[1000mp] dB etc

[Ronald Long]

Commenting on various recent posts:

+8dBu is 2.5uV

With a calculator dBu = 20log(uV) where uV is microvolts
and dBu is dB above 1uV

So dBu = 20log(2.5) = +8dBu

We can easily convert dBu to dBm (dB above 1mV) by adding -107 to the dBu 
result

Thus for 50uV (commonly S9)
      first dBu = 20log(50) = 34
      then dBm = -107 + 34 = -73dBm as has been posted.

Another example, if minimum detectable signal is 0.2uV
it can be converted to dBm as follows
      first dBu = 20log(0.2) = -13.98
     then dBm = -107 + (-13.98) = -120.97dBm

All of these assume that the measurements are across the same impedance, 
usually 50 ohms when referring to signal generators and receiver inputs.

ron w8gus