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Spectrum and Electromagnetics 101
This section contains background and basic educational information on Spectrum Supportability (SS) and electromagnetic environmental effects (E3) issues, some introductory technical material on each and the importance of considering each early in the development and acquisition of systems. These resources provide acquisition professionals an overview of the technical aspects of spectrum supportability and E3 considerations in military weapons system procurement.
Electromagnetic Spectrum Management: Planning, coordinating, and managing use of
the electromagnetic spectrum through operational, engineering, and administrative
procedures. [From: Department of Defense Dictionary of Military and Associated Terms, (August 2018)]
E3 Testing: E3 can adversely affect the operational effectiveness of military forces, equipment, systems, and platforms. Today's increasingly complex military EM environment is congested and this is coupled with a reduction of spectrum allocation for exclusive military use. The mix of DoD-developed and commercial-off-the-shelf (COTS) electronic equipment increases the importance of the need for effectively managing E3 and spectrum usage in the battle space. It is the responsibility of the program manager (PM) to ensure, and the responsibility of the Developmental and Operational Test Agencies (D&OTA) to validate, the readiness of systems to be fielded into this environment. Historically, failure to verify equipment/platform EMC in the item's intended operational electromagnetic environment have caused costly program delays and reduced operational effectiveness. [excerpt from DAG Guidebook]
* Super Low Frequency (SLF) Ultra-Low Frequency (ULF) Very-Low Frequency (VLF) Low Frequency (LF) Medium Frequency (MF) High Frequency (HF) Very-High Frequency (VHF) Ultra-High Frequency (UHF)
Super-High Frequency (SHF) Extremely-High Frequency (EHF)
The types of electromagnetic radiation are broadly classified into the following classes:
The decibel (dB) is a logarithmic unit that indicates the ratio of a physical quantity (usually power or intensity) relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities. The decibel is often used to express power or amplitude ratios (gains), in preference to arithmetic ratios or percentages. One advantage is that the total decibel gain of a series of components (e.g., amplifiers) can be calculated simply by summing the decibel gains of the individual components. Similarly, in telecommunications, decibels denote signal gain or loss from a transmitter to a receiver through some medium (free space, waveguide, coax, fiber optics, etc.) using a link budget. The decibel unit can also be combined with a suffix to create an absolute unit of electric power. For example, it can be combined with "m" for "milliwatt" to produce the "dBm". 0 dBm equals one milliwatt, and 1 dBm is one decibel greater (about 1.259 mW).
The following table describes some of the
various modulation types with the principle advantages, disadvantages and uses.
Spread Spectrum Communications Techniques:
A means of communicating by purposely spreading the spectrum (frequency extent or bandwidth) of the communication signal well beyond the bandwidth of the unspread bandwidth. Spread spectrum signals are typically transmitted by electromagnetic waves in free space with usage in both no military and military systems.
Motivation for using spread spectrum signals is based on the following facts:
There are four generic types of spread spectrum signals:
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