I do not know details of your instrument, but it could be the value of power per unit bandwidth e.g.  dBm/Hz or dBm/MHz. Hence, perhaps you have to integrate spectrum over the frequency in order to get the correct answer - total power of signal. Remember, dBm is logarithmic measure, but to integrate (i.e. make summation) over the spectrum you need to convert values into some linear, namely the power in Watts or milliwatts, etc. Most of instrumental software already have the function of calculating the total power.

Some software analyzers uses power on unit resistance, hence you have V^2/Hz.

When everything went wrong, do read the manual.

In old Linux communities, there was frequently used abbreviation RTFM (read the friendly? manual).

It also depends on the ratio of time, where the signal is ON to the time, where the signal is OFF.

For example:

The signal is ON for 1 second and OFF for 9 seconds.

Then the Peak power is 60 dBm (1000W), but the average power is only 10%, e.g.  100 W.

Dear Dinesh,

The estimate of the total power of a signal spectrum is an operation of integration or summation.

First, you must see if your measurement is to narrowband or wideband.

A measurement is narrowband when you resolve totally all the spectrum components. You can achieve it by reducing the RBW (resolution bandwidth); sweep time reduces as a consequence. In this case you can simply sum the powers relative to the single components of the spectrum of the signal.

If the measurement is wideband, then the situation is more complicate. The estimate of the power of the spectrum must consider the ratio RBW/(fn-fn-1). There are some formulas that you can find in specific books which works very well when RBW>>fn-fn-1. Essentially, the measure of the power of the signal spectrum for wideband measurements where RBW>>fn-fn-1 is close to the concepts expressed by Jacek. However, that method is rigorously suitable for random signal as the noise. In these cases, the Spectrum Analyzer has an internal routine based on the sampling to achieved the total power.

@Gifuni Sir....thanks for your precious time in writing this valuable information. The RBW in our measurement is 20kHz with sweep time 191ms. Could you please suggest me some references/books where can I find expression of the power spectral density for integration?

@Jacek Sir....Thanks for your comment.

Yeah you are right, its dBm/bandwidth. Its power spectral density. Now how to calculate power of the signal? How to find expression for the power spectral density?

@Alexander Sir.....thanks for your valuable comment.

Dear Dinesh,

I attached a pdf file which is useful for you.

Best Regards

Got it....Thanks all of you for your valuable comments and precious time.