How to read RF Signal (WiFi) in dBm

Discussion in 'Wireless & RF Design' started by dante_clericuzzio, May 29, 2017.

Mar 28, 2016
172
3
My wifi signal is within the range around -25 to -35 dBm base on the meter reading is it good or bad?

What is the worst (lowest) and the best (maximum) of WiFi signal measured in dBm?

and why is it measured in negative value?

2. Papabravo Expert

Feb 24, 2006
11,210
2,214
It is actually pretty good.

dBm is a measurement with respect to a power level of 1 milliwatt or 0.001 watts. A positive dBm value would represent a power greater than one milliwatt, and a negative dBm value represents a power level smaller than 1 milliwatt.

$-25\;\text dBm \;=\;10\times\math log(\frac{P}{.001})$
$-2.5\;=\; \math log(\frac{P}{.001})$
$10^{-2.5}\;=\;\frac{P}{.001}$
$3.1623\;\times\;10^{-3}\;=\;\frac{P}{.001}$
$3.1623\;\times\;10^{-6}\;=\;\text P\;\approx\; 3.2 \mu \text watts$

$-35\;\text dBm \;=\;10\times\math log(\frac{P}{.001})$
$-3.5\;=\; \math log(\frac{P}{.001})$
$10^{-3.5}\;=\;\frac{P}{.001}$
$316.23\;\times\;10^{-6}\;=\;\frac{P}{.001}$
$316.23\;\times\;10^{-9}\;=\;\text P\;\approx\; .32 \mu \text watts$

Typical minimums for a modern receiver are -125 to -135 dBm so you are several orders of magnitude above the minimum receiver threshold.

Last edited: May 29, 2017
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3. crutschow Expert

Mar 14, 2008
16,840
4,586
dB is the logarithmic ratio of two powers (dB= 10*log(P1/P2).
For dBm a value of 1 mW is used for P2.
So a negative dB simply means that the P1 value you are measuring is less than 1 mW.
Thus -25dBm represents a power of ≈3.2μW.

Where are you measuring this -25 to -35dBm?
This value will vary depending upon how far you are from the WiFi modem.

dante_clericuzzio likes this.

Mar 28, 2016
172
3
the wifi modem just next to my phone

5. Dodgydave AAC Fanatic!

Jun 22, 2012
6,544
1,049
Any value over -60dbm to -80dbm is medium signal, anything between -40 to -60 is excellent, download Wifi analyser on Android by Farproc.

Lower is strongest.

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6. John Furystrom New Member

Jun 19, 2017
4
0
Highly recommend to try the WiFi analyzer . With the help of the application, you can quickly and efficiently find and eliminate the cause of a bad signal. An intuitive interface will save your time. First check your network to be sure that the source of the problem not in the hardware part, after you can try to reinstall your smartphone software or try to visit service center.