How To Calculate RF Path Loss and Link Budget?

How To Calculate RF Path Loss and Link Budget?

17 January 2018 | Reading Time: 2 minutes

What Is RF Path Loss, And How Does It Affect The Link Budget?

In order to determine factors such as the required antenna gain levels, radio power levels and reciever sensitivity figures in a wireless system, system designers must first be able to devise the link budget.

But, in order to establish that link budget for a proposed path, it’s important to understand how to calculate RF path loss. This must account for all of the gains and losses from the transmitter, through the medium (free space, cable, waveguide, fiber, etc.) to the receiver in an RF path.

This post explores 8 key steps in calculating RF path loss in order to devise the link budget.

8 Steps To Calculating RF Path Loss And Link Budget

RF path loss includes the attenuation of the transmitted signal as it propagates, as well as the antenna gains, cable and connector losses. Where the losses may vary with time, such as ‘fading’, allowance is made within the link budget.

In order to devise a link budget, it is necessary to investigate all the areas where gains and losses may occur between the transmitter and the receiver. Although guidelines and suggestions can be made regarding the possible areas for losses and gains, each link should be analyzed on its own merit.

The following are recommended steps:

  1. Select a frequency – Certain system components are frequency sensitive such as cables, duplexers / couplers, free space path loss, or building material losses. Other components are not frequency sensitive, such as optical fiber, optical connectors and lasers.
  2. Determine the signal source’s output power – Will it be coupled directly from a base station or will it be coupled from a repeater?
  3. Specify the uplink and downlink system gain.
  4. Determine the passive losses in the path – Design for losses at the highest frequency. Include any splitters, coaxial cable and connectors.
  5. Select an Antenna – with the designed antenna gain.
  6. Compute the free space path loss.
  7. Add any additional losses that need to be accounted for – such as indoor walls and partitions or terrain, buildings and vegetation outdoors.
  8. Compute the Received Signal level expected. This is then be compared to the receiver sensitivity to establish a pass/fail criteria for the proposed link.

No real magic is required to make a reasonable prediction of the range of a given RF signal, it is a summation of all the above factors. Most of the parameters are easily gleaned from manufacturer’s data. That leaves only RF path loss and, in cases of heavy RF interference, RF noise floor as the two parameters that you must establish for your particular installation.


Gain the RF Knowledge You Need

As RF infrastructure forms just one aspect of wider passive infrastructure, it’s important to have an understanding of all components to ensure network success.

Our Passive Infrastructure Specialist courses cover every aspect you need to know; from RF Wireless Infrastructure Fundamentals, to Fiber Optic Infrastructure, to Structured Cabling Design and more. You can find out more with the full course listing here.

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