MIL-PRF-31031B
4.6.24 RF transmission loss (see 3.27). RF transmission loss shall be determined in accordance with
the following procedure or an alternate method acceptable to the Government. In the event of dispute, the
method outlined herein shall be used.
4.6.24.1 Test sample. The test sample shall be a short cable assembly with the connector under test
on one end and the mating type connector on the opposite end of the applicable cable (see 3.1). The test
sample cable shall be a section of the long cable measured in step 3 of 4.6.24.2.2. The length of the test
sample should be such as to minimize the loss due to the cable alone and sufficiently long so that there is
at least a short length of cable whose characteristics remain unchanged by the cable stripping and
connector assembly procedure. The cable length in the test sample is defined as the distance from face
to face of the cable dielectric after stripping the cable for the connectors.
4.6.24.2 Procedure. The basic measuring system shall be arranged as shown on figure 5. The test
frequency range shall be from 2 GHz to the specified upper limit (see 3.1).
4.6.24.2.1 System check.
a. RF bridge directivity shall be checked in accordance with the standing wave ratio/return loss
procedure as specified in 4.6.11.
b. Verify the system amplitude accuracy by measuring the RF transmission loss of calibrated
attenuators over the specified swept frequency range (see 3.1). The calibrated attenuators shall
have nominal values covering the range of anticipated measurement loss values. Their calibration
data shall be accurate to the following limits.
Nominal value
Uncertainty
(dB)
(dB)
Up to 10
.1
Over 10 to 20
.2
Over 20 to 30
.3
Over 30 to 40
.4
Over 40 to 50
.5
System amplitude accuracy shall be 5 percent or better over the specified frequency range (see 3.1).
4.6.24.2.2 Measurement. Successive sweeps over the test frequency range are made with the test
system arranged as shown in steps I through 6 of figure 5. An X-Y recording displaying RF transmission
loss in dB as a function of frequency shall be made at each step.
The length of the applicable long cable measured in step 3 should be such as to have an RF transmission
loss of not less than 2 dB at 2 GHz. The physical length shall be measured and recorded. Attenuation of
the cable is assumed constant over the length and is calculated as follows:
Attenuation (dB/inch) = RF transmission loss (dB) ÷ Length in inches
Steps 1, 2, 3, and 6 are performed with input to the signal processor from detector 2 through the
transmission channel.
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