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

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    $\begingroup$ 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. $\endgroup$ – tomnexus Oct 6 '15 at 4:06
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40 dBm - 20 dB = 20 dBm

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

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  • $\begingroup$ 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 ? $\endgroup$ – user5349 Oct 7 '15 at 0:39
  • $\begingroup$ 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. $\endgroup$ – Martin Ewing AA6E Oct 7 '15 at 11:58

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