What You Need to Know VLF Cable Testing and Why it is Preferred

With the rise of new technologies such as wireless and fiber optic cables, communication is now more efficient. Modern communication systems have created the need for higher-frequency testing at lower voltages to detect broken or defective signal lines. Also you can prefer a clock oscillator that is an electronic circuit that generates a consistent and regular electrical signal, typically used to track time or synchronize the operations of various devices in computers and electronics.

VLF cable testing has become highly popular due to its versatility and ability to detect faults quickly and accurately without damaging the communications system. See how it was done here for a clearer picture of the whole process. It’s recommended to get in touch with experts in case you’re having issues with your cables.

VLF Cable testing is a way to identify problems in the cable itself and the connections. There are many different reasons why these types of faults could occur, but during VLF Cable Testing for a particular fault type, technicians will often try to determine if it’s a problem with the cable or one of its connections.

VLF Cable Testing Underlying Technology

The basic principle underlying this technology is to use low-frequency electromagnetic waves traveling down an open line to detect any weak signals superimposed on them. A cable tester typically consists of both a power amplifier and power supply and an audio generator, one or more signal generators (for example, a tone generator), and a frequency counter (to determine the frequency of the generated signals), and a peak detector.

For the testing of digital transmission systems, the “golden-ear” method is used, i.e., comparing two signals to detect any differences in their frequencies.

VHF cable testers are used to isolate faults in CATV circuits by measuring the return loss of the cable at several frequencies. The test normally consists of testing for faults, both on one end and on both ends of the cable.

 Types of VHF Cable Testing

There are two basic types of VHF cable testing: “near field” and “far-field.” The near field method is often used to measure the power level in a cable. A near-field instrument can measure small voltages (less than 1 V) at distances up to several meters, depending on the type of instrument.

A far-field tester measures voltages across a very large distance, several hundreds of meters or kilometers. A VHF tester must have an antenna connected to the cable at both the input and output so that the oscillator can transmit and receive signals across the entire length of the cable.  For this type, an instrument itself will contain a transmitter and/or receiver, an oscillator, a display, and possibly a means of controlling test voltages.

Near Field Method

The “near field” method is used to measure positive voltages at positions in the cable, as well as power levels for signal testing.

VHF cable testers are used to detect faults in coaxial cable, primarily for time-division multiplex (TDM) systems. They can also be used for the testing of microwave and high-frequency systems.

A VHF tester is essential to remove the noise from a TDM channel and identify the particular bitstream. VHF cable testers are used in conjunction with a spectrum analyzer, microstrip line analyzer, or other devices which can measure the amplitude of a signal at a number of different frequencies simultaneously. The most common method of testing is to use a sine wave modulated with data at 1.5 kHz (the carrier frequency) and compare it with a known bitstream that has been internally generated by the equipment.

Intermittent Faults Caused by Noise

In the digital world, cables are tested for intermittent faults caused by noise, such as inter-modulation distortion and coherent noise. The most common test signals are 1.5 kHz square-pulsed sinusoids, but many other modes can be used.

Coherent noise modulates at the same frequency and amplitude as the signal; inter-modulation distortion modulates at frequencies that are a harmonic of the signal’s frequency.

Intermodulation Distortion

Intermodulation distortion is caused by matching networks, T-connectors, RF amplifiers, mismatches in cable capacitance or inductance, or nonlinear loads such as wires running across many other cables. The most common test signals are 5 kHz sine with 1 kHz sine and 7 kHz sine with 3 kHz sine.

An independent source of test signals is necessary because there are differences in the response of each type of connector to a given signal. Intermodulation distortion can be eliminated using a slightly different signal, such as 2 kHz sine with 5 kHz sine. However, this can lead to other problems such as cable telemetry and data synchronization problems.