Vaisala RVP900 User Manual

USER’S MANUAL__________________________________________________________________
236 _________________________________________________________________ M211322EN-D
Finally turn it all the way down and make one more sample to measure the
noise level N. I
o
is obtained from the intercept of the horizontal line at N
and the straight line fit to the linear portion of the curve. This value must
be corrected for losses as discussed in the section below.
6.5.2 Single-Point Direct Method for
Calibration of Io
This calibration method requires no support software. The approach uses
the TTY setups commands. Again the signal generator output must be
calibrated in absolute dBm. Use a power meter to check the calibration.
- Turn the radiate off and connect the signal generator to the test signal
injection point.
- Raise the antenna to at least 20 degrees, and set the azimuth to point
away from any known RF sources including the sun.
- Select the pulse width using the mt command.
- Select the pr command and use the commands to set the following:
Plotting Received Power Spectrum...
Rx:Pri, Zoom:x1-x8, Navg:25, Start:100.01 usec (14.99
km), Span:50 usec
- Set the signal generator to the approximate radar RF frequency with a
power level corresponding to a strong signal (30 dB above the noise),
and use a CW signal (not a pulse). This signal should be visible as a
peak in the spectrum display. Adjust the siggen RF signal frequency
so that produces the precise IF frequency (for example, IF frequency
of 30 MHz).
- Turn the signal generator off and record the "Filtered" power level.
Note that because of the large averaging it will require several seconds
for the average to stabilize.
- Turn the signal generator on, verify that the peak is still at the IF
frequency and adjust the power level to obtain precisely 3 dB more
"Filtered" power than was observed with the noise only. Again, allow
several seconds for the averaging to stabilize after you make each
amplitude adjustment.
This is the value of I
o
, that is, the test signal signal power equals the noise
power. The next step is to correct the value of I
o
for losses (see Section
6.5.3 Treatment of Losses in the Calibration on page 235).

Vaisala RVP900 Specifications

General

Brand	Vaisala
Model	RVP900
Category	Receiver
Language	English