How to Measure the DB Loss of Coax

Written by alexander rudinski
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How to Measure the DB Loss of Coax
Decibel loss can be measured with the length of the coaxial cable. (Coaxial cable image by lefebvre_jonathan from Fotolia.com)

As electrons travel through a medium, their voltage decays slowly. This is due to the resistance of the medium to electricity, more technically called impedance. As the distance the electrons must travel through the medium increases, the impedance has a cumulative effect. This means that the longer your coaxial cable, the more electricity you lose. This translates into a loss of decibels, abbreviated dB. Because this loss is predictable based on length, the dB loss can be calculated. However, the formulas for this calculation are incredibly complex, to the point where the average person could not understand or use them. As a result, it is simplest to use one of the calculators available online to calculate dB loss.

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Instructions

  1. 1

    Determine the type of coaxial cable you have as well as its resistance in ohms. This information should be listed on the packaging, but as a rule of thumb, television coaxial cable is rated at 75 ohms, while radio coaxial is rated at 50 ohms.

  2. 2

    Measure the coaxial cable. Do this by pulling the cable taut and laying it flat.

  3. 3

    Plug the length of your cable into one of the online calculators available. There is one listed in the Resource section of this article.

  4. 4

    Determine the significance of this loss to your specific application. While most loss is minimal unless you are using extremely long cables, this loss varies by frequency. This means that certain critical frequencies may be attenuated to an unacceptable degree, which will require you to connect a signal booster to the coaxial cable to compensate for the dB loss.

Tips and warnings

  • To avoid dB loss due to length, keep coaxial cables as short as possible.
  • All cables are affected by dB loss, so all cables in a project should be as short as they can be, though loss does not start to become a problem until about 50 feet.

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