OpenBCM V1.08-5-g2f4a (Linux)

Packet Radio Mailbox

IZ3LSV

[San Dona' di P. JN]

 Login: GUEST





  
G8MNY  > TECHNI   07.09.23 10:20l 91 Lines 4263 Bytes #999 (0) @ WW
BID : 55319_GB7CIP
Read: GUEST
Subj: dBW & dB Levels made easy.
Path: IZ3LSV<DB0ERF<DB0RBS<DB0RES<ON0AR<IW0QNL<VE2PKT<OK2PEN<GB7CIP
Sent: 230907/0852Z @:GB7CIP.#32.GBR.EURO #:55319 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To  : TECH@WW

By G8MNY                               (Updated Jun 16)
Deci Bells "dB" & not "db" (Dolby audio system logo) are a 1/10 Mr Bell's unit,
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
  So 1uW = -30dBm or -60dBW

 +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   -12       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 & Currents the formulae is 20log out/in, 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.
(Level is Current or Voltage NOT POWER)
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!
e.g.
    dB SINAD is a ratio of signal in noise & distortion.
    dBm  used much for 600ê AF where 1mW = 0.774V RMS which ÷ 2V peak to peak.
    dBV  where the "0" = 1V RMS about 2.5dB bigger than dBm in 600ê
    dBuV where the "0" = 1uV of signal. e.g. 12dB sinad @ -6dBuV in 75 or 50ê!
    dBvu as displayed on a Voltage Unit meter. 0dBvu=100% level etc.
    dBc  where the "0" = full carrier power. e.g. spurious = -60dBc.
         Not to be confused with the sound dB"C" weighting standard.

In 50 Ohms this is usefull..
Peak    PEP           Peak   PEP
Volts  Watts         Volts  Watts
  2.8   0.08           28      8
  3.3   0.1            33     10
  4     0.16           40     16
  5     0.25           50     25
  5.6   0.32           56     32
  7     0.5            71     50
  8     0.64           80     64
 10      1            100    100
 14      2            141    200
 16     2.5           160    250
 20      4            200    400


See my Buls "QRO 1kW HF Metered Dummy Load" & "QRP Power Meter & Dummy Load"


Why Don't U send an interesting bul?

73 De John, G8MNY @ GB7CIP


Read previous mail | Read next mail


 25.12.2024 20:00:50lGo back Go up