MIL-DTL-27599D
4.6.18 EMI shielding (see 3.20).
4.6.18.1 EMI shielding (from 100 to 1,000 MHz only). The EMI shielding effectiveness of mated
connectors with EMI backshells shall be measured in a triaxial radio frequency leakage fixture as shown
on figure 8. The EMI leakage from the conductor inside the connector in the same inner coaxial line into
the outer coaxial line shall be measured at the frequencies specified in table III within a frequency
accuracy of ± 5 percent. The level of detected signal power shall be indicated by a tunable radio
frequency field intensity meter isolated from the test circuit by a 3 to 10 dB pad. Care shall be taken to
ensure that the signal is a result of EMI leakage from within the mated connector and not due to a faulty
termination inside the fixture. All terminations inside the fixture, whether to the EMI backshells or
between internal conductors, shall have a leakage at least 10 dB less than the test requirements. The
signal source shall be set to the desired frequency. The signal shall be fed through a 3 to 10 dB isolation
pad to a parallel circuit consisting of a coaxial switch (DPDT) so connected that the signal can be
manually or electronically fed alternately to the fixture and to a variable 100 dB reference attenuator. The
attenuator shall be adjustable in 1 dB steps and calibrated to ± 3 dB.
a. The inserts may be removed from the connectors under test to accommodate a center
conductor of suitable geometry to provide a good 50-ohm impedance match with the inside
diameter of the mated connector shells and EMI backshells. Tapered transition may be used
to provide a means of changing diameters without introducing significant discontinuities in the
line. The maximum VSWR in the inner coaxial line shall be 1.5. The outer shell of the test
fixture shall be so constructed as to provide a good 50-ohm impedance match with the
outside diameter of the mated connector shells, coupling ring, and EMI backshells. The
maximum VSWR of the outer coaxial line shall be 1.5.
b. A sliding circumferential short shall be positioned behind the connector on the signal input
end of the fixture to provide for turning the outer coaxial line for maximum output at each test
frequency. The allowable travel of this short shall be greater than ½ wave length at the
lowest test frequency of 1.5 meters minimum for 100 MHz. The inner coaxial line shall be
terminated in a fixed 50-ohm load impedance behind the connector at the output end of the
fixture.
c.
The connectors used to couple together the various elements of the test system shall be of a
low-leakage type which have a nominal impedance of 50 ohms, a VSWR of less than 1.5, and
a minimum leakage attenuation of 100 dB. The output impedance of the signal source and
the input impedance of the detector shall be nominally 50 ohms with a maximum VSWR of
1.5. The input and output VSWR of the standard attenuator shall be less than 1.5 in the 20 to
100 dB range.
d. The relative signal level in the variable attenuator shall be equaled to the signal level through
the leakage fixture by adjusting the attenuator. The signal loss in the fixture can then be read
from the setting on the variable attenuator.
4.6.19 Contact plating thickness (see 3.23). Contact plating thickness shall be measured in
accordance with ASTM B488.
4.6.20 Contact engagement and separating force (see 3.24). Connectors shall be mounted in a
suitable fixture for applying gradually increasing loads for the engagement and separation of the specified
SAE-AS31971 test pins and in accordance with test procedure EIA 364-37. The test pins shall be
inserted a minimum of .7L (see SAE-AS39029). A maximum diameter test pin shall be inserted and
removed from each socket contact. The engagement force shall be measured during insertion. A
minimum diameter test pin shall be inserted and removed from each socket contact and the separation
force shall be measured during removal.
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