This section contains background and basic educational information on Spectrum Supportability 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.
To develop a system that will operate compatibly in its fielded environment, the program management staff must address spectrum supportability and E3 throughout the system life cycle. Program managers must ensure that EMC and Spectrum Supportability are designed into the system. Numerous DoD agencies and organizations can assist the program office with E3 matters.
E3: The impact of the electromagnetic environment upon the operational capability of military forces, equipment, systems, and platforms. It encompasses all electromagnetic disciplines, including electromagnetic compatibility/electromagnetic interference (EMC/EMI); electromagnetic vulnerability; electromagnetic pulse (EMP); electronic protection (EP); hazards of electromagnetic radiation to personnel (HERP), ordnance (HERO), and volatile materials (HERF); and natural phenomena effects of lightning and p-static (precipitation static). [The following definitions are from: Department of Defense Dictionary of Military and Associated Terms, March 23, 1994 (as amended through Feb. 10, 1999)]
Spectrum Management: Planning, coordinating, and managing joint use of the electromagnetic spectrum through operational, engineering, and administrative procedures, with the objective of enabling electronic equipment to perform their functions in the intended environment without causing or suffering unacceptable interference. [The following definitions are from: Department of Defense Dictionary of Military and Associated Terms, March 23, 1994 (as amended through Feb. 10, 1999)]
Objective for E3 Control - The objective of establishing E3 control requirements in the acquisition process is to ensure that DoD equipment, subsystems, and systems are designed to be self-compatible and operate compatibly in the operational electromagnetic environment. To be effective, the program manager should establish E3 control requirements early in the acquisition process to ensure compatibility with co-located equipment, subsystems, and equipment, and with the applicable external electromagnetic environment. [excerpt from DAG Guidebook]
E3 Testing - - E3 can adversely affect the operational effectiveness of military forces, equipment, systems, and platforms. Additionally, today's complex military operational environment is characterized by an increasingly congested electromagnetic spectrum coupled with a reduction of spectrum allocated for exclusive military use. The mix of DoD-developed and commercial-off-the-shelf electronic equipment increases the importance of effectively managing E3 and spectrum usage in the battle space. It is the responsibility of the program manager to ensure, and the responsibility of the Developmental and Operational Test Agencies to validate, the readiness of systems to be fielded into this environment. Historically, failure to verify equipment/platform electromagnetic compatibility in the item's intended operational electromagnetic environment have caused costly program delays and reduced operational effectiveness. [excerpt from DAG Guidebook]
ELECTROMAGNETICS - The Spectrum
| ELF |
Radio Spectrum |
Microwaves |
Terahertz |
Infrared |
Visible |
Ultraviolet |
X-Rays |
Gamma Rays |
| 3-30 Hz |
SLF: 30-300 Hz |
0.3-300 GHz |
300 GHz-3 THz |
Far Infrared: 300 GHz-30 THz |
400-790 THz |
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30 PHz-30 EHz |
1019 Hz and above |
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ULF: 300-3 kHz |
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Mid-Infrared: 30-120 THz |
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VLF: 3-30 kHz |
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Near-Infrared: 120-400 THz |
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LF: 30-300 kHz |
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MF: 300-3000 kHz |
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HF: 3-30 MHz |
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VHF: 30-300 MHz |
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UHF: 300-3000 MHz |
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SHF: 3-30 GHz |
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EHF: 30-300 GHz |
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* Scientists are looking to apply Terahertz technology in the armed forces, where high frequency waves might be directed at enemy troops to incapacitate their electronic equipment.
What is a decibel or dB?
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).
Antenna Basics. https://acc.dau.mil/CommunityBrowser.aspx?id=704895
The following table describes the various modulation types with the principle advantages, disadvantages and uses.
