Vaisala RVP900 User Manual

USER’S MANUAL__________________________________________________________________
234 _________________________________________________________________ M211322EN-D
0916-061
Figure 49 Model Intensity Curve
6.5.1 Plot Method for Calibration of I
o
This approach generates the curve shown above (red) which determines the
value of I
o
. The general procedure is to connect a calibrated signal
generator to the radar receiver and inject known power levels to generate a
calibration plot of measured power vs the inserted power at the antenna
feed, similar to that in Figure 49 on page 232. The calibration reflectivity
dBZ
o
is computed from the radar constant and the value of I
o
, which is the
intercept of the straight line fit (green) with the Noise level.
Why does this geometric construction yield the value of I
o
? Let G
dB
represent the overall gain of the RF and IF components leading up to the
RVP900. The green line can be interpreted as the response of an ideal
noise-free amplifier having gain GdB , while the red curve is the response
of the real-world amplifier(s) whose equivalent front-end noise is I
o
:
The measured receiver noise is the horizontal asymptote of the red curve,
that is, the value of the red curve when the input power P
IN
is zero:
RVP8 Measured Power (2dB per Major Div)
Power at Antenna Feed (2dB per Major Division)
1.2dB Detection
Threshold (LOG)
10Log(I
o
)
–5dB SNR
Min Detectable
10Log(N)
Red 10log
10
P
OUT
G
dB
10log
10
P
IN
I
0
++=
Green 10log
10
P
OUT
G
dB
10log
10
P
IN
+=

Vaisala RVP900 Specifications

General

Brand	Vaisala
Model	RVP900
Category	Receiver
Language	English