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 10Watts 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.

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

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    • Yeah good point and clever by Apple! If there are ieendd some early supply constraints, allowing all pre-orders on the same day might convince some buyers at the margin to go 3G and wait a little longer for delivery. That shifts the demand off the first shipments of wifi-only models

    • So I am subscribed to like 30 iPhone and iPad RSS feeds, yet oesohmw your post and email notice was the first to break the news. Nice work April 3rd is an odd release say as it is a Saturday. Do you think they want people to pre-order for in-store pickup to generate some retail hysteria? I would assume that no one that pre-orders will get it delivered on the 2nd.

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    • Thanks I should’ve cited my scruoe but instead I’ll bask in the glow a while longer!I vaguely recall that the iPhone 3GS date was a saturday as well. Not sure of the thinking overall but presumably it worked well enough then that Apple chose to do it again for the iPad (though I was hoping for April 1 imagine the humor!)If I had to guess I’d agree people generally don’t work on Saturdays so the stores are that much more likely to be packed. And offering in-store reservations is a fun way to add to that, provide a communal experience, but guarantee people that they will actually have one waiting for them.Re: early deliveries, again iirc Apple is pretty careful about working with its shippers to ensure no early (or late) deliveries. Amazon does this too with popular new books that are in super heavy pre-order demand (the Twilight, Harry Potters of the world).

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