Re: prism2 silence value question

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On Tue, 28 Jan 2003, M. Warner Losh wrote:

> : Any thoughts from the peanut gallery?
>
> My guess is that there's an external amplifier on the 200mW card and
> there isn't on the netgear card.  This "distorts" the power levels and
> thus the measurement of the signal/silence levels.
>
That was my initial thought as well. Unfortunately, it's tough to get the
same frame to come out of pcap on both interfaces to do direct comparison
of the values to correlate between the two cards...

> : Alternately, any suggestions on a good way to normalize the data I'm
> : getting so that either card would be useful?
>
> Good luck.  I've tried to come up with a good formula for this that
> works for my 10 cards and have failed.
>
I've been toying around with the idea of calculating some sort of running
standard deviation values, but that's really only useful for following a
signal delta (which is admittedly useful for some applications).

If you're game, I'd love to try and gather some data from as many prism2
cards as I can and see if I can hack something together to help regulate
this. There have to be some assumptions we can draw to help this out. For
example, does the following seem reasonable in your experiences?

 - follow signal values and track a min and max seen value
 - if max < 27, don't correct
 - if min > 27, correct by subtracting 27 (the magical floor)

I have as yet to see a situation where I have values popping up on both
sides of 27 from a card, it seems to either be a floor or a max value for
silence. Then again, I've only got 4 cards available to me (dlink DWL-650,
compaq card that looks liek a dwl-650, Netgear MA401, and the Demarc
200mw)


- -d

"You see, wire telegraph is a kind of a very, very long cat.
 You pull his tail in New York and his head is meowing in
 Los Angeles. Do you understand this? And radio operates
 exactly the same way: you send signals here, they receive
 them there. The only difference is that there is no cat. "

                                           --Albert Einstein

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