## Presentation on theme: "Radio Frequency Spectrum"— Presentation transcript:

Chapter 2 Radio Frequency Spectrum PowerPoint slides by Stf/C Harl Porter, SN Marine Electronics Rear Commander for Electro-Mechanical Systems is R/C Gene Danko, SN

Overview Radio Frequencies RF Bands and Management RF Propagation
Mixing of Frequencies Modulation Major sections in this chapter >>

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 Figure on right is equivalent to Text fig 2-1 Radio frequencies are at the low-energy end of the electromagnetic spectrum and have the longest wavelength (the general equation can be found in the text as “speed of light = frequency x wavelength” – see slide 5) Wavelength is shown on the left side of the figure Audio is NOT in the electromagnetic spectrum (as this graphics suggests); it consists of air pressure waves. The frequency range is shown here for comparison. Radio bands above UHF are SHF and EHF (not shown) Radio band below LF is VLF (not shown) >>

RF and Visible Light Radio Frequencies
Top illustration expands the radio bands Some electromagnetic spectrum illustrations do NOT show Cosmic rays, found at the top of the spectrum, or electrical waves shown at the bottom Lower illustrations expands visible light, which is just one small component of the spectrum The chart at the top is shown in increasing units of frequency; the chart at the bottom is in increasing wavelength (i.e., increasing frequency would go from right to left). Explain this to the students and explain that this is why the rainbow colors are reversed from one to the other. >>

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) Illustration is Text figure 2-2 Point out one cycle and wavelength Symbols used “λ” is wavelength “f” is frequency MHz is MegaHertz (term is explained on the next slide) Quiz the students: if the frequency is 300 MHz, what is the wavelength? Answer: 1 meter. You can think of other examples. >>

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 Note that kilohertz used a small “k” (as in kHz), other abbreviations use a capital letter (e.g. MHz and GHz) >>

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 Called an electromagnetic field, as it has both magnetic and electric components. Note how they are at right angles to each other. >>

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 Space attenuation can be over 100 db for long RF signals, but if transmitters are powerful enough, antenna gain is high enough, and receivers are sensitive enough, one can detect a usable RF signal. Deep space probes are an extreme example; they broadcast ~25 watts, but are detected across distances of millions of kilometers >>

RF Bands and Management

Radio Frequency Bands Designation Abbreviation Frequency Wavelength
Very Low Frequency VLF 9 kHz - 30 kHz 33 km – 10 km Low Frequency LF 30 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 UHF 300 MHz - 3 GHz 1 m mm Super High Freq SHF 3 GHz - 30 GHz 100 mm – 10 mm Extremely High Freq EHF 30 GHz GHz 10 mm – 1 mm Text table 2-3. Note that VLF goes down to only 9 kHz; other bands are all 3 to 30. These are same bands shown on the title slide for this chapter. The white dashed box indicates the bands of interest for terrestrial maritime voice/data communications. The red dashed box indicates the band of interest for satellite voice/data communications. >>

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 Text table 2-4 These are the three bands used for Marine Radio Communications. USB is Upper Side Band, which will be covered in chapter 7. Shown are the voice calling and distress frequencies and DSC calling and distress frequencies. At this time there are no DSC hailing and emergency frequencies in the HF band, only voice hailing and distress frequencies. The VHF-FM Marine band is from 156 to 162 MHz Currently, one can transmit voice only on to MHz The VHF weather band is to MHz >>

Electronics by Frequency
This table gives Marine Electronic frequencies and in right column how they are normally propagated (ground wave, sky wave or Line-of-Sight). The table is arranged lowest frequency or longest wavelength (at top), to highest frequency (at bottom). Also shown are other common transmitters to show where they are in the RF Spectrum. The three Marine Radio bands are pointed out. >>

RF Management Internationally In United States
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 International organization for Frequency (or RF) Management is ITU, the U.S. is a signatory and has agreed to abide by their decisions. In the United States, frequencies are managed (allocated) by NTIA for the Federal Government, which includes our Armed Forces; and by FCC for all other (non-government) users. CFR (Code of Federal Regulations), Title 47 (Telecommunications), Part 80 ([Radio] Stations in Maritime Service) are the Rules and Regulations for Marine Radios. >>

Spectrum Allocation Don’t try to read big chart, it shows U.S Frequency allocation, by type of service, from 9 kHz up to 300 GHz. Circled portion is 12 to 18 MHz, and is the expanded section turned vertically Two Maritime Mobile frequency blocks are in this range >>

