Agilent Technologies PSA Series User And Programming Manual page 76

Instrument Functions: A - L
BW/Avg
2.3.5.2 Log-Pwr Avg (Video)
Selects the logarithmic (decibel) scale for all filtering and averaging processes. This scale is
sometimes call "Video" because it is the most common display and analysis scale for the
video signal within a spectrum analyzer. This scale is excellent for finding CW signals near
noise, but its response to noise-like signals is 2.506 dB lower than the average power of
those noise signals. This is compensated for in the Marker Noise function. When this type
of averaging is selected, LgAv appears on the left side of the display.
The equation for trace averaging on the log-pwr scale is shown below, where N is the
number of averages accumulated. (In continuous sweep mode, once N has reached the
Average Number, N stays at that value, providing a running average.)
(
N 1 –
------------------------------------------------------------------ -
New avg =
Assumes all values in decibel scale.
Key Path:
BW/Avg
or
Auto Couple
Remote Command:
See "Avg/VBW Type" on page
Example:
AVER:TYPE LOG
2.3.5.3 Pwr Avg (RMS)
In this average type, all filtering and averaging processes work on the power (the square of
the magnitude) of the signal, instead of its log or envelope voltage. This scale is best for
measuring the true time power of complex signals. This scale is sometimes called RMS
because the resulting voltage is proportional to the square root of the mean of the square of
the voltage. When this type of averaging is selected, PAvg appears on the left side of the
display.
In the equation for averaging on this scale (below), N is the number of averages
accumulated. (In continuous sweep mode, once N has reached the Average Number, N
stays at that value.)
New Avg
Assumes all values in dB.
76
)Oldavg
+ Newdata
N
,
Avg/VBW Type
,
Avg/VBW Type
74.

( ) ×

N 1 –
×
------------------------------------------------------------------------------
= 10 log


Old Avg New data
-------------------- ---------------------- 
10 10

10 + 10

N

Chapter 2