# Calculating the power spectral density on a different bandwidth

Let us say I have the power spectral density for a given bandwidth F1 at a transmit power T. I would like to calculate the power spectral density for bandwidth F2 for 1) the same transmit power T 2) for different transmit power T2

How can I calculate this

For ex: Let's say I am looking at the spectrum of an OFDM signal in the baseband with a BW of 20Mhz transmitting at power of 23dbm and i know the power spectrum of this signal. Now I would like to derive the power spectrum of the OFDM baseband signal with a BW of 10MHz transmitted at the same power

• The spectral density in different frequencies is orthogonal (no relation between one to another). Consider x= asin(t) + bsin(5t). Knowing 'a' does not help you finding 'b'. – Gideon Genadi Kogan Jan 29 at 5:43
• I am not referring to a different frequency but a different bandwidth on the same center frequency – Dsp guy sam Jan 29 at 7:42
• Say in the first bandwidth the angular frequency of 5 was out of the bandwidth and in the second bandwidth it is in... – Gideon Genadi Kogan Jan 29 at 7:46
• Let's say I am looking at the spectrum of an OFDM signal in the baseband with a BW of 20Mhz transmitting at power of 23dbm and i know the power spectrum of this signal. Now I would like to derive the power spectrum of the OFDM baseband signal with a BW of 10MHz transmitted at the same power, do you suggest this is not derivable? – Dsp guy sam Jan 29 at 8:40
• No, I suggest putting all this newly presented information into the question. – Gideon Genadi Kogan Jan 30 at 6:15