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Frequency ranges used are within the range of 0.01 Hz to 0.1 Hz, where frequency selection depends on the load presented by the cable. Test voltage levels are either calculated using a multiple of the cable's nominal phase-phase voltage or via tables in IEEE 400.2; typically they are in the range of 1.5 U0 to 3 U0.
Assuming the dielectric properties of the material inside the cable do not vary appreciably over the operating range of the cable, the characteristic impedance is frequency independent above about five times the shield cutoff frequency. For typical coaxial cables, the shield cutoff frequency is 600 Hz (for RG-6A) to 2,000 Hz (for RG-58C). [10]
It is only after this round-trip delay that the short can be detected by the TDR. With knowledge of the signal propagation speed in the particular cable-under-test, the distance to the short can be measured. A similar effect occurs if the far end of the cable is an open circuit (terminated into an infinite impedance).
A time-domain reflectometer; an instrument used to locate the position of faults on lines from the time taken for a reflected wave to return from the discontinuity.. A signal travelling along an electrical transmission line will be partly, or wholly, reflected back in the opposite direction when the travelling signal encounters a discontinuity in the characteristic impedance of the line, or if ...
In telecommunications, return loss is a measure in relative terms of the power of the signal reflected by a discontinuity in a transmission line or optical fiber. This discontinuity can be caused by a mismatch between the termination or load connected to the line and the characteristic impedance of the line.
The characteristic impedance of coaxial cables (coax) is commonly chosen to be 50 Ω for RF and microwave applications. Coax for video applications is usually 75 Ω for its lower loss. See also: Nominal impedance § 50 Ω and 75 Ω
A terminating resistor for a television coaxial cable is often in the form of a cap, threaded to screw onto an F connector. Antenna cables are sometimes used for internet connections; however, RG-6 should not be used for 10BASE2 (which should use RG-58) as the impedance mismatch can cause phasing problems with the baseband signal.
The conventionally used aid in cable fault testing and location is the cable test van. The van is installed with conventional cable measuring systems for quickly reaching the location of any cable fault. In 20 years that followed, over 2000 fault location vehicles were manufactured, more than half of which were intended for the former USSR.
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