 Radio Frequencies >>

6 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) MComm-Ch2 - 5 >>

7 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 MComm-Ch2 - 6 >>

8 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 MComm-Ch2 - 7 >>

9 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 MComm-Ch2 - 8 >>

10 RF Bands and Management Radio frequency bands Radio frequency management MComm-Ch2 - 9 >>

11 Radio Frequency Bands Designation Abbreviation FrequencyWavelength Very Low Frequency VLF9 kHz - 30 kHz 33 km – 10 km Low Frequency LF30 kHz kHz 10 km – 1 km Medium Frequency MF 300 kHz - 3 MHz 1 km – 100 m High Frequency HF 3 MHz - 30 MHz 100 m – 10 m Very High Frequency VHF 30 MHz MHz 10 m – 1 m Ultra High Frequency UHF300 MHz - 3 GHz 1 m mm Super High Freq SHF3 GHz - 30 GHz 100 mm – 10 mm Extremely High Freq EHF30 GHz GHz 10 mm – 1 mm MComm-Ch >>

12 Marine Radio Frequencies MF 2.0 to 3.0 MHz USB  kHz emergency voice and hailing  kHz DSC emergency and hailing HF 4.0 to 27.5 MHz USB  kHz emergency voice  kHz emergency voice  No DSC emergency frequency VHF 156 to 162 MHz FM  Channel 16 ( MHz) emergency voice  Channel 70 ( MHz) DSC emergency  Weather to MHz MComm-Ch >>

13 Electronics by Frequency MComm-Ch >>

14 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 MComm-Ch >>

15 Spectrum Allocation MComm-Ch >>

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

17 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 MComm-Ch >>

18 Ground Waves Ground Wave follows Earth's surface MF (2 to 3 MHz) uses this mode Longer range at night MComm-Ch >>

19 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 MComm-Ch >>

20 Escaping Sky Waves RF over 50 MHz “escapes” Ideal between Earth and satellites MComm-Ch >>

21 Sky Waves Refracted by Ionosphere HF and VHF up to 50 MHz uses this mode Amount of refraction is a function of frequency MComm-Ch >>

22 Refraction vs Frequency Refraction decreases as frequency increases At “Critical Frequency” radio wave “escapes” MComm-Ch >>

23 Skip Zone Note Ground Wave coverage Note Sky Wave coverage No coverage gap is “Skip Zone” MComm-Ch >>

24 Sky Waves - 2 Refraction from “E” or “F” Layer  Only one combined “F” layer at night One Hop and Two Hop propagation MComm-Ch >>

25 Space Attenuation Strength of signal is inversely proportional to square of the distance from transmitter MComm-Ch >>

26 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 (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 MComm-Ch >>

27 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 MComm-Ch >>

28 VOACAP input – ASAPS output MComm-Ch >>

29 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 MComm-Ch >>

30 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 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 MComm-Ch >>

31 Mixing of Frequencies Inputs: two frequencies Outputs  Two original frequencies  Difference  Sum MComm-Ch kHz 100 kHz 10 kHz 100 kHz 90 kHz 110 kHz Mixer 1 kHz (Audio) 10 MHz (RF) MHz (RF) 1 kHz (Audio) MHz (RF) MHz (RF) >>

32 Modulation Continuous Wave (CW) Amplitude Modulation  Full Carrier Double Sideband (AM)  Suppressed Carrier Single Sideband (SSB)  Other variations Frequency Modulation (FM) MComm-Ch >>

33 Continuous Wave (CW) First way of encoding the RF carrier  Turn the carrier “ON” and “OFF”  Short “dots” and long “dashes”  Morse Code MComm-Ch “K” Code was: “USPS Marine Electronics” >>

34 Amplitude Modulation (AM) 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: MHz, MHz and MHz MComm-Ch Amplitude vs Frequency Amplitude vs Time >>

35 Single Sideband (SSB) 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: MHz (Carrier & Lower Sideband suppressed) MComm-Ch Amplitude vs Frequency USB only >>

36 Other AM Variants Other variants  Suppressed carrier, double sideband  Suppressed carrier, lower sideband MComm-Ch >>

37 Frequency Modulation Details in Chapter 3 Audio Amplitude changes frequency Audio Frequency changes rate of frequency swing MComm-Ch >>

38 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 MComm-Ch >>


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