Mil. Std. 461F and DO-160 test accessories including loop antennas, feed-thru capacitors, audio, isolation and pulse transformers, coupling networks, resistive networks and loads, precision resistors and spark gaps.

Historical Note

The AT-205/URM-6 Loop Sensor described in Test Method RE01 of MIL-STD-462 is one of the antennas designed for use with the Navy AN/URM-6B and Stoddart NM-10A receivers. These were the low frequency EMI meters that, in 1948, initiated the emphasis on EMI by the military departments and created the technical discipline we now know as Electromagnetic Compatibility.

Description

The Solar Type 7334-1 Loop Antenna has been designed as a substitute for the AT-205/URM-6 antenna and is a replacement for Eaton Model 94607-1. It uses 36 turns of wire on a 5.25" (13.3 cm) diameter form enclosed in an electrostatic shield as described in paragraph 5.2.1 of MIL-STD-461A.

The Type 7334-1 is equipped with an epoxy-glass base plate which serves as a spacer to enable the user to place the loop at exactly 7 cm from the face of the item under test as required by test procedure RE01 of MIL-STD-462.

Application

Connection to the loop is through a BNC connector which enables coaxial cabling to the EMI receiver. The loop is supplied with a correction factor graph showing the values in dB which must be added to the reading of a 50 ohm EMI meter to obtain answers in either dB/μV/m or dB/pT. The correction factor decreases as frequency increases from 30 Hz up to approximately 15 KHz, where the factor levels off and remains relatively constant up to 5 MHz.

The Type 7334-1 Loop Antenna is required by Test Method RE01 in Parts 2 through 6 of MIL-STD-461C and RE101 of MIL-STD-461D.These portions of the specification require magnetic field emission tests of cables, equipments, systems and sub-systems installed in, or used in, all phases of military vehicles, ships, submarines, aircraft (including helicopters), spacecraft, or ground-based operations.

TEST METHODS RE01 and RE101

The Type 7334-1 Loop Antenna is positioned 7 cm from the face of the equipment under test with the plane of the loop parallel to the equipment face. The best position to begin with is opposite or near a joint or seam. The associated EMI meter is then scanned over the range 30 Hz to 100 KHz searching for emissions. At the frequencies where emissions are found, the loop antenna is moved about the surface seeking the strongest emission level. When a strong signal is detected, the loop is oriented on its axis for a maximum reading. This procedure is repeated for all surfaces of the equipment under test. Although the specification is not clear on the point, it appears to indicate that all six sides (including the bottom) of an equipment must be tested in this manner. When testing cables, the loop antenna is placed 7 cm from the cable with the plane of the loop parallel to the cable. The non-metallic base plate of the Type 7334-1 Loop Antenna provides a convenient means for establishing the correct 7 cm distance.

Figure 1

Description

The loop antenna used for generating radiated magnetic fields is fully described in Figure 1A of MIL-STD-461A. It consists of ten turns of number 16 A.W.G. wire on an insulated form 4.72" (12 cm) in diameter. The winding is placed on the form in a position which allows the form to be used as a spacer to place the winding 5 cm from the face of the item under test as required by test method RS01 of MIL-STD-462.

The Type 7429-1 Loop Antenna has been designed to the exact requirements of the specification. The loop winding is placed on a durable plastic form and is equipped with banana jack style terminals for connection to the test setup. The loop is not shielded.

Application

In a practical RS01 test setup, the loop antenna is supplied with the required current versus frequency by the Solar Model 6550-1 Power Sweep Generator. The current is measured with a voltmeter connected across the Solar Type 7144-1.0 Precision Resistor which is connected in series between the loop and the generator.

The a.c. current in the Type 7429-1 Loop Antenna to generate the magnetic field intensity required by test method RS01 at 5 cm from the loop winding is depicted on a graph supplied with the loop. The required current varies from a few microamperes to about 5 amperes as frequency is adjusted over the range 30Hz to 50 KHz.

Figure 1

Figure 2

Description

This antenna was designed as a replacement for Eaton 94608-1. It is similar to Stoddart 91117-2, 30-inch diameter loop, supplied with AN/URM-6B and NM-10A EMI receivers. In addition to operating as a receiving antenna, the Type 9130-1 Loop Antenna is capable of carrying ten amperes in test setups for generating magnetic fields.

Although the antenna it is replacing is circular (30 inches in diameter), the Type 9130-1 Loop Antenna is almost square, 28.5" x 29.75" with 6.31" radius at each corner (12.4 cm x 75.5 cm with 16 cm radius). This larger area results in an improved pickup factor. The loop is wound with larger wire than the original, so that it can carry more current in the transmitting mode. Fitted with Type N connector.

