MIL-DTL-28830E
4.7.10 Impedance (see 3.5.9).
4.7.10.1 Specimen. The specimen shall be 10 feet (3.05 meters) minimum or 2 dB maximum at 3
GHz whichever is shorter.
4.7.10.2 Procedure. The specimen shall be prepared for testing by assembling appropriate
connections to the cable ends. The equipment shall include a time domain reflectometer (TDR). The
rise time of the TDR shall be 150 picoseconds or less, and the vertical sensitivity of the system shall
provide for a minimum resolution of 0.5 ohm per centimeter (cm). A precision 30-cm air line of the
same nominal characteristic impedance as the specimen shall be connected between the TDR and
the connector-cable assembly. The characteristic impedance of the specimen shall then be
measured compared to the precision air-line. The connector-cable assembly shall then be turned
end-to-end and the measurement repeated. For cables of other than 50 and 75 ohms characteristic
impedance, where precision air-lines, loads, or proper impedance measuring equipment are not
available, the characteristic impedance may be determined by calculation from the capacitance
measurement determined (see 4.7.9 ) and the velocity of propagation measurement determined (see
4.7.8), using the following formula:
101,670
Zo =
Velocity of propagation (%) * Capacitance (pf/ft)
4.7.11 VSWR (see 3.5.10). The VSWR of 500 foot (152 meters) minimum length of cable shall be
measured over a frequency range as specified (see 3.1). A swept frequency technique capable of
measuring a VSWR of 1.06 or less shall be used. The measuring system may be in the form of
directional couplers, a hybrid, or a slotted line and shall have a directivity of at least 30 dB at the
highest frequency of measurement.
4.7.12 Cold bend (jacketed cable only) (see 3.5.11). A straight section of finished cable, whose
length shall be sufficient to make one revolution around a mandrel with a diameter as specified (see
3.1), in the case of 1.625 inch diameter cable, it shall be one-half revolution, shall be placed in a
chamber and subjected to a temperature of -30ºC ± 2ºC for at least 48 hours. After this period, the
cable shall be removed and within 30 seconds subjected to a 180º bend around the mandrel
specified.
4.7.13 Flexibility (see 3.5.12). The length of cable to be flexed shall be sufficient to provide three
complete coils around the mandrel with a diameter as specified (see 3.1). One end of the cable shall
be clamped circumferentially to the mandrel at any two points, approximately 45º apart. The
specimen shall then be coiled around the mandrel for not less than one complete revolution and
then uncoiled and straightened by pulling on the free cable end a total of 20 times. (The mandrel
shall be rotated not less than 20 times, 720°, to accomplish this.) Coiling and uncoiling shall be
performed at a rate of not less than one revolution per minute (rpm) nor more than 5 rpm; that portion
of the cable which is coiled about the mandrel shall be kept snug about the mandrel at all times (by
maintaining tension in the cable). Although no special tools shall be used during the bending of the
cable, a mechanism may be provided to guide the cable on the mandrel. After the twentieth cycle,
while coiled.
14
For Parts Inquires call Parts Hangar, Inc (727) 493-0744
© Copyright 2015 Integrated Publishing, Inc.
A Service Disabled Veteran Owned Small Business