MIL-STD-220C
4.1.2.3 Sources and types of errors.
a. Systemic errors Systemic errors are caused by imperfections in the test equipment and test setup. If these errors do not vary over time, they can be characterized through calibration and mathematically removed during the measurement process.
b. Random errors. Random errors vary as a function of time. Since they are not predictable, they cannot be removed by calibration.
c. Drift errors Drift errors occur when a test systems performance changes after a calibration has been performed. They are primarily caused by temperature variation and can be removed by additional calibration. By constructing a test environment with stable ambient temperature, drift errors can usually be minimized.
These situations are listed for reference only, it is expected that the test agency will select appropriate equipment that is capable of performing the test and has the stability to have a reading repeatability of ± 1dB made on the same filter at the same time, temperature and frequency conditions as the first reading.
4.2.2 Coaxial lines, connectors, and switches. All coaxial lines shall be RG-214/U, or equivalent double shielded cable, and shall conform to MIL-DTL-17. It is essential that cable with the characteristic impedance of type RG-214/U be used to connect the isolation attenuators together for the filter 'out' condition and to connect the component to the isolation attenuators for the filter 'in' condition. The length of cable connecting the isolation attenuators for the filter 'out' condition shall be within ±6 inches (±152.4 mm) of the combined length of the two cables connecting the component to the isolation attenuators for the filter 'in' condition. Type N, SMA or equivalent RF 50 ohm coaxial connectors conforming to
MIL-PRF-39012 shall be used where applicable. When coaxial switches are used, they shall have a 50 ohm characteristic impedance, and a maximum voltage standing wave ratio (VSWR) of 1.1 to 1 at the frequency of measurement.
4.2.3 Isolation attenuators. Isolation attenuators are not necessary when testing is conducted using a network/system analyzer that has a 50 ohm input and output ports.
4.2.4 Insertion loss measurement. When the component under test has no provisions for coaxial connections, the insertion loss measurements shall be recorded after the component's input and output terminals are surrounded by RF shielding that has a common electrical connection with the shielding of
the test equipment or test equipment cables. Use adequate clamping means on the isolation fixture when using a network/spectrum analyzer (see figure 2 and figure 3).
4.2.5 Standard attenuator. A standard attenuator for testing with network/spectrum analyzer shall be provided with the following characteristics:
a. Attenuation of 50 ± 0.5 dB over the frequency range of 150 kHz to 1,000 MHz, inclusive.
b. Maximum VSWR of 1.2 to 1 over the frequency range of 150 kHz to 1,000 MHz, inclusive. c. Input and output impedance of 50 ohms.
The standard attenuator shall be inserted into the system in place of a component, to test for proper operation as specified (see 4.1).
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