ANy Mathmaticians out there?

[JohnWPB]

Ok, this is a strange one, I am working on a signal strength meter for one of my touch screens for the WiFi signal strength.

From what I can find 100db is 0% signal strength and 30db is 100% signal strength.

I want to somehow make a formula to spit out the signal strength on a scale of 1 to 100. I can't seem to wrap my brain around the equation!

For example using the above
100dB = 0%
30dB = 100%

then 65 =50% (I got this by just averaging the 2 numbers)

I just need an equation to be able to feed the dB to and get the percentage.

Any help is appreciated!

 

[IVB]

I didn't think it was linear, which, if true, would explain the confusion.

 

[BraveSirRobbin]

John:

It's been a while, but this isn't a linear relationship it is logarithmic so you can't take raw ratios between those two readings.

The equation is db = 20 log (Power).

I'm not exactly sure what your meter is measuring (attenuation loss I'm guessing) but HERE is some more info...

 

[WayneW]

And aren't those negative DB numbers? Otherwise something seems backwards.

 

[JohnWPB]

Yes, the numbers are negative.

I got the DB from a script that I wrote that returns the dB for the WiFi signal strength reported by the wireless adapter (Same thing windows uses to get the Very Low, Low, Good, Excellent from). When I had a "Very Low" reading the dB was ~-30. When I had an Excellent connection (Laptop right next to the wireless router) the dB was at -100.

It may not be perfect, but it will give a very close and accurate reading. I would rather see 80% Signal strength than to see 89db

I just need a way to have a small bit of VBScript to give me 0% for -30dB and 100% for -100dB.

 

[BraveSirRobbin]

Not promising anything, but can you give me the dB numbers for 25%, 50%, and 75% signals if it's not that big of a deal to do (%numbers are approximate, just wanted a span of readings)?

 

[DeLicious]

yes, if you can give a few more data points, it shouldn't be hard to do a regression on the values and come up with an approximate relationship for you.

 

[huggy59]

Found via Google:

The difference in decibels between the two is defined to be

10 log (P2/P1) dB where the log is to base 10.

If the second produces twice as much power than the first, the difference in dB is
10 log (P2/P1) = 10 log 2 = 3 dB.

If the second had 10 times the power of the first, the difference in dB would be
10 log (P2/P1)= 10 log 10 = 10 dB.

If the second had a million times the power of the first, the difference in dB would be
10 log (P2/P1) = 10 log 1000000 = 60 dB.

 

[JohnWPB]

Wow, I didnt think it was going to be this hard

More data points?

-100dB = 0%
-82 = 25%
-65 = 50%
-47 =75%
-30dB = 100%

I did this manually by taking the full strength and no strength DB and dividing by 2 (averaging them) to get the half way point, and then getting the half way points for 25% and 75% ect....

 

[mustangcoupe]

John,

I woke up this morning thinking about your question.................

invlog(signal in dbuV/20) or in excel =10^((signal level in dBm+107)/20) will convert the number from dBuV (logrithmic) to uV (Linear) BUT I am guessing you are looking at the the wrong numbers as the number should get closer to 0 or more positive for more signal.... Can you post the table of values for exactly what you are looking at.......As I am confused....


edited to correct formula

 

[mustangcoupe]

Are you maybe looking at the SNR colum (signal to noise ratio)

 

[DeLicious]

Wow, I didnt think it was going to be this hard

More data points?

-100dB = 0%
-82 = 25%
-65 = 50%
-47 =75%
-30dB = 100%

I did this manually by taking the full strength and no strength DB and dividing by 2 (averaging them) to get the half way point, and then getting the half way points for 25% and 75% ect....

these aren't data points... this is just implying a linear relationship from two data points.

 

[ccrrar]

Well for what it is worth when you are talking about dB with audible sound every 10dB is double the sound level. For example

if 10dB = loud then 20dB = 2 times loud, 30dB = 4 times loud, etc.....

Rob

 

[mustangcoupe]

Well for what it is worth when you are talking about dB with audible sound every 10dB is double the sound level. For example

if 10dB = loud then 20dB = 2 times loud, 30dB = 4 times loud, etc.....

Rob

In a RF world 3dB is twice the power

 

[huggy59]

I have to agree, it looks backwards for power level. Perhaps it is signal to noise ratio?

Mustang is correct... 3dB is a two-fold increase in power.


The Definition of Decibel
Decibel is a logarithmic unit used to describe the ratio of the signal level - power, sound pressure, voltage or intensity or several other things.

The decibel can be expressed as:

[1] decibel = 10 log( P / Pref )

where

P = signal power (W)

Pref = reference power (W)

A decibel is one-tenth of a Bel, a seldom-used unit named for Alexander Graham Bell, inventor of the telephone.

Note! Doubling the signal level increases the decibel with 3 dB ( 10 log (2) ).

If we know the decibel value and the reference level, the absolute level can be calculated by transforming [1] to:

P = Pref 10^(decibel / 10)


More at http://www.engineeringtoolbox.com/decibel-d_341.html