P72

Effective Radiated Power Basics

Establishing any station is a game of gains and losses.  When a transmitting station is heard at a distant location, how well the station is heard will be the aggregate of all radio energy leaving the transmitter antenna.  This includes transmitter power, connector losses, coax cable losses, antenna matching and the antenna gain.  This total combined output is termed the Effective Radiated Power (ERP).

Note that antenna gain is measured in decibels.  If 10 watts is transmitted into an antenna with a gain of 3dB (doubling) then, ignoring cable losses, the ERP would be 20 watts.

This can be a safety consideration when transmitting higher power levels into very high gain directional antennas.  The amount of RF power leaving the transmitter may be deemed to be a safe level, but in the direction the antenna is pointing, the ERP power level may reach dangerous levels at close range.    This risk is mitigated if the antenna is mounted above a height of people movement.

In this example we see a HF beam antenna on top of a building, but close to an adjacent residential building of greater height.  If the ERP was sufficiently high, the transmitted energy could put adjacent residents at risk.  In this instance, the image was taken from a nearby hotel room.

Here is an on-line calculator where Effective Radiated Power can be calculated.

https://calc.commscope.com/qerp.aspx

The Foundation Level Study Guide

All Blue Tiles form part of the syllabus for the Foundation Level Recognition Certificate (operator licence).  A primary source of information for many of the blue tile topics can be found within the Foundation Level Study Guide.  This is a free download available at:

https://vkradioamateurs.org/flsg/  This is a digital book and contains many links to other resources and explanatory videos.

Information on RF exposure Safety can be found from Page 80 in this book

ACMA Syllabus Extract

According to the ACMA Foundation Syllabus, the required knowledge on this topic is:

5.10   Effective Radiated Power (ERP)

Recall that ERP is the product of transmitter power and antenna gain.

Recall that antenna gain is generally expressed in decibels.

9:16 Radio waves can be dangerous

Recall that electromagnetic radiation (EMR) can be dangerous and higher frequencies and power levels and proximity to the source increase the danger.

9.17 Safe Distances

Recall that a safe distance from an antenna depends on the ERP, operating frequency, antenna type and orientation.