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EIRP and ERP

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These two acronyms relate to a scale of measurement for RF transmission. They’re important in the field of UHF RFID as the two scales are used in different regions of the world to measure the power transmitted by the reader. Specifically, those systems that operate under the FCC regulations are limited to 4W EIRP effective radiated power, and those within the ETSI region are limited to 2W ERP.

So, what does this mean? The table below shows a comparison of the two methods of measurement:

  What does it stand for?Region UsedMax Radiated PowerAntenna Gain Measurement
ERP Effective Radiated Power ETSI 33 dBm or 2W dBd
EIRP Effective Isotropic Radiated Power FCC 36 dBm or 4W dBi

 

It is beyond the scope of this post to discuss the theory behind the differences; however, it is possible to convert EIRP based measurements to ERP; a simple equation governs this conversion:

  •  dBm (ERP) = dBm - 2.15 (EIRP)

So, for example, the maximum radiated powers in the ETSI and FCC regions can be seen below:

  • FCC: 36 dBm EIRP - 2.15 = 33.75 dBm ERP
  • ETSI: 33 dBm ERP + 2.15 = 35.15 dBm EIRP

These conversions are also important when selecting antennas and determining legal transmit powers. The gain of an antenna is often measured in dBi regardless of where it is intended to be used. In order to ensure the maximum transmit power is within regulations it’s important to ensure the system is set up using like for like measurements (i.e. dBd = dBi - 2.15).


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Impinj (NASDAQ: PI) wirelessly connects billions of everyday items such as apparel, medical supplies, and automobile parts to consumer and business applications such as inventory management, patient safety, and asset tracking. The Impinj platform uses RAIN RFID, delivering information about items to the digital world and enabling the Internet of Things.