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G8MNY > TECH 14.03.04 12:49l 66 Lines 3292 Bytes #999 (0) @ WW
BID : 48241_GB7CIP
Read: DL7NDF DB0FHN GUEST OE7FMI
Subj: dBW & dB Levels made easy.
Path: DB0FHN<DB0RGB<OK0PPL<DB0RES<ON0AR<GB7CIP
Sent: 040314/0943Z @:GB7CIP.#32.GBR.EU #:48241 [Caterham] $:48241_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
(Updated Mar 04)
Deci Bells (1/10 Bell) which are on a logarithmic scale are used when large
ranges are used or many gain/loss terms have to be considerd. As these are logs
the dB can just be added rather than using gain factors or loss fractions that
have to be multiplied together.
dBW
The Formulae for POWER is 10log POut/1WATT, which gives this easy to remember
1dB step table based only on +/- 3, 6 & 10dB. Where Log = log base 10, not E or
Natural Logs.
Note, dBW has "0" referenced to 1 Watt.
And dBm has "0" referenced to 1 mW, so 30dBm = 0dBW
+3dB is doubling the power, -3dB is only a half.
+6dB is Quadrupling power, -6dB is only a quarter.
+10dB is 10 times the power, -10dB is only a tenth.
mW dBW Watts dBW Watts dBW Watts dBW Watts dBW
10 -20 0.1 -10 1 0 10 10 100 20
12.5 -19 0.125 -9 1.25 1 12.5 11 125 21
15.65 -18 0.1565 -8 1.565 2 15.65 12 156.5 22
20 -17 0.2 -7 2 3 20 13 200 23
25 -16 0.25 -6 2.5 4 25 14 250 24
31.25 -15 0.3125 -5 3.125 5 31.25 15 312.5 25
40 -14 0.4 -4 4 6 40 16 400 26
50 -13 0.5 -3 5 7 50 17 500 27
62.5 -13 0.625 -2 6.25 8 62.5 18 625 28
80 -11 0.8 -1 8 9 80 19 800 29
dB
For Voltage and Currents the formulae is 20log in/out, which gives this easy to
remember 2dB step table based only on +/- 6, 12 & 20dB. Where Log = log base 10
not E or Natural Logs.
+6dB is doubling the level, -6dB is only a half.
+12dB is Quadrupling level, -12dB is only a quarter.
+20dB is 10 times the level, -20dB is only a tenth.
Note +1dB is about +11% (111%), & -1dB is about -9% (91%) of the level.
Ratio dB Ratio dB Ratio dB Ratio dB Ratio dB
0.01 -40 0.1 -20 1 +0 10 +20 100 +40
0.0125 -38 0.125 -18 1.25 +2 12.5 +22 125 +42
0.01565 -36 0.1565 -16 1.565 +4 15.65 +24 156.5 +44
0.02 -34 0.2 -14 2 +6 20 +26 200 +46
0.025 -32 0.25 -12 2.5 +8 25 +28 250 +48
0.03125 -20 0.3125 -10 3.125 +10 31.25 +30 312.5 +50
0.04 -28 0.4 -8 4 +12 40 +32 400 +52
0.05 -26 0.5 -6 5 +14 50 +34 500 +54
0.0625 -24 0.625 -4 6.25 +16 62.5 +36 625 +56
0.08 -22 0.8 -2 8 +18 80 +38 800 +58
There are other dB standards in use not always measuring the same item!
eg..
dB SINAD is a ratio of signal in noise & distortion.
dBuV where the "0" = 1uV of signal. eg 12dB sinad @ -6 dBuV
dBc where the "0" = full carrier power. eg spurious = -60dBc.
/QSL
73 De John, G8MNY @ GB7CIP
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