RF Propagation Radio Line-of-Sight Ground Wave Sky Wave Skip Zone
Ionosphere Layers Propagation Software Signal Reliability Rules of Thumb Topics in this section >>

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 Text fig 2-5 Propagation mode for Marine VHF-FM and VHF TV (54 to 216 MHz), UHF TV (470 to 638 MHz) and Cell Phones (824 to 894 MHz). Sailboats can talk farther as their VHF antennas are at the top of their masts. If there is a temperature inversion (warmer air aloft than at surface), one gets extended range beyond formula prediction. Formula constant decreases with frequency; varies down to 1.24 at 10 GHz and down to 1.17 for visible light. >>

Ground Waves Ground Wave follows Earth's surface
MF (2 to 3 MHz) uses this mode Longer range at night Text fig 2-6 Portion of energy follows earth’s surface Propagation mode used by MF and lower HF. Also used by Loran (100 kHz), NAVTEX (518 kHz), and AM Commercial Radio (535 to 1700 kHz) >>

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 Color equivalent to fig 2-7 Illustrate four Ionization layer during daylight hours and one combined F layer at night. The “D” layer (lowest) attenuates MF and lower HF frequencies during the day. Useful refraction is from “E” and “F” layers. At night the two “F” layers (F1 and F2) combine into one layer which accounts for longer radio ranges at night. >>

Escaping Sky Waves RF over 50 MHz “escapes”
Ideal between Earth and satellites Text fig 2-8 Higher frequencies (over approx 50 MHz) are not refracted by the Ionosphere. They will penetrate the ionosphere layers and will not be reflected back to earth. The frequencies are also propagated via Line-of-Sight mode. Over 50 MHz frequencies are ideal for communications between satellites and earth. The GPS L1 frequency is GHz and INMARSAT satellites use frequencies between and GHz. >>

Sky Waves Refracted by Ionosphere
HF and VHF up to 50 MHz uses this mode Amount of refraction is a function of frequency Text fig 2-9 Will speak to Ionosphere layers in a couple of slides. During the day there are four layers; at night there is only one. HF (3 to 30 MHz) day and night; and MF (2 to 3 MHz) during darkness are refracted in the ionosphere back to earth. Amount of refraction is a function of frequency. Ray “2” is lower in frequency, hence more refraction; Ray “3” is higher in frequency, hence takes longer in ionosphere to be refracted back to earth. >>

Refraction vs Frequency
Refraction decreases as frequency increases At “Critical Frequency” radio wave “escapes” Illustrates points made on previous slides. Lower frequency is refracted more and returns to earth at shorter distance. Use higher HF frequencies to talk greater distances. See Rules of Thumb 3 and 4 later VHF and higher frequencies are shown “escaping” >>

Skip Zone Note Ground Wave coverage Note Sky Wave coverage
No coverage gap is “Skip Zone” Color equivalent to Text fig 2-10 Excellent illustration of Skip Zone Frequency “(1)” is either too high or at too high an angle to be refracted back to earth and will “escape” Lower frequencies, less than “(2)” will not be refracted back to earth Frequencies increase from “(2)” to “(3)” which illustrates going higher in frequency results in longer range Frequencies over “(3)” will not be refracted back to earth >>

Sky Waves - 2 Refraction from “E” or “F” Layer
Only one combined “F” layer at night One Hop and Two Hop propagation Text fig 2-11 is a daytime “picture” that shows both “E” and “F” layer; the “E” layer only exists during daylight hours. Illustrates one and two hop RF wave propagation. >>

Space Attenuation Strength of signal is inversely proportional to square of the distance from transmitter Illustrates space attenuation as a function of distance. Sky wave is illustrated, also applies to line-of-sight. Explain the inverse square law to the students: if the distance is doubled, the apparent signal strength is one quarter, etc. >>

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 Propagation Software has made frequency selection much easier. The Pactor HF Data modem, covered in Chapter 5, comes with frequency selection (propagation prediction) software. There are several Propagation Prediction software programs. VOACAP is based on IONCAP (Ionospheric Communications Analysis and Prediction) written by the US Department of Commerce in the late 70s. Voice of America assumed maintenance of IONCAP in the early 1990s. Now it is maintained by Greg Hand, a HF Scientist who worked for NTIA/ITS in Boulder CO, and is free. ASAPS (Advanced Stand-Alone Prediction System) was developed by the Australian government and costs about \$275. >>

