Presentation on theme: "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."— Presentation transcript:
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.
BACKGROUND Year(s) Marconi invents radio (called “wireless”) Arthur Clarke describes concept of using a geo-stationary satellite for communications USSR Launches Sputnik INTELSAT I (24 voice channels)/DSCS I GAPFILLER satcom (used by US Navy) present UHF Follow-On (UFO), DSCS III SHF, MILSTAR EHF, Satcom and many more…….
Clarke Orbit 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
Moon Relay 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.
Echo 1 Satellite NASA spacecraft ft. diameter balloon made of aluminized polyester placed in nautical mile orbit Radio waves could be reflected off of the smooth aluminum surface
SATCOM UPLINK SATCOM DOWNLINK Non-Satellite Communications Radio – communication between two or more points, using electromagnetic waves as the transmission medium
ELF VLF LF MF HF VHF UHF SHF EHF IR VL UV Xrays Gamma rays etc. THE ELECTROMAGNETIC SPECTRUM FreqHighLow Frequency x Wavelength = Speed of Light Wavelength ShortLong Radio Portion
RADIO WAVES 1 wavelength Higher Frequency Lower Frequency Frequency x Wavelength = Speed of Light
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. 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 e.g., 1 Hz ~ 300,000 Km ~ 186,400 Mi Amplitude Time e.g., 2 Hz ~ 150,000 Km Amplitude Time Radio Frequency Terms
Velocity (C) 186,000 Miles 300,000,000 Meters 1 Second
Relationships 1 Tƒ C λƒ ƒ = Frequency C = Velocity T = Period λ = Wavelength
Bandwidth - The width, in Hertz, of the satellite signal or channel. Bandwidth - The width, in Hertz, of the satellite signal or channel. NarrowbandNarrowband WidebandWideband Power 50 MHz Bandwidth Frequency GHz GHz GHz Center Freq Throughput - The number of bits per second of information passing through a data communication system. Also referred to as data rate. Maximum Throughput is directly proportional to BW Radio Frequency Related Terms
Bandwidth A signal is centered at 15kHz with a total BW of 6kHz. How does it look in the spectrum? 0kHz5kHz10kHz15kHz20kHz25kHz30kHz
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.
Polarization Vertical Horizontal Right Hand Circular Left Hand Circular How the wave propagates in relation to the Earth.
Line Of Sight
Antenna Types There are vast number of antenna types used for many different purposes. –Whip –Rhombic –Log-Periodic –Parabolic –Arrays
SIMPLEX One Direction Only (e.g., GBS) POINT A POINT B HALF DUPLEX Two Directions, One At A Time POINT A POINT B POINT A POINT B FULL DUPLEX Two Directions Simultaneously (like a telephone) Types of Comm Links
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
FDMA Power A B C Frequency Some of the Bandwidth, all of the time BW Time TDMA Power A BC T1T1 T2T2 T3T3 BW All of the Bandwidth some of the time FRAME SSMA Time Freq A B C A B C A B C A B C All of the Bandwidth all of the time - DSSS (CDMA) - Frequency hopping SATCOM Related Terms Types of Multiple Access
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.
AM The process of varying the Amplitude of the Carrier Wave in Accordance with the Amplitude of the Modulating Wave
UHF MHZ Utility SHF 3-30GHZ Capacity EHF GHZ Survivability UHF Advantages: Workhorse of Naval Satcom, Very Widespread, Can use small, lightweight equipment Disadvantages: Low Data Rates, Very crowded, Susceptible to jamming SHF EHF Advantages: High Data Rate, Joint interoperability Disadvantages: Not widespread, DSCS Crowded, CWSP cost Small antennae make ships “disadvantaged users” 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
General Frequency Band Attributes
Radio Phenomena IONIZATION REFLECTION REFRACTION DIFFRACTION DOPPLER
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.