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Topic 3 Intro to RF Enabling Objectives

Topic 3 Intro to RF Enabling Objectives 3.1 DEFINE the terms: Hertz, Cycle, Frequency, Wavelength, Bandwidth, and EIRP and how they apply in the electromagnetic spectrum. 3.2 DISCUSS antenna theory, including directivity, polarization, LOS, and antenna types.

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Topic 3 Intro to RF Enabling Objectives

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  1. Topic 3 Intro to RF Enabling Objectives 3.1 DEFINE the terms: Hertz, Cycle, Frequency, Wavelength, Bandwidth, and EIRP and how they apply in the electromagnetic spectrum. 3.2 DISCUSS antenna theory, including directivity, polarization, LOS, and antenna types. 3.3 DESCRIBE some of the advantages and disadvantages of circuits operating in the HF through EHF bands. 3.4 DESCRIBE types of communication links and multiple access methods. 3.5 DEFINE modulation terms, including AM, FM, ASK, FSK, and PSK. 3.6 LIST atmospheric layers and DEFINE ionization, reflection, refraction, diffraction, doppler, ducting, and atmospheric variations. 3.7 DISCUSS wave transmission properties.

  2. Signals Environment

  3. Year(s) • 1895-1901 Marconi invents radio (called “wireless”) • 1945 Arthur Clarke describes concept of using • a geo-stationary satellite for communications • -1957 USSR Launches Sputnik • -1967 INTELSAT I (24 voice channels)/DSCS I • -1976 GAPFILLER satcom (used by US Navy) • -1990-present UHF Follow-On (UFO), • DSCS III SHF, MILSTAR EHF, Satcom • and many more……. BACKGROUND

  4. Clarke Orbit - 1945 • Concept conceived by science fiction author Arthur C. Clarke • Envisioned three artificial satellites in a 24-hour (GEO) orbit, giving complete television and microwave coverage to the entire planet

  5. Moon Relay - 1954 • U.S. Navy experiment - world's first operational space communications system, called Communication by Moon Relay (CMR) was used between 1959 and 1963 to link Hawaii and Washington, DC.

  6. Echo 1 Satellite - 1960 • NASA spacecraft - 100-ft. diameter balloon made of aluminized polyester placed in 800-900 nautical mile orbit • Radio waves could be reflected off of the smooth aluminum surface

  7. Radio – communication between two or more points, using electromagnetic waves as the transmission medium SATCOM DOWNLINK SATCOM UPLINK Non-Satellite Communications

  8. THE ELECTROMAGNETIC SPECTRUM ELF VLF LF MF HF VHF UHF SHF EHF IR VL UV Xrays Gamma rays etc. Radio Portion Low Freq High Wavelength Long Short Frequency x Wavelength = Speed of Light

  9. 1 wavelength RADIO WAVES Higher Frequency Lower Frequency 1 wavelength Frequency x Wavelength = Speed of Light

  10. Wave Classifications Transverse Wave Longitudinal Wave Disturbance Disturbance Travel Travel

  11. Basic Sine Wave

  12. Frequency/Period 1 Second 4 Hz

  13. e.g., 2 Hz e.g., 1 Hz ~ 300,000 Km ~ 186,400 Mi ~ 150,000 Km   Amplitude Amplitude 0 .25 .50 .75 1.0 1.25 1.50 Time 0 .25 .50 .75 1.0 1.25 1.50 Time Radio Frequency Terms • Wavelength - Distance between points of corresponding phase of two consecutive cycles of a wave. The distance a wave will travel (propagate) in one complete cycle.  = v / f = Propagation velocity / Frequency

  14. Velocity (C) 1 Second 186,000 Miles 300,000,000 Meters

  15. Relationships 1 C ƒ T ƒ λ ƒ= Frequency C = Velocity T = Period λ = Wavelength

  16. 50 MHz Bandwidth Power 10.475 GHz 10.500 GHz 10.525 GHz Center Freq Frequency Radio Frequency Related Terms • Bandwidth - The width, in Hertz, of the satellite signal or channel. • Narrowband • Wideband • Throughput - The number of bits per second of information passing through a data communication system. Also referred to as data rate.  MaximumThroughput is directly proportional to BW

  17. Bandwidth A signal is centered at 15kHz with a total BW of 6kHz. How does it look in the spectrum? 0 kHz 5 kHz 10 kHz 15 kHz 20 kHz 25 kHz 30 kHz

  18. Antennas

  19. Directivity • Unidirectional - Receives or radiates efficiently in one direction only. • Bi-directional - Receives or radiates efficiently in two directions, 180 degrees apart. • Omnidirectional - Receives or radiates efficiently in all directions 360 degrees.

