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Measurement 20dbm + 20 db attenuator, what is the actual power of rf source

user5349
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    If the source is much narrower than the RBW then it's simply 40 dBm. But if the spectrum analyser was set narrower than the source, you have to do some integration over frequency. – tomnexus Oct 06 '15 at 04:06

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40 dBm - 20 dB = 20 dBm

So your input is +40 dBm (10 Watts).

Martin Ewing AA6E
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  • the attenuator added was 20db attenuator, but still the actual power would have been 20dbm+20dbm (?) = 40 dbm. my doubt was attenuator was not of 20dbm, it is of 20db, but still the explanation holds good ? – user5349 Oct 07 '15 at 00:39
  • Yes. "dB" refers to a ratio of power, a 20 dB attenuator reduces power by a factor of 100. "dBm" is a value of power, so 20 dBm is 20 dB above 1 milliwatt, or 100 mw. – Martin Ewing AA6E Oct 07 '15 at 11:58