APPLICATION

As a receiving antenna the Type 9130-1 is more sensitive than the original 30-inch diameter loops. The graph below shows the comparison when connected to a receiver with 50 ohm input impedance.

When used to generate magnetic fields, the Type 9130-1 Loop Antenna is capable of carrying up to ten amperes through its eleven turns, making 110-ampere turns. With one ampere flowing through the winding, the magnetic field generated is over 277.5 volts-per-meter at one meter distance from the plane of the loop and 12.6 volts-per-meter at three meters distance. With ten amperes flowing, the field intensity is 126 volts-per-meter at three meters distance.

The Type 9130-1 Loop Antenna can be used for receiving radiated magnetic fields as well as generating a stipulated magnetic field at a specified distance. The generated magnetic field is a function of the current flowing in the loop and the distance from the loop to the point of measurement.

Figure 2 indicates how the current through the loop varies with distance and magnetic field levels. For 18 dB increase in field intensity at a given current, the distance is divided by two. Conversely, at a given current as the distance is doubled, the field intensity becomes 18 dB less. As the current is multiplied by ten, the field intensity increases by 20 dB. In other words, the field intensity change in dB is twenty times the log of the change in current at a given distance.

Note that the Type 9130-1 Loop Antenna is wound with wire suitable for carrying up to ten amperes. For higher currents, apply the current for short intervals. Allow the winding to cool off.

Figure 1

Description

Test Method RS101 of MIL-STD-461D requires radiated magnetic fields over the frequency range 30 Hz to 100 KHz to determine the susceptibility or immunity of the equipment under test (EUT). Two loop antennas are required for compliance with the requirements.The radiating loop is 12 cm in diameter and the sensing loop (used for calibration) is 4 cm in diameter. The Type 9230-1 Radiating Loop has been designed so that the Type 9229-1 Loop Sensor can be attached at the required 5 cm distance.

APPLICATION

The test method requires calibration of the radiated energy at 1.0 KHz prior to the test. Calibration of the Type 9230-1 Radiating Loop is accomplished by coupling the Type 9229-1 Loop Sensor to it at a distance of 5 cm. The arrangement is indicated in Fig. 1 on the next page.With a known current flowing in the radiating loop, the magnetic field can be measured.

Two graphs are supplied with the loops to make life easier for the test engineer. Fig. 2 shows a typical correction factor curve for the Type 9229-1 Loop Sensor. Fig. 3 indicates the amount of current flowing through the Type 9230-1 Radiating Loop to generate the required magnetic field, in dB/pT.

The current level to produce 110 dB/pT at 1.0 KHz is 3.0 mA. An accurately calibrated EMI meter or spectrum analyzer will measure this as 42 dB/μV. Adding the correction factor of 68 dB/pT/μV from Fig. 2 equals 110 dB/pT as required by the specification.

In those instances where the spectrum analyzer does not have sufficient sensitivity, the calibration can be accomplished just as well at a higher current level. For example, using 300 mA, the measurement would be 82 dB. Subtracting 40 dB from this answer and adding the 68 dB factor will equal 110 dB/pT/μV.

Another approach to the calibration and the measurement depends on the accuracy of the EMI receiver. Simply subtract the sensor correction factor in dB/pT/μV (Fig. 2) from the desired magnetic field level in dB/pT (Fig. 3). Then adjust the current until the EMI meter reads this value in dB above one microvolt.

Example: For a field of 110 dB/pT at 1.0 KHz, subtract 68 dB (Fig. 2) from this to obtain 42 dB. This value in dB above one microvolt on the EMI meter is equal to 126 μV as indicated in RS101.

A typical calibration test setup is shown in Fig. 4a. For current levels below 25 mA, it is feasible to use a standard laboratory signal generator. For higher current levels, the signal must be amplified (Fig. 4b). Both methods show a 0.1 ohm precision resistor (Type 9817-0.1) and a digital voltmeter for measuring the current.

USEFUL ANCILLARY DEVICE

Type Type 9817-0.1 Precision Resistor, 0.1 ohm, 1%. For measuring current flowing in the radiating loop.

Figure 1

Description

The Type 6512-106R Feed-Thru Capacitor is a highly reliable and ruggedly constructed unit for general use in screen rooms or other environments. The 3.375" square case with four husky mounting inserts lends itself to convenient installation with a minimum of effort. The 1⁄4-28 UNF threaded feed-thru stud will easily accommodate power currents in excess of 100 amperes without heating or voltage loss.

