Re: [NTLK] Power Consumtion of WaveLAN card

From: Humphreys, David (
Date: Fri Mar 15 2002 - 14:37:48 EST

> -----Original Message-----
> From: Jim Witte []
> Sent: Friday, March 15, 2002 01:24p
> To:
> Subject: Re: [NTLK] Power Consumtion of WaveLAN card
> Can anyone here (PCBMan?) shed light on whether there is a
> theoretical
> minimum power requirement for wireless cards?

First let me thank you Jim for thinking I could be of some help here.

As it happens, I don't have any wireless cards of my own but I can give
you some generalized RF theory to chew on.

And before the RF gurus amongst us rip this up, remember I said 'generalized'.

When the RF leaves the antenna, it starts to spread out. As the distance
between the TX and RX increases the power has to spread over a larger and
larger area. If you have to put 1W of power into the antenna to give a
particular level of signal at 1 meter, you would need to put 4W in to get
the same level 2 meters away. You would need 9W at 3 meters, 16W at 4 meters etc.

Obviously, the o/p power is a fixed value for a wireless card so the received
power will be proportional to the square root of the distance.

What does this all mean? Well the minimum power requirement for a particular
card will be dependent on:

The distance between stations.
The method of RF generation.
The power out of the antenna.
The efficiency of the card.
The weather ;)
and a number of others...

A particular power out will require a particular power in. It is hard to
put a one-size-fits-all figure on it. I would generally say that an increase
of 10-15x the quiescent current of the card for the duration of the transmission
would be about right. Some may be more, some less. Its just a ball-park figure.



Theory is when you know everything and nothing works;

Practice is when everything works and nobody knows why.

Here we combine theory and practice:

Nothing works and nobody knows why.

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