MIL-STD-1377 Effectiveness of Cable, Connector and Weapon Enclosure Shielding and Filters
As an industry leader in shielding effectiveness testing, Keystone Compliance has the knowledge and capabilities to meet any MIL-STD-1377 testing needs. From the creation of the test plan to the issuance of the test report, our experts provide guidance every step of the way.
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Request a Quote to speak to an expert and start the path towards achieving MIL-STD-1377 shielding effectiveness testing. The remainder of this document provides an overview of the MIL-STD-1377 testing standard.
The official title is MIL-STD-1377 effectiveness of cable, connector and weapon enclosure shielding and filters in precluding hazards of electromagnetic radiation to ordnance. Essentially, this standard is intended to provide a weapon developer or designer with shielding and filter effectiveness test methods for determining whether the particular weapon design requirements of MIL-P-24014 have been properly implemented.
The scope of MIL-STD-1377 shielding effectiveness tests is not intended to be a substitute for full-scale electromagnetic hazards evaluation tests of the weapon system, but rather an aid in developing a weapon system with a high probability of successfully passing such environmental tests.
MIL-1377 covers the methods of shielding effectiveness of weapon enclosures, cables, and cable connectors over the frequency ranges of from 100 kilohertz (kHz) to 30 megahertz (MHz) and from 1000 MHz to 10 gigahertz (GHz).
The shielding effectiveness test methods are conducted at two separate frequency ranges because of hardware limitations. It is unnecessary to measure shielding effectiveness between 30 MHz and 1000 MHz because of the Navy’s limited use of these frequencies and because experience has indicated that shielding deficiencies in this range will probably appear in either of the two measured frequency ranges.
The upper frequency for the test methods may be increased to 40 GHz when applicable. This standard also covers the methods of measuring the filtering effectiveness of radio frequency (RF) suppression devices (filters) for weapon firing circuits over the frequency range of from 100 kHz to 10 GHz.
To gain a better understanding of the EMC test requirements of this standard, it is important to know the definitions of some of the key words and phrases. A weapon enclosure is the metal shell surrounding a weapon circuit, such as the weapon skin.
The weapon cable is any wiring outside of the weapon enclosure designed to be connected to circuits inside the enclosure. Surface transfer impedance is the ratio of the magnitudes of the longitudinal voltage drop on the outer surface of the shield to the cur- rent on the inside of the shield.
Testing to MIL-1377 shielding valuation requires a number of various pieces of equipment. The list below is not all inclusive, but it does provide an overview of the most common equipment needed.
The signal source shall be any RF signal generator or power oscillator with a current output capability compatible with the ammeter and voltmeter. Any shielded RF current measuring device which can measure the center conductor current of a coaxial cable over the desired frequency range shall be used. Such a device can be constructed from a small metal box and an RF panel ammeter.
The ammeter, mounted inside the box, is connected to the center conductors of two bulkhead connectors mounted on opposite sides of the box. small screen-shielded window in front of the box is used for viewing the meter. The sensitivity of the ammeter shall be compatible with the signal generator output current capability.
It is generally necessary to construct an adapter to link the signal source and ammeter to the test cable. This can be constructed by placing the appropriate connectors on opposite sides of a small metal box and joining the proper center conductors inside. If a multiconductor cable is to be tested, the selection of the conductor(s) to be connected to the signal source is arbitrary.
One end of the test cable shall be terminated with a short that provides shield integrity. An RF voltage measuring device or balanced or near balanced input design shall be wed. The voltmeter probe should be fitted with balanced probe leads, each approximately 3 inches in length. The voltmeter shall be coordinated with the signal generator such that it is capable of measuring RF voltages as small as 1 millivolt per ampere of signal generator output current capability.
To avoid direct coupling to the voltmeter probe, the circuit from the signal source to the cable under test should be shielded. The effectiveness of this shield should be greater than that of the cable under test. This can be determined by shorting the cable adapter and measuring the voltage and the center conducting current with the signal generator on. The surface transfer impedance (STI) calculated from this arrangement shall be at least 20 decibels (db) below the STI of the test cable when calculated.