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MIL STD

Switching-Mode Power Supply Switching-Mode Power Supplies (SMPS) are used extensively in many electronic applications. Many manufacturers offer MIL-STD-461 compliant solutions, as well as Commercial Off-The-Shelf (COTS) solutions for military applications. SMPS offer many advantages when compared to Linear Power Supplies. The primary advantage of an SMPS is that it offers power conversion and regulation at 100% efficiency – albeit, given ideal components. All power loss is due to less than ideal components and the power loss in the control circuitry. Other advantages of the SMPS are smaller size and therefore less weight. SMPS have switching frequencies that range from 50 kHz to 1 MHz.

Although commercial off the shelf (COTS) products are not typically designed for use in military electromagnetic environments (EME), manufacturers are attempting to integrate them into other products for use in military EME. This quickly growing trend has increased for several reasons; the most compelling are cost-savings and miniaturization and modularization of COTS products. While this trend has been a welcome development for manufacturers of military solutions with integrated COTS products, demonstrating their compliance with the stringent DoD military standards is fraught with challenges.

To specify MIL-STD-461E and MIL-STD-461F CE101 in voltage conducted emissions limits, variations of power source impedances in test facilities must be controlled. Since imposing this requirement is not practical, it is more reasonable to specify a current conducted emissions limit. Below are other reasons why the limit is specified as current rather than voltage:

CE101 in MIL-STD-461F applies only to Navy submarines, Navy aircraft and Army aircraft. CE101 is not required for Air Force aircraft, Air Force ground, Army ground, or Navy ground platforms.

The intent of CE101 is as follows:

The Federal Aviation Administration (FAA) and the European Aviation Safety Agency (EASA) will accept RTCA/DO-160 commercial aircraft equipment test reports from accredited and non-accredited labs.


Regardless of a lab’s accreditation status, the FAA and the EASA require that test reports adhere to their standards of acceptability, and that the accompanying documentation meet all of their requirements. If this is not the case, the FAA and/or the EASA will require that the sub-standard submissions be revised/augmented before any further review, which will delay approval.

A client recently inquired as to whether it would be possible to see a reduction in radiated spurious emission levels on Spread Spectrum Clock (SSC) fundamental frequency and harmonics using Peak Detectors during MIL-STD-461F testing of a COTS product, when previous FCC Part 15 testing of the COTS product proved compliance using Quasi-Peak Detectors. We are pleased to share our response: If COTS with SSC products with Part 15 compliant fundamental frequencies and harmonics are tested to MIL-STD-461F using required Peak Detectors, the spectral peaks of their fundamental frequencies and harmonics should comply with MIL-STD-461F, provided the SSC timing parameters are properly configured. A properly configured SSC would produce lower spectral peaks of the fundamental frequency and harmonics in the SSC mode than the spectral peaks of the fundamental frequency and harmonics in the non-SSC mode by levels that are dependent on the manufacturer of the SSC, modulating waveform profile, modulation rate used to modulate the fundamental frequency clock frequency in the SSC mode, spreading rate style used (down, center or up) as depicted using (Δ) in Figure 1 below:

 

Rhein Tech Laboratories, Inc. is pleased to share a response we provided to a client’s recent request for an explanation of the measurement detector requirements in MIL-STD-461F product testing. MIL-STD-461F requires peak detectors for all product testing. MIL-STD-461F, paragraph A.5.1.1 (5.1.1) Units of frequency domain measurements states: “All frequency domain limits are expressed in terms of equivalent Root Mean Square (RMS) value of a sine wave as would be indicated by the output of a measurement receiver using peak envelope detection.”

Recently, a client contacted Rhein Tech Laboratories, Inc. about requirements for Electromagnetic Interference Test Procedure (EMITP) in MIL-STD-461F product testing. We are pleased to share our response below. The MIL-STD 461F standard requires that a product be tested and evaluated, taking into consideration its unique functional characteristics and operational environment

On January 31, 2012, Rhein Tech Laboratories, Inc. hosted the EMC Society Washington DC/Northern Virginia Chapter meeting at our Herndon, Virginia office.     The meeting started with dinner followed by two educational and information presentations by Mr. Mitch Lazarus, of and Desmond Fraser, president of Rhein Tech Laboratories, Inc. Mr. Lazarus’ presentation, entitled “Millimeter Wave Radiation,” provided insight on the FCC’s view on the upper edges of measurable RF energy.   His presentation can be found here:

How does one calculate a radar’s maximum range (Rmax), if it is a C band with 2.5MW peak transmit power (Pt), operating at 5.8GHz with an antenna gain (G) = 40dBi and an effective temperature (Te) = 290K, and its pulse width (?) = 0.25 ?sec? The radar’s minimum threshold is (SNRmin)= 25dB, and we assume its Radar Cross Section (RCS) (?) = 0.15m2 and its Noise Figure (F) = 3 dB. To determine the radar’s maximum range (Rmax) we must first calculate its bandwidth (B) and wavelength (?) using equation 1 and equation 2 below.

Submersible cell phones are advertised on the Internet, but what is the radiated power of a cell phone submersed in water compared to when it radiates in free space?  What should its current be with the antenna submersed in water in order to maintain the same radiated power as in free space? The cellular phone in this example has the following parameters, ?r = 81, ? = 0, ? = ?0, and uses a 0.008 m (8 mm) long shot dipole antenna that carries 2.5 A current and radiates at 1850 MHz. In order to prove that any change in radiated power is as a result of a change in the medium’s permittivity in which the dipole antenna radiates, and that the permittivity affects its intrinsic impedance, we must first show that the dipole antenna is a Hertzian dipole. To do so, we must calculate the dipole antenna’s wavelength in air and compare it to its physical length, in order to determine if it is electrically shorter than the wavelength of the cell phone’s operating frequency.  We will use Equation 1 below.

RTCA/DO-160F has incorporated significant changes to Section 21, Emission of Radio Frequency Energy, from the test methods and procedures used in RTCA/DO-160E. A brief synopsis of the changes is summarized below. Frequency Range Changes RTCA/DO-160F has eliminated the use of the 41” Rod Antenna. The radiated RF emissions frequency range requirements have been changed from 2 MHz to 6 GHz to 100 MHz to 6 GHz. The conducted RF emissions frequency range has been expanded to an end frequency of 152 MHz. New Equipment Category A new equipment category, Category P, has also been added to Section 21 of RTCA/DO-160F. Category P is defined as: “Equipment and associated wiring located in areas close to high frequency, VHF or GPS radio receiver antennas, or where the aircraft structure provides little shielding.” The test limits for Category P are shown below. Figure 1 is the Conducted RF Emissions Limit for power lines and interconnecting bundles and Figure 2 is the Radiated RF Emissions Limit.

A major contributor to EMI is the airframe itself. It is made of aluminum and can behave much like a satellite dish compounding the effects on both internal and external EMI by concentrating the transient signals and sending the interference into nearby equipment. Commercial electronic and electrical equipment is regulated by the Federal Communications Commission (FCC), which defines allowable emissions and susceptibility levels. Military equipment is regulated by Military Standards (MIL-STD), specifically MIL-STD-461 and MIL-STD-462. MIL-STD-461 defines allowable emission levels, both conducted and radiated, and allowable susceptibilities, both conducted and radiated.

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