Electronic noise: why EMC compliance is critical for military computers

All electronic systems – from the smart technology in your home to the military-grade systems that support a nation’s national security – emit electromagnetic signals. Because of the sheer volume of this noise, there are controls and standards in place in both the commercial and military domains that ensure the operation of one electronic system does not negatively impact that of another. In this blog we look at the military electronic compatibility standards and how GRiD meets even the most demanding Electromagnetic Compatibility (EMC) requirements.   

Controlling and mitigating the effect of electronic systems on one another is known as EMC, and there are standards and regulations in place across all aspects of life. From the electronics in your home that make life more convenient or fun, to national infrastructure that supports the functioning of day-to-day life, if it is liable to emit electromagnetic disturbance, it will need to be designed with a consideration of nearby electronics in mind.

These standards are often rooted in law – for example the rules surrounding telecommunications interference – and serve to ensure that a piece of equipment does not disturb other systems, and that it is immune to a certain degree against interference expected in the environment in which it will operate.

EMC compliance and testing is therefore essential for the safe operation of all electronics, and particularly for military systems that are mission critical and cannot be vulnerable to this type of interference.

As a result, EMC certification is now a major requirement for most military projects, but what are the standards that govern this, and how do they differ between countries?

GRiDCASE 2507 in Anechoic Chamber being EMC Tested


The UK approach – DEF STAN 59-411

Equipment used by the UK Ministry of Defence adheres to strict Defence Standards – often shortened to DEF STAN – which have been developed by the Directorate of Standardisation (DSTAN). In the case of EMC requirements, this is DEF STAN 59-411.

This standard sets out the electromagnetic environmental requirements for equipment used by UK armed forces and is one of the strictest in the world. It mandates a satisfactory level of susceptibility that a system can have to other electronics within a certain area, as well as an acceptable level of emissions that it can transmit.

DEF STAN 59-411 is subdivided into Land, Air and Sea classes depending on where the system is going to be used. When an acquisition is made, it will be outlined what level of DEF STAN 59-411 certification is required, and a supplier will then have to test its system to certain requirements to demonstrate that it is compatible to the necessary level.

Air and Sea have different sub-divisions of these standards based on whether the system will be used above or below decks for the latter, and dependent on the type of aircraft for the former.

Land, meanwhile, is further separated into classes D through to A. Electronic systems certified to Land Class D will be able to operate normally over 100m from an antenna, while Land Class A covers personnel-worn systems that must be able to operate within 2m of one.

The portability of infantry- and special forces-carried systems and the probability of them being near emitting antennas makes them more challenging to certify to EMC standards.

Land Class C is the most common for military systems in this subdivision, and dictates that systems must be able to operate within 15-100m from an antenna. Land Class B, meanwhile, must be able to operate between 2m and 15m – a challenging requirement for electronics manufacturers and one that many cannot meet!

During testing, a metal test cell surrounds the system being tested to stop external emissions (similar to a Faraday cage), and an antenna is then used to detect ‘noise’ within the cell. It measures emissions coming out of all aspects of the system, and a system must emit below a certain level to meet the criteria of that classification.

The US and elsewhere: MIL-STD-461

The US Department of Defense, meanwhile, has published Military Standard 461 (MIL-STD-461) for electromagnetic interference/compatibility, which is used by the US armed forces and has additionally been adopted by other allied forces worldwide.

MIL-STD-461 defines the test limits for the control of electromagnetic interference (EMI) of subsystems, while MIL-STD-464 (currently published in the ‘D’ version) is similar but covers platform-level characteristics.

Introduced in 1967, the latest version of the standard is MIL-STD-461G, which was published in 2015.

The full DoD document for MIL-STD-461G is found here and for MIL-STD-464D here.

The standard is broken down by the platforms that each subdivision applies to. Surface ships and submarines each have their own test limits, for example, as do aircraft across each of the services’ aircraft fleets. Ground systems for each of the services have different specifications, as do space systems including launchers.

The test limits for land systems that fall under ‘MIL-STD-461: Ground, Army Limits’ are the most equivalent to the UK’s Land Class C specification, and are approximately 95% the same.

The GRiD approach

It is worth noting that despite the commonality, UK DEF-STAN 59-411 standards are traditionally more rigorous than the US DoD’s MIL-STD-461, and as such, GRiD chooses to make sure that it certifies to DEF STAN requirements as standard.

More often than not, GRiD is asked to qualify its products to Land Class C, but occasionally we are asked to meet more stringent standards. In 2021, our GRiDCASE 2507 7” tablet was qualified to DEF-STAN 59-411 Land Class A, which is a significant achievement for this type of product.

Read more: The GRiDCASE 2507 is EMC Qualified!

When considering the EMC challenges associated with computer systems, tablets are often easier to build and certify to strict EMC standards because they are not hinged like a laptop is. A hinged screen requires extra wiring and cabling that introduces more electromagnetic noise and conducts emissions, and there is also a full keyboard to contend with.

As previously mentioned, Land Class C is the most common sub-division of DEF-STAN 59-411, and the most customer-requested standard for GRiD’s products.

However, in 2023 GRiD achieved a significant milestone with the successful Land Class B certification for the GRiDCASE 1513 13.3” laptop. This certification is notably more difficult to achieve than Land Class C, and is unique for a military-grade laptop. This is testament to our engineering know-how as a rugged laptop OEM, and a huge achievement for the company.

Moreover, it is worth noting that GRiD only uses UKAS-accredited independent test houses to carry out EMC testing, which ensures that qualification is carried out thoroughly and the standard is fully followed. There is no room for error with this approach, and GRiD is confident that its products very closely follow the requirements of the standards and are a safe bet for customers.

All aspects of certification are critical to GRiD and its family of rugged laptops and tablets, and EMC is no exception. Only by independently certifying to the highest of standards and leveraging highly-experienced UK engineers can GRiD ensure that it delivers best-in-class performance to its customers.


If you would like to discuss EMC in more detail, please get in touch on +44 (0)1628 810 230 or drop an email to sales@griduk.com.