Regulating power in mW



  • Im wondering if there would be a option, to boost the atheros cards, because they go way over 200mW, but the most are set to factory default 28, 50, 70 ,…
    I'd need a option like the dd-wrt has for linksys wifi routers, where you can set the number of mW. Would this be possible to implement?

    Thanks,
    Sam



  • @ssam:

    Im wondering if there would be a option, to boost the atheros cards, because they go way over 200mW, but the most are set to factory default 28, 50, 70 ,…
    I'd need a option like the dd-wrt has for linksys wifi routers, where you can set the number of mW. Would this be possible to implement?
    Thanks,
    Sam

    Not that I am aware.  I am sure that this would violate some law in the USA with the FCC.



  • @sullrich:

    Not that I am aware.  I am sure that this would violate some law in the USA with the FCC.

    Actually it depends on the antenna db rating and the mw's, if you have a 2db attenna(factory) then 200mw would be ok, but a 20db directional +200mw is not legal.



  • The highpower atheros cards has different settings, if you set a highpower card (like the ubiquiti SR-5) to 10mw it actually sets the output power to something like 10mw +10dbi. This is done in the firmware of the card, so if you set it to 0mw on the driver the card will actually output 10dbi. Overdriveing a Atheros card will result in two things (both bad):

    1. Your card will be destroyed after some usage (depends on load etc.) as the overdrive will cause the radio chip to burn.
    2. While it will output maybe 2-3 dbi extra for a while it will also generate a lot of extra noise, so the gain will be pretty much eaten up by the added output noise.

    If you want more output power add a antenna instead, this will give you clean amplification.

    BTW. just fyi. Atheros cards has different amplifiers, so all atheros cards are not 200mw. They can be anything from 25mw to 400mw or more. Also, amplification drops when you increase the connection speed. So if your card can output 400mw at 1mbit it will most likely output about 95mw in 54mbit.



  • yeah, i know all that, but on some devices there is a mW ption, was just wondering if it would be possible here too:)

    Ive bosted several linksys wrt54g/s from the default 28mW up to 100mW and they are still working without problems (with broadcom chips…)

    Thanks for the answers!



  • We have the mW option, but we do not control the HAL, so we do not control the power output. If you set it to 99mW it will output as much as the card is rated for.



  • I have not measured it with an RF power meter, but it seems to me that the txpower attribute of the cisco a/b/g card is :

    2 txpower units ~ 1dB

    Had measured the cisco LMC 352 PCI card and found the reception index (0-100%) to be related with the RX input power, expressed in dBm, in the following  proportion :

    2% units ~ 1 dBm.

    Linearity from 10% to 90%, if I recall correctly, was within +/- 1,5 dB.

    So, if you need it displayed in mW you have to do the log -> linear conversion.

    What is easy to include in pfSense, is the RSSI to RX dBm conversion for the Atheros cards.

    It just takes a subtraction for it

    RSSI - 95 = RX input in dBm.

    Example : RSSI = 35 -> Rx = -60dBm

    Read it in a paper, but I can verify it also if you deside to include this option in a future release.


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