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How Military Testing Standards are Changing

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Cost Effective Tests Using ATE, DFT and BIST

by Louis Y. Ungar at APEX on February 18, 2007 

The first Radio Frequency Interference issues were encountered by the US military some time prior to World War I when a radio was first installed on a vehicle. However, very little is known about early efforts to address RFI problems until the early 1930s. The first military specification was published by US Army Signal Corps in 1934 as SCL-49. Very soon it became apparent SCL-49 was inadequate. In 1942 it was superseded by specification 71-1303, that addressed shielding, the use of filters, by-pass capacitors, resistor-suppressors, bonding, grounding and proper wire routing. Later a joint Army-Navy standard JAN-I-225 was issued then in 1947.

The subsequent succession of military EMC specifications closely follows the evolution of our electro-technology. Initially, military specification limits for radio frequency interference were established to protect the minimum usable field strength on board vehicles for land, sea, and air. As more sensitive equipment was developed, susceptibility limits were established. With the space age came the concept of electromagnetic compatibility within small platform systems and also between platforms. As a consequence, the equipment and system specifications became more general to include all types of electrical and electronic equipment that require application of EMC techniques during the design, development, production, installation, and operational states.

In early days each major military agency imposed its own electromagnetic interference specification in the procurement of electronic systems or subsystems. Air Force used MIL-I-6181 and MIL-I-26600, the Navy used MIL-I-16910, and the Army used MIL-I-11748 and MIL-E-55301(EL). Soon it became very obvious that there was a need to limit the number of these different specifications and the generation of one unified standard to serve all government and military agencies. That gave birth to the idea of a combined Specification for all branches; the first such attempt was the government publication of MIL-STD-826 in January 1964.

Soon after MIL-STD-461A was issued in August 1968, as a result, approximately 20 basic and subsidiary specifications were superseded. The 461 document focused on requirements and the 462 standard prescribed measurement methodologies. It was accepted by the joint services and was also used by many other countries. Since the 1970s EMC personnel of the US Army, Navy and Air Force have periodically met and upgraded MIL-STD-461 and 462. The latest revision (1999) consolidated the two standards into one standard: MIL-STD-461E. This latest edition is an "interface" standard of requirements to provide reasonable assurance (during development) that a system, subsystem or equipment will be compatible with its anticipated electromagnetic environment.

Some of the most significant changes in MIL-STD-461/D/E and the older revisions are as follows:

• Deletion of Broadband emission tests.
• 6 dB, measurement bandwidths.
• Susceptibility scan times specified.
• ANSI C63.14 is referenced for definitions.

Military EMC Standards have evolved, over the past few decades dramatically from a simple beginning to very detailed standards to keep pace with the "Technology Explosion" and the resultant complex electromagnetic environment. The MIL-STD-461/2 D as well as the new MIL-STD-461E were developed (1990 to 1999) by approximately 15 U.S. government and industry experts to meet the ever changing electromagnetic environment. However, the development of EMC specifications is never finished since the technology requiring compatibility constantly changes.

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