DK8KW Longwave Information
dBm to dBu to Voltage and to S-units

As more of us use selective level meters to receive the longwave band, I have put up this list that enables to convert from dBm to Voltage in mV or uV and to S-units, to get an idea about the signal strengths measured with various receivers. For conversion of dBu to dBµV/m for my receiving setup, have a look here.
 

 
dBm
(R = 50 Ohm)
dBu*  
( R= 75 Ohm,   
0 dbu= 0.775 V) 
 
Voltage
S-units   
(S9=100 uV, R=50 Ohm)
S-units
(S9=50uV, 
R=50 Ohm)
- 7 dBm - 17 dBu 99.88 mV S9+60  
-13 dBm
- 23 dBu
50.06 mV 
 
S9+60
- 17 dBm - 27 dBu 31.58 mV S9+50  
-23 dBm 
- 33 dBu
15.83 mV 
 
S9+50
- 27 dBm - 37 dBu 9.99 mV S9+40  
- 33 dBm
-43 dBu
5.01 mV
 
S9+40
- 37 dBm -47 dBu 3.16 mV S9+30  
-43 dBm
-53 dBu
1.58 mV
 
S9+30
- 47 dBm -57 dBu 1.00 mV S9+20  
-53 dBm
- 63 dBu
500.59 uV
 
S9+20
- 57 dBm - 67 dBu 315.85 uV S9+10  
-63 dBm
- 73 dBu
158.30 uV
 
S9+10
-67 dBm - 77 dBu 100 uV S9  
-73 dBm
- 83 dBu
50.00 uV
S8
S9
- 79 dBm
- 89 dBu
25.01 uV
S7
S8
- 85 dBm
- 95 dBu
12.58 uV
S6
S7
- 91 dBm
- 101 dBu
6.30 uV
S5
S6
- 97 dBm
- 107 dBu
3.16 uV
S4
S5
- 103 dBm
- 113 dBu
1.58 uV
S3
S4
- 109 dBm
- 119 dBu
0.79 uV
S2
S3
- 115 dBm
- 125 dBu
0.40 uV
S1
S2
- 121 dBm
- 131 dBu
0.20 uV
S0
S1
- 127 dBm - 137 dBu 0.10 uV   S0
 
 
 * When I give any signal strength measured with my MV61 or MV62, I give this strength in -dBu(75)
 

Some further explanations:

Decibel (dB): Equal to one-tenth of a bel (After Alexander Graham Bell) The preferred
method and term for representing the ratio of different audio or rf levels. It is a mathematical
shorthand that uses logarithms (a shortcut using the powers of 10 to represent the actual number)
to reduce the size of the number. For example, instead of saying the dynamic range is 32,000 to 1,
we say it is 90 dB [the answer in dB equals 20 log x/y, where x and y are the different signal
levels]. Being a ratio, decibels have no units. Everything is relative. Since it is relative, then it
must be relative to some 0 dB reference point. To distinguish between reference points a suffix
letter is added as follows:

0 dBu A voltage reference point equal to 0.775 Vrms. This reference originally was labelled dBv (lower-case) but was too often confused with dBV (upper-case), so it was changed to dBu (for unterminated).
 
0 dBm A power reference point equal to 1 milliwatt. To convert into an equivalent voltage level, the impedance must be specified. For example, 0 dBm into 600 ohms gives an equivalent voltage level of 0.775 V, or 0 dBu (see above); however, 0 dBm into 50 ohms, for instance, yields an equivalent voltage of 0.224 V.
 


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