  20. Unidirectional Antenna

  21. Omnidirectional

  22. Polarization • Vertical • Horizontal • Right Hand Circular • Left Hand Circular How the wave propagates in relation to the Earth.

  23. Line Of Sight

  24. Antenna Types • There are vast number of antenna types used for many different purposes. • Whip • Rhombic • Log-Periodic • Parabolic • Arrays

  25. Whip Parabolic Rhombic LPA Yagi

  26. FRD-10/WullenweberCircular Disposed Antenna Array(CDAA)

  27. SIMPLEX One Direction Only (e.g., GBS) POINT B POINT A HALF DUPLEX Two Directions, One At A Time POINT B POINT A FULL DUPLEX Two Directions Simultaneously (like a telephone) POINT B POINT A Types of Comm Links

  28. SATCOM Related Terms • EIRP - Effective Isotropic Radiated Power • Power that a theoretical isotropic (point) radiator would have to put out in all directions to equal the actual power transmitted in one direction by a directional antenna. • Multiple Access • Use of the allocated spectrum (channel / transponder) by multiple users: • FDMA - Frequency Division Multiple Access • TDMA - Time Division Multiple Access • SSMA - Spread Spectrum Multiple Access

  29. Some of the Bandwidth, all of the time Power FDMA B A C BW Frequency FRAME TDMA Power All of the Bandwidth some of the time A B C BW BW BW T1 T2 T3 Time C B C A All of the Bandwidth all of the time - DSSS (CDMA) - Frequency hopping SSMA A A Freq B A B C C B Time SATCOM Related TermsTypes of Multiple Access

  30. Modulation Terms • Modulating Wave • Intelligence converted to an electromagnetic waveform (such as: voice converted from AF to an EM waveform after entering a microphone or telephone) • Carrier Wave (ƒc) • A Radio Frequency Wave with Constant Amplitude, Frequency & Phase • Modulated (complex) Wave • The resultant wave after the modulation process.

  31. AM • The process of varying the Amplitude of the Carrier Wave in Accordance with the Amplitude of the Modulating Wave

  32. DSB

  33. SSB

  34. ISB

  35. FM

  36. ASK

  37. FSK

  38. PSK

  39. UHF Advantages: Workhorse of Naval Satcom, Very Widespread, Can use small, lightweight equipment Disadvantages: Low Data Rates, Very crowded, Susceptible to jamming UHF 300-3000MHZ Utility SHF EHF 30-300GHZ 3-30GHZ Capacity Survivability EHF SHF Advantages: LDR:Anti-Jam, Anti-Scint, LPD/LPI MDR: better data rates, less survivability Disadvantages: LDR slow, Not as widespread as UHF Cloud bursts can interfere w/ xmsn Advantages: High Data Rate, Joint interoperability Disadvantages: Not widespread, DSCS Crowded, CWSP cost Small antennae make ships “disadvantaged users”

  40. Frequency Band UHF SHF EHF Military Utility 225 MHz - 3 GHz 3 Ghz-30 GHz 30 GHz - 300 GHz BW Resources Used Low Moderate High Survivability Low Moderate High Comm-On-The-Move High Moderate Moderate Terminal Cost Low Moderate High Maintenance Cost Low Moderate High Technical Complexity Moderate Moderate High General Frequency Band Attributes

  41. Atmospheric Layers

  42. Radio Phenomena • IONIZATION • REFLECTION • REFRACTION • DIFFRACTION • DOPPLER

  43. Ducting

  44. Atmospheric Variations • Sun Spots • Regular - those which are more or less regular and occur in cycles. • Irregular - Variations which are unpredictable and that can drastically affect communications capabilities without any advance warning.

  45. Sun Spot Cycles

  46. Wave Transmission • Ground Wave • Surface Wave • Space Wave • Sky Wave

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