# Question about an HP 8560 E-Series and EC-Series

Question asked by jevrarulb on Apr 19, 2011
Hello

I am a new user of spectrum analysers (i work with a HP 8565E)  and i have some question about his utilisation. I hope that this topic are in the good section and i am sorry for my english it is not my mother tongue .

Question :

1) Why the level amplitude is a function of the resolution bandwitdth (RBW) ?

example : if i am in LINEAR amplitude (µvolts) and i place a MKA (marker) at the center frequency (CF) 500MHz, for example, with a
RBW = 1MHz, i have MKA = 252.2µV and at the same CF for the same signal but with a RBW = 300kHz, i have MKR = 138.4µV. The relation between the two values is : 252.2µV x Sqrt[RBW]  = 252.2µV x Sqrt[300/1000] = 252.2µV x 0.5477 = 138.4µV ??????????

2) The spectrum analyser display the power spectral density in Volts^2/Hz or in Watt/Hz (I think???) but why in the scope the amplitude axis are in dBm,dBµV,...  with de log mode and µV,mV, mW,... for the linear mode . How the spectrum analyser convert V^2/Hz in mV, where the RBW is use ????

3) If i want to mesure the totale power between two frequency, example for a white noise signal, i want to calculate the total power between 5MHz and 10Mhz with a RBW=300kHz. The amplitude are in LINEAR (i can not use de dBm) mode with milliVolts units and i will the total power (pwtot) : which formule have i to use ?  pwtot = Sqrt[SUM ( (amplitude_i(mV))^2 )] where amplitude_i hare the differents amplitude of the signal between 5-10MHz , the RBW or the bandwidth (5MHz) hare not use is it normal ?????

thanks