Chapter 6 ______________________________________________________ Processing Algorithms
VAISALA______________________________________________________________________ 237
6.5.3 Treatment of Losses in the
Calibration
In the calibration of the dBm level of the test signal, be sure to account for
any losses that may occur between the antenna feed and the injection point,
and in the cable and coupler that is used to connect the signal generator to
the injection point. Figure 50 on page 236 illustrates the nomenclature of
the various losses that are involved in the calibration. The relationship
between the injected test signal and the value of the received power relative
to the feed is:
For example, assume the following:
Then if the test signal generator output is -50 dBm, the injected power is
The equivalent power at the feed is then 3 dB more than this
During the calibration, there are several ways to handle the losses using
these equations. Two examples are:
- Each signal generator value can be corrected for losses so that the
calibration plot shows IFDR measured power vs received power at the
feed. This is recommended for manual calibration.
- The signal generator values can be plotted directly and the intercept
power I
o
can be corrected for losses so that it is properly referenced to
power at the feed. This is the approach used by the IRIS zauto utility.
Loss between the feed and the coupler dBL
Feed:Coupler
3 dB
Loss caused by the coupler dBL
Coupler
30 dB
Loss in the cable from siggen to
coupler
dBL
Cable
2 dB
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