The Mystery between RF Output Power and EVM (Error Vector Measurement) for WiFi Products

Taipei, Taiwan WiFi products are marked with High power promotion, are they real High Power?
All electronic products’ or devices’ output power are counted by Watt. There are three units seen in WiFi products frequently, dBm, dBi, and EIRP. Regarding dB and Watt conversion table you can link to http://www.asiarf.com/dB-to-Watt-Conversion-Table-support-view-5.html take a look.
Below more detail about these units:
As we know Watt is the electronic power unit.
dBm is an abbreviation for the power ratio in decibels (dB) of the measured power referenced to one milliwatt (mW). Most of vendors mark the highest output power is based on IEEE802.11b mode.
dBi is the forward gain of an antenna compared with the hypothetical isotropic antenna, which uniformly distributes energy in all directions.
EIRP (Equivalent isotropically radiated power) is the sum of output power of WiFi device and transmission loss (cable loss) and antenna’s gain. Normally you will see the amount of EIRP is big number like 20Watts or even more. Donot be scared, go to check and see, you will find out where you need to watch out for the radiation.
There is another important index called EVM (Error Vector Measurement). The lower percentage, the quality of signal transmission is better. Like 3% is better than 5%. If the EVM is higher than 5.5%, then you can see the signal index is good, but transfer the data, no. That means you cannot get homepage from internet either. Most of vendors’ QC index is 5% or 5.5%, some special high quality products is 3%, meanwhile the output power index will be a little lower. For the linking quality is also much better. From now on, if you compare the high power products, you should look at both indexes.
Hope these is helpful for your choice with High Power Products.