wideband signal power

[karote]

Hi

In case I have 10 MHz wide RF signal and I have measured the power level with spectrum analyzer (RBW=100 kHz), so what is the total signal power? The signal power level in the spectrum analyzer screen is -30 dBm.

Can anyone explain this explicitly?

 

[yendori]

I noticed nobody answered your question yet, so I thought I could look busy at and answer it for you.

There is a couple of ways to do this.

#1 Convert you measurment into a 1Hz bw. The spectrum analyzer measured power in bandwidths in your case 100KHz. We need to convert this to 1Hz and then multiply by 10 million (10MHz).

So take 10LOG(100KHz) = 50. So reducing the RBW from 100KHz to 1Hz will reduce the measurment by 50. You measured -30dB, so -30-50 = -80dB.

Now you need to convert -80dB into real "power":
10^(dB/10) =10^(-80/10)=.01microWatts. So it's .01uW per Hz.
The Bandwidth is 10MHz So 10,000,000 x .00000001 = 100mW = 10LOG(.1)=-10dB

-80dB in a 100KHz = -10dB in a 10MHz bandwidth

#2 Another way is to just convert -30dB into power 10^-3 =.001 The divide 10MHz by 100KHz = 100. Then multiply .001 by 100 =.1. That's your actual power in the 10MHz BW. 10LOG(.1) -10dB.

Thank you, my boss thinks I am really busy now.