| Kind |
Advantages |
Disadvantages |
Uses |
| Amplitude Modulation - double side band plus carrier (AM) |
Simplifies receiver; preserves the waveform of message |
Doubles bandwidth occupancy; Requires extra signal power. |
Radio broadcasting, telephony, telegraphy, telemetering. |
| Single-sideband, suppressed carrier (SSB) |
Saves bandwidth occupancy; Conserves signal power |
Unable to handle relatively low frequencies; adds inherent delay; waveform of wanted message is not preserved. |
Long distance telephony and telegraphy over land and submarine cables. |
| Phase Discrimination Multiplexing (applicable to many channels). |
Conserves bandwidth and signal power |
Sensitive to transmission impairments. |
Minor |
| Angle Modulation - Narrow band |
Constant signal power |
Extra bandwidth occupancy |
Telecommunications, particularly broad-band carrier and TV over microwave radio ready systems. |
| Wide band |
Reduces noise in exchange for extra bandwidth occupancy; constant signal power; channel-grabbing property |
Bandwidth occupancy; sensitive to some forms of transmission impairment; signal power must be adequate to override wideband noise. |
Telecommunications generally, including such fields as telegraphy, telephony, radio broadcasting, telemetering, mobile communications for military and peacetime services, navigational aids, maritime beacons, and meteorological aids. |
| Pulse Amplitude Modulation (PAM) |
Permits multiplexing channels by time division. |
Sensitive to some forms of transmission impairment. |
Radio, radar, telegraphy, telephony, telemetering, time-multiplexed sampled data systems, computers, switching systems |
| Pulse Duration Modulation (PDM) |
Permits multiplexing channels by time division; reduces noise in exchange for extra bandwidth occupancy; constant signal power |
Extra bandwidth occupancy; pulses vary in position. |
Microwave radio relay systems, telemetering |
| Pulse Position Modulation (PPM) |
Permits multiplexing channels by time division; reduces noise in exchange for extra bandwidth occupancy; constant signal power; saves signal power as compared to PDM. |
Extra bandwidth occupancy; pulses vary in position. |
Microwave radio relay systems, telemetering |
| Pulse Code Modulation (PCM) |
Permits multiplexing channels by time division; in exchange for extra bandwidth occupancy, tolerates considerable noise and serious transmission impairments, and may be repeated again and again without significant distortion; constant signal power. |
Extra bandwidth occupancy; transmits digital instead of analog signals, thereby introducing quantization noise if the receiver delivers analog signals. |
Multiplex telephony and telegraphy, TV, data processing, combined transmission and switching systems, telemetering. |
| Digital Modulation - Phase Shift Keying (PSK) |
Excellent performance for binary and quaternary systems; good bandwidth efficiency for M-ary systems |
Poorer performance for M-ary systems when M > 4 |
Voice, data, and video over satellite and terrestrial channels. |
| Digital Modulation - Frequency Shift Keying (FSK) |
Simple receiver structure; excellent performance for M-ary systems when M > 4 |
Poor performance of binary systems; bandwidth occupancy grows as M/log2 M in M-ary system |
Voice, data, and video over satellite and terrestrial channels. |
| Multiple Modulation |
Many depending upon circumstances; often accomplishes what cannot be done in one step. |
Extra steps usually add extra complexity |
A feature of all but the simplest transmitters and receivers. |
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:
- These systems have the ability to reject intentional and unintentional jamming by interfering signals so that information can be communicated
- Spread Spectrum signals have a low probability of being intercepted or detected since the power in the transmitted wave is "spread" over a large bandwidth or frequency extent
- Since these signals cannot be readily demodulates without knowing the code or cypher, and it's precise timing, message privacy is obtained
- The wide bandwidth of the spread spectrum signals provides tolerance to multipath (reflected waves that take longer to arrive at the receiver than the direct desired signal)
- A high degree of precision in ranging (distance measuring) can be obtained by using one type of spread spectrum signal, with applications to navigation
- Multiple access, or the ability to send many independent signals over the same frequency band.
There are four generic types of spread spectrum signals:
- Direct Sequence (DS) - The carrier of a DS source stays at a fixed frequency. Narrowband information is spread out into a much larger bandwidth using a pseudo-random chip sequence.
- Pseudo noise (PN)
- Frequency Hopping (FHA)
- Linear Frequency Modulation (chirp)
Chirp Modulation: This is an older spread spectrum method that was developed for radar use. The basic idea is to transmit a long rectangular pulse whose carrier frequency is linearly increased from f1 to f2 (f2>f1). The frequency-modulated signal returned from the target passes through a filter in the receiver at a velocity of propagation proportional to frequency. The result is a pulse that is much shorter in time duration than the transmitted pulse with a larger peak power content. Unchirped pulses such as interference or jamming pulses do not "compress" at the receiver, so that this method yields a processing gain or advantage for the chirpped signal.
Time Hopping: Not normally used alone, is a method in which the transmitted pulse occurs in a manner determined by a pseudorandom code which places the pulse in one of n possible positions per frame. If n is sufficiently large, then the pulse is on only 1/n of the time, and again the transmitted pulse has a processing gain against a full frame jamming pulse of equal energy.
Direct Sequence Systems: Direct sequence systems were once the most prevalent method of communicating in spread spectrum communications. Direct sequence modulation is characterized by phase-modulating a sine wave by an unending string of pseudo noise code chips (symbols of much smaller duration than a bit). This unending string is typically based on a pseudo noise code that generates an apparently random sequence of code chips that repeat only after the code period.
JSC E3 Document Library
JSC E3/SS Awareness Training Schedule and Class List
