MIL-DTL-87104C
4.6.2.1.1.4 Test method 3: Swept slotted line. When using the swept slotted line, the VSWR measurements shall
be recorded by an X-Y recorder using 8- by 10-inch graph paper (10 by 10 to the inch). The traces shall be an X-Y
plot of dB/cm versus frequency and shall be plotted with a limit of 1 octave per plot at a minimum sweep rate of
30 seconds per frequency band. If equipment under test exhibits an abrupt change in VSWR, the sweep rate shall be
further slowed to assure that the pen of the X-Y recorder can follow these abrupt changes. The traces shall be
marked at frequency increments of not greater than 0.01 GHz between 0.30 and 0.50 GHz, 0.025 GHz between 0.50
and 5 GHz, 0.05 GHz between 5 and 10 GHz, and 0.10 GHZ above 10 GHz, and labeled at not greater than four
times the increments specified. In addition, the plot shall have a nomograph that converts dB/cm to VSWR, and shall
identify the test sample, the test date, the serial number, the technician performing the test, the general and detail test
procedure, and the maximum allowable VSWR.
a.
Using the VSWR traces of 4.6.2.1.1.4, the VSWR shall be tabulated at the frequency increments specified
in 4.6.2.1.1.4.
b.
Prior to accomplishing the VSWR measurement, adjustments should be made to insure that the frequency
and sweep width of the sweep signal generator are set to the desired bandwidth within the limitation of the
equipment. (Additional sweep generators shall be used if required to achieve the desired bandwidth.)
Precaution shall be taken to insure that the X-sensitivity of the recorder is adjusted to accommodate the
entire sweep and that the plot will be approximately in the center of the graph paper for the entire frequency
range.
4.6.2.1.1.5 Accept-reject criteria (procedure I). If the VSWR of the equipment under test exceeds the value
specified in the applicable detail specification, the equipment shall be considered to have failed the VSWR
engineering acceptance test.
4.6.2.1.2 Procedure II (VSWR comparison test). The VSWR comparison test shall check the electrical
performance of the equipment before, and after, certain mechanical and environmental tests.
4.6.2.1.2.1 Test conditions. Test conditions for procedure II shall be those applicable to the method selected
4.6.2.1.2.2 Test method I: Slotted line. When using the slotted line method, measurements shall be made at
frequency increments not greater than 0.02 GHz between 0.03 and 0.50 GHz, 0.05 GHz between 0.50 and 5 GHz,
0.10 GHz between 5 and 10 GHz, and 0.20 GHz above 10 GHz. If values of VSWR are within the band of doubt, the
VSWR shall be measured in sufficiently close increments to define a smooth curve structure, but at increments not
greater than those specified in 4.6.2.1.1.2. The measured data shall be recorded on a tabulation sheet or plotted on
8- by 10-inch graph paper.
4.6.2.1.2.3 Test method 2: Reflectometer. The reflectometer method shall be accomplished as specified in
procedure I (see 4.6.2.1.1.3).
4.6.2.1.2.4 Test method 3: Swept slotted line. The swept slotted line method shall be accomplished as specified
in procedure I (see 4.6.2.1.1.4).
4.6.2.1.2.5 Accept-reject criteria (procedure II). If the reflection coefficient of the equipment as measured prior to,
and after, mechanical or environmental tests, fails to remain within ± 10 percent within the neighborhood of ± 2
percent frequency search, or 0.02, whichever is greater; or if the VSWR exceeds the value specified in the detail
specification, the equipment shall be considered to have failed the VSWR comparison test.
4.6.2.1.3 Procedure III (VSWR production test). The VSWR production test shall determine the VSWR of the
production equipment.
4.6.2.1.3.1 Test conditions. Test conditions for procedure III shall be those applicable to the method selected
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