The ability to operate compatibly with other systems in its intended electromagnetic environment (EME) has become a critical factor in both system acquisition and operational planning. The JSC can provide a complete environmental analysis that includes the use of worldwide frequency assignment databases. Extensive parameter databases, and sophisticated analysis models that can predict when, where, and how interference might occur for terrestrial, air, and space-borne systems.
Cosite EMC
The dependence of modern military operations on electronic systems often means that multiple radiating and receiving equipment must be placed in close proximity, often on the same platform. This placement can lead to cosite electromagnetic interference that degrades system performance. The JSC has leading experts that can prevent and solve cosite problems. They utilize unique capabilities including: specialized equipment parameter databases, sophisticated antenna coupling models, and interference analysis tools designed specifically to predict when cosite interference will occur, so remedial measures can be implemented.
Cosite models are used to evaluate potential high-power, non-linear effects when systems operate in proximity to each other. Cosite analyses consider the following effects:
- Intermodulation
- Harmonics
- Spurious response
- Adjacent signal
- Component/receiver burnout
- Case penetration
- Receiver desensitization
- Typical cosite platforms (Soldier, Airframe, Tower)
Results of analysis include recommendations for ideal placement/location of devices and frequency usage.
Inter-site models are used to assess the impact of C-E equipment on other equipment within its operational environment.
- Similar to cosite EMC but radiating/transmitting and receiving antennas are separated at greater distances and incident interference signals are typically weaker than in the cosite environment.
- Must consider interactions of all RF-dependent devices
- Co-channel and adjacent signal interference are primary concerns
- Effects of terrain, propagation, electromagnetic environment
- Antenna sidelobe and backlobes
- Computer modeling is used to assess myriad potential interactions
- Typical intersite scenarios
- Battlefield
- Test/demonstration
- Interference mitigation techniques
- Device placement/location, frequency management
- Antenna design
Radiation Hazards (RADHAZ)
RF energy in itself can be a hazard. RADHAZ is typically mitigated by separation from the emitter source and these are the typical warning signs posted. There are three classes of RADHAZ that we worry about.
- Hazard of Electromagnetic Radiation to Personnel (HERP): is the danger to personnel from the absorption of electromagnetic energy by the human body. Personnel hazards are associated with the absorption of RF energy above certain power levels in certain frequency bands for certain lengths of time. It is all spelled out in the DoD instruction noted. DoD Instruction 6055.11 defines the allowable amounts in terms of how long personnel may be exposed to RF fields of particular intensities at particular intensities at particular frequencies. You have seen warning signs such as this one posted aboard ships.
- Hazard of Electromagnetic Radiation to Fuel (HERF): is the hazard associated with the possibility of igniting fuel or other volatile materials through RF energy induced arcs or sparks. It takes a certain amount of arc energy to ignite a fuel and modern fuels like JP-5 are much safer than older fuels like JP-4. You can see how that might be a concern aboard an aircraft carrier. Fortunately, there are many operational safeguards against this problem and many of the newer fuels such as JP-5 are much harder to ignite.
- Hazard of Electromagnetic Radiation to Ordnance (HERO): refers to the susceptibility of electroexplosive devices to RF energy. These EEDs or EIDs are used to detonate explosives, launch ejection seats, cut tow cables, etc. Modern communication and radar transmitters can produce high electromagnetic environments that are potentially hazardous to ordnance. These environments can cause premature actuation of the following sensitive, electrically initiated devices.
