MIL-STD-188-125-2: High-Altitude Electromagnetic Pulse Protection For Ground-Based C4I Facilities

MIL-STD-188-125-2 Shielding Effectiveness Compliance Testing

MIL-STD-188-125-2 is a military standard that outlines the requirements for shielding effectiveness testing of electronic components and systems. The standard is designed to evaluate the ability of electronic components and systems to protect against the effects of electromagnetic interference (EMI), which can cause errors in data transmission, degrade system performance, and potentially lead to system failure.

Shielding effectiveness testing, as specified in MIL-STD-188-125-2, is designed to measure the level of protection provided by a component or system’s electromagnetic shielding. The testing procedure involves exposing the component or system to electromagnetic energy in the frequency range of 30 MHz to 1 GHz, and measuring the level of interference that the component or system experiences as a result of the exposure.

The testing procedure specified in MIL-STD-188-125-2 involves the use of an anechoic chamber or a shielded room, as well as specialized test equipment and instrumentation, such as a spectrum analyzer or a network analyzer. The testing procedure must be performed in accordance with the requirements outlined in the standard, including the use of specified test frequencies, test methods, and measurement procedures.

By conducting MIL-STD-188-125-2 shielding effectiveness testing, organizations can ensure that their electronic components and systems are protected against the effects of EMI, and are able to operate effectively and efficiently in demanding electromagnetic environments.

Summary of MIL-STD HEMP Compliance Testing

The MIL-STD-188-125-2 standard evaluates a system’s ability to comply with high-altitude electromagnetic pulse (HEMP) hardening of transportable ground-based systems. These systems have features of time-urgent command, control, communications, computer, and intelligence missions.

Specifically, this is a series with a companion specification of MIL-STD-188-125-1, with the only difference being that this specification addresses only transportable systems. Whereas MIL-STD-188-125-1 addresses fixed facilities. In other words, this addresses the minimum requirements for showing a predetermined performance has been achieved and for verifying installed protection measures provide operationally required HEMP for the completed system.

System examples include, and are not limited to, subscriber terminals and data processing centers, transmitting and receiving communications stations, and relay systems under the assumption that long-haul communications paths, fiber optic links, or other hardened interconnects between systems are provided as required as such in the field.

These relate to transportable systems such as electrical shielding enclosures or fixed rooms in buildings. However, this is as long as the unit fulfills the sole purpose of the specification. The owner will determine if the observed event is mission aborting.

Scope of MIL-STD-188-125-2 Regulatory Compliance

To understand this shielding effectiveness EMC test standard, it is important to understand some of the more commonly used terms. Included in the following paragraphs are some definitions that better explain some of the terminology of this testing.

HEMP Acceptance Testing

Performed on a system, subsystem, or component. These tests are performed to ensure that specified HEMP performance characteristics have been met. HEMP acceptance tests are typically conducted near the conclusion of a hardening production or installation contract.

These tests are for the purpose of demonstrating that at least minimum performance requirements of the HEMP protection measures have been achieved before the unit is accepted by the Government from the contractor.

HEMP Hardness

A quantitative description of the resistance of a system or component to temporary or permanent malfunction or degraded performance induced by HEMP. Furthermore, HEMP hardness is achieved through adhering to appropriate design specifications and is verified by one or more test and analysis techniques.

HEMP Hardness Critical Item (HCI)

An item at any assembly level having performance requirements for the purpose of providing HEMP protection. Nuclear HCIs provide protection from environments produced by a nuclear event or are specially designed to operate under nuclear weapon (device)-derived stresses.


The elements of HEMP protection. A hardness critical assembly is a top-level definable unit of HEMP HCIs and other components, such as mounting hardware and terminal posts, that may not be hardness critical.

A Pulsed Current Injection (PCI)

A test method for measuring the performance of a point of entry protective device on a penetrating conductor. A HEMP threat-relatable transient is injected on the penetrating conductor at a point outside the electromagnetic barrier, and the residual internal transient stress is measured inside the barrier.

Verification Testing

A test conducted for demonstrating that the installed HEMP protection measures provide the required HEMP hardness. These tests are performed after the production and acceptance testing are complete and after the equipment is installed and functioning, to determine if the operating system suffers mission-aborting damage or upset due to simulated HEMP excitations.

Verification is normally a Government-conducted test and is not part of a system production contract.

MIL-STD-188-125 Compliance Test Procedures

The MIL-STD 188-125 test setup is similar to other shielding effectiveness standards, with the determination of the dynamic range and the actual measurement of the signal for the sample in question. If the system involves a weapon enclosure, all internal components need removed such that only the enclosure is being tested.

A benefit of the MIL-STD-188-125-2 DSC system is its improved efficiency in maritime communications. The system provides a more reliable and efficient means of transmitting and receiving information, including position, weather and navigation information, between vessels and shore-based stations. This can help to reduce communication errors and improve the overall safety of maritime operations.

The results of MIL-STD-188-125-2 shielding effectiveness testing provide important information on the electromagnetic compatibility of the component or system under test. This information can be used to evaluate the susceptibility of the component or system to electromagnetic interference, identify areas for improvement, and determine if the component or system meets the desired electromagnetic compatibility requirements.

Expert MIL-STD-188-125-2 Compliance Lab

MIL-STD-188-125-2 shielding effectiveness testing is an essential standard for evaluating the electromagnetic compatibility of components and systems. The standard provides guidelines for the testing procedure, interpretation of results, and reporting of data, and is critical for ensuring that components and systems operate as intended in the presence of electromagnetic energy in military and aerospace applications, as well as in commercial and industrial settings.

Keystone Compliance has the capabilities to test any size enclosure to MIL-STD-188-125-2. We have tested large items such as entire on-site installation buildings and small items that can be easily transported to our lab.

Additionally, Keystone is regarded as one of the best HEMP testing labs in the country. We understand that the need exists for uniform and effective hardening, hardness verification, and hardness maintenance/hardness surveillance of transportable ground-based C4I systems.

Are you ready to partner with Keystone Compliance to determine the shielding effectiveness of your product when tested to the requirements of MIL-STD 188-125-2? Let’s get started!

Diagram of MIL-STD-188-125-2 Testing

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