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I bought a replacement wireless device. I want to compare it's stats with the old one.

I'm not very familiar with measuring units. Old device showed 60dbm (I think negative value) as signal strength. New device shows 25db. Can I somehow compare them? Perhaps using noise metric of the old device? IIRC noise was 92 or 97. My gut feeling tells me there should be a way because db I imagine should be signal/noise ration so I should be able to compare the two devices.

Anybody more knowledgeable?

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  • Google is. The third link down for me seems pretty useful. In summary: dBm is used as an absolute unit (in reference to 1mW) while dB is relational between two power values. Hopefully someone who knows hardware more can enlighten you as to which power values apply..
    – nerdwaller
    Sep 11, 2013 at 14:12
  • @akostadinov - You can't compare the two values ( two entirely differents of measurements ) unless you have additional information.
    – Ramhound
    Sep 11, 2013 at 14:23
  • I've looked at google already. I am thinking that knowing signal dbm and noise dbm I can compare with db. I'm not sure though and I'm not sure what the equation would be. So I hope somebody can tell here for sure.
    – akostadinov
    Sep 11, 2013 at 17:46

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dB is a relative unit that represents a ratio.
dBm is an absolute unit that is referenced to 1mW
1watt = 1000mW = 10log10(1000) = 30dBm (not 30dB)
So you can't convert dB to dBm.

More about converting decibels here: http://www.rapidtables.com/electric/dBm.htm

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  • You can compare a relative unit with absolute units if you know what absolute units produce the relation and the exact equation. Do you know that absolute units produce the relative db stat I see and what is the exact way to calculate. In this way I can produce the db value for the device diving absolute units and compare with the other one.
    – akostadinov
    Sep 11, 2013 at 17:48
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I think I got it. If we consider that the db value is a signal/noice ratio and we have to compare that with signal and noise expressed in dbm then we can calculate:

SIGNALdbm/NOISEdbm=Xdb

Since dbm is some kind of logarithm and we have a common base, then we just need to subtract the absolute values. In this case I think this is what needs to be done:

SIGNAL-NOISE=Xdb

In my case I compare (92 - 60) with 25 so it seems my old device had 32db and the new one only 25.

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