How to Test a Coax Cable Signal with a Multimeter

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Did you know that coax cables are one of the top materials used for networking an office or home? Whether it’s for cable, internet, or satellite, coax cable has a potential application in many rooms of a business or home.

This cable is utilized in businesses and homes as part of video and audio equipment, as it allows effective transmission of data. Also known as coaxial cable, these cables are an integral part of computer and telephone networks and also cable TV systems.

If not used properly, there are bound to be many problems in the video or audio reception. Actually, there’s no point in purchasing costly and high-tech TV or computer sets if the cabling is not done properly. You must check the cable as soon as you encounter a reduction in internet speed or bad picture quality. 

What is a coaxial cable? 

In case you didn’t know, a coaxial cable is utilized for transmitting high-frequency signals for communication such as satellite signals or video. Electrical interconnect isn’t glamorous, but it’s an essential detail that’s often ignored.

Have you ever heard somebody say, “worked much better in the store?” You will find many reasons for that.

Remember that a coax cable has two conductors that share a single common axis. A coax cable features a solid copper or copper plated conductor surrounded by dielectric insulating material. That dielectric is then surrounded by a braid or foil shielding that forms the outer conductor.

That outer conductor also protects against electromagnetic interference from external noise sources. A few coaxial cables are determined with an RG designation. Remember that RG refers to Radio Government. The number following is the specification identification, and the number value is arbitrary. 

It’s worth mentioning as well that high quality coaxial cable is utilized for the following:

  • TV antenna
  • Satellite master antenna television 
  • High-definition TV
  • Satellite TV
  • Cable TV
  • Broadband
  • Very small aperture terminal, satellite communications such as broadband 

Three of the most typical types of coax cables utilized for such applications are RG11 (high grade), RG6 (medium grade), and RG59 (low grade). Coax cable for such applications provides an impedance of seventy-five ohms. 

RG59 cables utilize a twenty or twenty-two AWG center conductor. On the other hand, RG6 cables feature an eighteen AWG center conductor. Ultimately, RG11 cables utilize a fourteen AWG center conductor. Please take note the smaller the AWG number, the bigger the diameter of the center conductor. 

You will find much variance in the cable specification in every class. An economy RG6 might have a small aluminum braid and a copper-plated steel center conductor rather than a high-performance RG6 cable, along with a sophisticated dielectric and quad-shield shielding. 

Coax signals for HDTV and videos

Many analog video cables are coax cables. For instance, an S video cable is two mini-coax seventy-five-ohm cables mixed in a common outer jacket. S video keeps the chrominance and luminance signals divided. One line brings the luminance signals, the other brings the chrominance signals, while the other two lines are ground wires.

On the other hand, component video cables utilize three separate seventy-five-ohm coax cables along with connectors at every end. The three cables are within a single jacket or three separate cables. That enables individual transmissions for the red signals, green signals, and blue signals. 

Serial digital interface (SDI) is considered the standard for digital video transmission over coax cable. Moreover, THE SMPTE 295M standard offers a maximum distance of three hundred meters for standard-definition television and 140 meters for HDTV.

You see, SDI offers a method for sending uncompressed digital audio, video, and other data between video services. 

Signal loss in coax cables 

One of the key factors when picking a cable is a calculation of signal loss, also known as attenuation. It’s often described as in decibels per distance. That ratio is also described as the log ratio of input or output. Keep in mind that a high-performance RG6 cable at 100 megahertz could have a signal loss of 6.4 decibels per hundred meters.

The decibel scale is logarithmic. Hence the signal in the cable will be lowered in signal strength by at least seventy-five percent over a distance of 100 meters. 

When the run is short, that might be a small consideration. Frequently, a signal loss will be of utmost importance, though. RG11 cable will normally show a signal loss of at least 4.5 decibels per hundred meters at 100 megahertz or a loss of at least eighty-two percent. 

Signal “leakage” takes place when the coaxial cable enables some of the signal to be radiated. Every coaxial cable has a specific amount of resistance and dielectric loss. Resistance loss is the biggest contributor to signal loss in coax cable. Losses caused by the resistance of the inner conductor differ with the conductor’s diameter. 

Can you test the signal of your coax cable with a multimeter?

Take note that you can’t test the signal’s strength by using a multimeter. Nonetheless, you can test for continuity by putting the multimeter in either diode or low ohms setting and attach one probe on the inner conductor at one end. 

Make sure you also attach the other probe on the other end inner conductor. You should receive continuity, and it may show zero up to two ohms, depending on the cable length. 

Repeat the entire steps with the outer screened conductor. As this is composed of a close-fitting screen mesh of fine wires, it must be zero. 

Is it linked to an antenna? You can attach it to the corresponding receiver, which ensures the outer conductor is linked to the ground of the receiver and checks for the reception of known signals. 

Take note that coax cables are created to have various impedance for various applications. There are fifty ohms for RF and seventy-five ohms for CCTV applications. 

Final Thoughts

High-performance communications need advanced interconnect technology. As our world continues to change, the system may need to support video, data, voice, and HDTV. The increasing size of networks, as well as the launch of high-speed access, produce a crucial necessity for high-performance and dependable cabling systems.

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