Chapter 2Chapter 2

Radio FrequencySpectrum

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OverviewOverview

• Radio Frequencies

• RF Bands and Management

• RF Propagation

• Mixing of Frequencies

• Modulation

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Electromagnetic Frequencies

Electromagnetic Frequencies

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• Electromagnetic spectrum Radio frequencies Visible light and

Infrared Ultraviolet X-rays Gamma rays

• RF has the longest wavelength

• Gamma rays have the shortest

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RF and Visible LightRF and Visible Light

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Radio Frequencies

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Frequency and Wavelength

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>>

Frequency TermsFrequency 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

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Electromagnetic Waves - 1

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

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Electromagnetic Waves - 2

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

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RF Bands and ManagementRF Bands and Management

• Radio frequency bands

• Radio frequency management

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Radio Frequency Bands

Radio Frequency Bands

Designation Abbreviation Frequency Wavelength

Very Low Frequency VLF 9 kHz - 30 kHz 33 km – 10 km

Low Frequency LF 30 kHz - 300 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 - 300 MHz 10 m – 1 m

Ultra High Frequency UHF 300 MHz - 3 GHz 1 m - 100 mm

Super High Freq SHF 3 GHz - 30 GHz 100 mm – 10 mm

Extremely High Freq EHF 30 GHz - 300 GHz10 mm – 1 mm MComm-Ch2 - 10>>

Marine Radio FrequenciesMarine 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

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Electronics by FrequencyElectronics by Frequency

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LORAN & DGPS 100 kHz ground waveNAV-TEX 518 kHz ground waveAM 535 to 1700 kHz

Marine MF 2 to 3 MHz ground wave Voice Guard 2182.0 kHz emergency and calling DSC Guard 2187.5 kHz emergency and calling

Marine HF 4 to 27.5 MHz sky waveTV 2 to 6 54 to 88 MHzFM 88 to 108 MHzCommercial Air 108 to 137 MHz Guard 121.5 MHz emergency

Marine VHF 156 to 158 MHz line of sight Voice Guard (#16) 156.800 MHz emergency and calling DSC Guard (#70) 156.525 MHz emergency and callingWeather 162.40 to 162.55 MHzTV 7 to 13 174 to 216 MHzMilitary Air 225 to 400 MHz Guard 243.0 MHz emergencyEPIRB 406.028 MHzTV 14 to 69 470 to 638 MHzCell Phones 824 to 894 MHzGPS L1 1.57542 GHz 1575.42 MHz>>

RF ManagementRF 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

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Spectrum AllocationSpectrum Allocation

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RF PropagationRF Propagation

• Radio Line-of-Sight

• Ground Wave

• Sky Wave

• Skip Zone

• Ionosphere Layers

• Propagation Software

• Signal Reliability

• Rules of ThumbMComm-Ch2 - 15>>

Radio Line-of-SightRadio 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

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Ground WavesGround Waves

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

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Ionosphere LayersIonosphere 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

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Escaping Sky WavesEscaping Sky Waves

• RF over 50 MHz “escapes”• Ideal between Earth and satellites

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Sky WavesSky Waves

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

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Refraction vs Frequency

Refraction vs Frequency

• Refraction decreases as frequency increases

• At “Critical Frequency” radio wave “escapes”

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Skip ZoneSkip Zone

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

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Sky Waves - 2Sky Waves - 2

• Refraction from “E” or “F” Layer Only one combined “F” layer at night

• One Hop and Two Hop propagation

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Space AttenuationSpace Attenuation

• Strength of signal is inversely proportional to square of the distance from transmitter

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Propagation SoftwarePropagation 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

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Propagation ModelsPropagation 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

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VOACAP input – ASAPS output

VOACAP input – ASAPS output

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Signal ReliabilitySignal 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

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Rules of ThumbRules of Thumb

1. If you can hear them, they can hear you2. MF (2 to 3 MHz) – Ground wave propagation

Day: at least 50 miles and most probably 100 nmNight: out to 200 miles or more

3. 4 to 8 MHzDay: 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 MHzDay: 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-Ch2 - 29>>

Mixing of FrequenciesMixing of Frequencies

• Inputs: two frequencies• Outputs

Two original frequencies Difference Sum

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10 kHz

100 kHz

10 kHz

100 kHz

90 kHz

110 kHz

Mixer

1 kHz

(Audio)

10 MHz

(RF)

10.000 MHz (RF)

1 kHz (Audio)

10.001 MHz (RF)

9.999 MHz (RF)

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ModulationModulation

• Continuous Wave (CW)

• Amplitude Modulation Full Carrier Double Sideband (AM) Suppressed Carrier Single Sideband

(SSB) Other variations

• Frequency Modulation (FM)

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Continuous Wave (CW)Continuous Wave (CW)

• First way of encoding the RF carrier Turn the carrier “ON” and “OFF”

Short “dots” and long “dashes” Morse Code

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“K”

Code was: “USPS Marine Electronics”>>

Amplitude Modulation (AM)

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: 9.999 MHz, 10.000 MHz and 10.001 MHz

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Amplitude vs Frequency

Amplitude vs Time>>

Single Sideband (SSB)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: 10.001 MHz (Carrier & Lower Sideband suppressed)

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Amplitude vs Frequency

USB only>>

Other AM VariantsOther AM Variants

• Other variants Suppressed carrier, double

sideband Suppressed carrier, lower

sideband

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Frequency ModulationFrequency Modulation• Details in Chapter 3• Audio Amplitude changes frequency• Audio Frequency changes rate of frequency

swing

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SummarySummary

• 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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