On 2006/06/13 17:59, Walter Haidinger wrote: > > I think CR31 just maps over the whole range of the card, > > so for a card with a more powerful amp, a particular CR31 setting > > relates to higher power output than it would on an ordinary card. > > Yes, that is what I figured too from the source. I have a 200mW card > here which I'd like to limit to 100mW (european limit) by setting the > appropriate txpower after accounting for antenna gain/cable loss. > > However, I doubt that e.g. subtracting 3dBm is sufficient, say > "ifconfig wi0 txpower 17" won't give me the desired 100mW because > the mapping is unlikely that linear or is it? > > The correct mapping is probably known only to the card manufacturer/ > firmware vendor (for the curious: Senao NL-2511CD PLUS EXT2).
More than that, it's differs from card to card (and channel to channel). Manufacturers perform calibration before shipping the card, and preset the levels for each channel, I remember looking at a couple of WAP11 (with similar serial numbers and presumably from the same batch) and seeing quite different figures on each of them. > While I'm at it an OT(?) question: > Does somebody know how to _simply_ (using a multimeter or an old > 20MHz scope) measure the power output of a wireless NIC? Just a rough > (+-10mW) estimate would suffice. The antennae are external so I have > access to the SMA. Then I could measure the mapping myself. Does anybody know if there are any cards with reasonably accurate signal strength indication? I've seen quite different figures for similar cards in similar situations so not sure if they're really believable... > Thanks for the reference. I'm trying to lower txpower to a _certain_ > level, though. Google will find ways to increase power but I'm > interested in the actual txpower value. So I wondered if ifconfig > displays txpower correctly. As it turned out, not for cards != 100mW. I think, even for 100mW prism cards, the display we have is only an approximation. I'm not sure there is a way to go from the unit-less figures to actual dBm with any degree of accuracy. Presumably this also changes according to temperature, age of the card, etc.