Propagation Models Inputs Output 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 The four major inputs to the propagations models are as shown. We are most interested in FOT (suggested frequency) and predicted path probability outputs. Frequencies over MUF will go past intended destination. Frequencies under LUF will not reach intended destination. Graphics display on next slide. >>

VOACAP input – ASAPS output
Simple input for VOACAP One of several output screens from ASAPS >>

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 Text fig 2-12 Frequency propagation can be reduced to two charts. Author unknown – First published in USPS Marine Radio Communications (ME102), 2003 Edition. Accounts for Day vs Night and Distance and Time of Year (two seasons). Does not account for 28-day sun cycle or 11-year sunspot cycle; averages are assumed in these charts. >>

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 Stf/C Harl Porter’s Rules of Thumb Good summary of MF and HF radio propagation >>

Mixing of Frequencies Inputs: two frequencies Outputs
Two original frequencies Difference Sum 10 kHz 100 kHz MHz (RF) 1 kHz (Audio) 1 kHz (Audio) 10 MHz (RF) Mixer circuits have two inputs and four outputs. The outputs are the two input frequencies and their sums and differences. The example is one audio frequency and one RF frequency. The resulting three RF frequencies are amplitude modulated. 10 kHz 100 kHz 90 kHz 9.999 MHz (RF) Mixer 110 kHz MHz (RF) >>

Modulation Continuous Wave (CW) Amplitude Modulation
Full Carrier Double Sideband (AM) Suppressed Carrier Single Sideband (SSB) Other variations Frequency Modulation (FM) Topics covered in this section >>

Code was: “USPS Marine Electronics”
Continuous Wave (CW) First way of encoding the RF carrier Turn the carrier “ON” and “OFF” Short “dots” and long “dashes” Morse Code On left is Morse code “K” (long, short, long or dash, dot, dash). Y-axis (up & down) is amplitude, X-axis is time (left to right). On right is Morse code for letters and numbers. Sound is “USPS Marine Electronics” “USPS” in Morse code is: dit, dit, dah, space, dit, dit, dit, space, dit dah, dah, dit, space, dit, dit, dit. “Dit” is how a dot is spoken. “Dah” is how a dash is spoken, it is 3 “dits” long. The space between letters is 3 “dahs” long. “K” Code was: “USPS Marine Electronics” >>

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 Amplitude vs Time Amplitude vs Frequency Text fig 2-13 (on left) and Text fig 2-14 (on right). AM was the first way that voice was imposed on to a RF carrier. On left is Amplitude (Y-axis) vs Time (X-axis) Top 3rd is the RF carrier Middle 3rd is the modulating audio frequency (single tone) Bottom 3rd is the resulting AM modulated RF carrier. On right is Amplitude (Y-axis) vs Frequency (X-axis). fc is original RF frequency. fm is modulating audio frequency (a single frequency tone). Note that the two sidebands (fc – fm and fc + fm) are half the amplitude of fc, and are identical. Bandwidth required is 6 kHz. Power is dissipated in carrier and two sidebands. >>

Amplitude vs Frequency
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) Amplitude vs Frequency USB only Text fig 2-15 RF carrier and lower sideband have been suppressed. Like in AM, the modulating audio frequency has been eliminated. Single Sideband, Upper Sideband (USB) is the modulation used in Marine MF and HF radios. Bandwidth required is 3 kHz and all the power is in the one single sideband. >>

Other AM Variants Other variants Suppressed carrier, double sideband
Suppressed carrier, lower sideband Suppressed carrier, double sideband Bandwidth required is 6 kHz No power wasted in RF carrier Suppressed carrier, lower sideband (LSB) Bandwidth required is 3 kHz Same power efficiency as USB Full carrier, independent sidebands Bandwidth required is 6 kHz (same as AM) Used for point to point fixed communications Note that fm1 is different than fm2 Two different voice channels with no increase in transmitted power >>

Frequency Modulation Details in Chapter 3
Audio Amplitude changes frequency Audio Frequency changes rate of frequency swing Text fig 2-16 Top 3rd is modulating signal (a single tone). Middle 3rd is FM modulated carrier as Amplitude vs Time. Bottom 3rd is FM modulated carrier as Frequency vs Time. Note how FM modulated signal is of constant amplitude. Modulating volume changes carrier frequency. Modulating frequency is rate of frequency change across RF carrier frequency. Marine VHF-FM requires 10 kHz bandwidth as deviation is limited to +/- 5 kHz. In broadcast FM deviation is +/- 75 kHz (Bandwidth of 150 kHz). >>

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 No notes >>