The capacitance value is 10 μ
F ±10%. The Type 6512-106R voltage rating is 600 volts d.c., 275 volts at 60 Hz, and 250 volts at 400 Hz. Low dissipation factor, high temperature rating, high insulation resistance, doubly rated dielectric strength, and long life characterize this versatile device. To satisfy safety requirements, a bleeder resistance is included in the Type 6512- 106R Feed-Thru Capacitor which serves to discharge the capacitor when the applied voltage is removed.

APPLICATION

The Type 6512-106R Feed-Thru Capacitor was especially designed for use in RFI/EMI test setups as required by MIL-STD-461/462 and other specifications. In this application it provides a low r.f. impedance across the power source so that EMI currents produced by a test sample can be accurately measured with current probes.
The 10 μF feed-thru capacitor can also be used as a power line filter installed in the wall of a shielded enclosure or equipment cabinet. The capacitor provides adequate insertion loss without suffering the power current saturation limitation of conventional filters which employ toroidal inductors.

Specifications

Current Rating: Limited by the heat of the 1⁄4-28 threaded terminal stud. Easily handles 100 amperes of power current. Can be used for currents in excess of 200 amperes intermittent duty.

Temperature: Will operate at full rated voltage from -55C to 100C. To +125C with 50% voltage derating.

Dissipation Factor: Less than 1% at 25C.

Dielectric Strength: Will withstand the application of twice rated voltage at 25C for a period not to exceed two minutes.

Insulation Resistance: At rated voltage or less for a period two minutes, the insulation resistance will exceed 2500 megohms at 25C. However, insulation in excess of 500,000 ohms cannot be measured due to the bleeder resistor built into the unit.

Bleeder Resistance: An internal bleeder resistor of 500,000 ohms is included as specified in SAE document ARP-936.

Life Test: Will withstand the application of 600 volts at 85C for 250 hour.

Construction: Extended foil coaxial winding protected with a thin mylar film. Hermetically sealed with ceramic to metal seals.

Figure 1

Type 7525-1 Series Capacitor, 0.1 μF, BNC connectors

Solar Type 7525-1 is 0.1 microfarad, fitted with BNC connectors. The reactance of this series capacitor reduces the power frequency voltage to a safe limit so that the output circuit of the generator will not be damaged. At 500 KHz, the r.f. signal is not greatly attenuated.

At frequencies above 20 or 30 MHz, the connections from the banana jacks to the test sample will create discontinuities that cannot be removed from the setup. It is recommended that the wires from the banana jacks be less than one inch long to minimize VSWR anomalies.

DIMENSIONS 2.0" (51 mm) X 2.5" (63.5 mm) plus mounting flanges x 1.25" (31.25 mm) high.

Type 9133-1 Three Phase Delta Capacitor, 10 μF

Type 9133-1 Three Phase Capacitor Assembly for Line-to-Line Capacitance in Delta- Connected Power Systems.

This handy device contains three capacitors, ten microfarads each, connected to provide capacitance from phase A to B, A to C, and B to C. The capacitors are rated at 270 volts A.C. As a safety feature, each capacitor is paralleled with a 500K resistor to prevent a voltage charge from remaining on the assembly after power is disconnected. It is fitted with1/4-28 feedthru studs to facilitate making connection from three phase power to a three phase load up to 100 amperes. The Type 6512-106R capacitor can be used for the neutral in wye-connected power systems.

Dimensions: 3.5" x 6.0""x 3.75" high. (89 mm x 152 mm x 95 mm)

Type 9146-1 Three Phase Wye Capacitor, 10 μF

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Description

The transformer is capable of handing up to 200 watts of audio power into its primary over the frequency range 30 Hz to 250 KHz. The turns ratio provides a two-to-one step down to the special secondary winding.The secondary will handle up to fifty amperes of a.c. or d.c. without saturating the transformer.

Another secondary winding is connected to a pair of binding posts suitable for connecting to a.c. voltmeter as directed by the applicable EMI specifications. This winding serves to isolate the voltmeter from power ground. Neither the primary nor the secondary windings are connected to the end bells of the core. The transformer may be used as a 4-ohm primary and 1-ohm secondary or 2.4-ohm primary and 0.6-ohm secondary or 2-ohm primary and 0.5-ohm secondary.

APPLICATION

The Type 6220-1A Audio Isolation Transformer was especially designed for screen room use in making conducted audio frequency susceptibility tests as required by MIL-STD-461/462 and other EMI specifications.

The transformer may also be used as a pickup device to measure low frequency EMI currents at lower levels than conventional current probes.

In addition, its secondary may be used as an isolating inductor in the power line during transient susceptibility tests. (See Application Note AN622001.)

Specifications

Additional Models

Type 6220-2 100 amperes high current transformer.

Type 6220-4 50 amperes 4 KV transient voltage HV transformer.

Type 9707-1 10 amperes low current transformer.