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Design >> RF Design >> peak power calculation
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Message started by watson822 on Dec 19^th, 2011, 4:57am

Title: peak power calculation
Post by watson822 on Dec 19^th, 2011, 4:57am

please help me calculate peak power in 802.11g 6Mbps 26dBm output, thanks

Title: Re: peak power calculation
Post by watson822 on Dec 20^th, 2011, 10:27pm

sorry, is peak voltage, not peak power, anybody know how to calculate? please kindly help~~

Title: Re: peak power calculation
Post by loose-electron on Dec 21^st, 2011, 10:17am

have you read the specification for the standard?

Title: Re: peak power calculation
Post by aaron_do on Dec 21^st, 2011, 4:57pm

First of all, peak voltage depends on the impedance level. Usually there is some VSWR specification for the standard. For instance, the transceiver may need to work for a VSWR of 5:1, and not explode with a VSWR of 10:1. So for a 50-ohm system with a VSWR of 10:1, you are potentially looking at 500 ohms.

Power = V²/R

You should also take into account the peak-average power ratio. It depends on the modulation scheme. For a sine wave it is 3 dB. But I'm guessing that for 802.11g it's higher.

Lastly, the peak voltage that you are actually going to get in your circuit can be highly dependent on the implementation. It depends on things like the harmonic content of the signal, and also whether or not there are any transmission lines between the components.

Hope I haven't missed anything out, and feel free to correct me anywhere...

cheers,
Aaron

Title: Re: peak power calculation
Post by weber8722 on Jan 2^nd, 2012, 1:44am

All looks right. Here is a nice detailed article :):

http://www.elliottlabs.com/documents/OFDM.pdf

For peak-voltage calculation you also have to be aware of peak-to-average power ratio. For a pure sine wave the peak power averaged over one RF period is constant, but modern modulation schemes such as OFDM have some amplitude modulation.

Bye Stephan

Title: Re: peak power calculation
Post by loose-electron on Jan 2^nd, 2012, 12:46pm

Sometimes ytou will find peak vs. average is a function of the modulation.
So its usually a good idea to check the specification.