User's Manual Part 2

Processing Algorithms (draft)
RVP8 User’s Manual
April 2003
5–27
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 5–4 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:
dBm
Feed
+ dBm
Injected
) dBL
Feed:Coupler
dBm
Feed
+ dBm
Siggen
* dBL
Coupler
* dBL
Cable
) dBL
Feed:Coupler
For example, assume the following:
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
Then if the test signal generator output is –50 dBm, the injected power is
dBm
Injected
= –50–[30+2]= –82 dBm.
The equivalent power at the feed is then 3 dB more than this
dBm
Feed
= –82+3 = –79 dBm.
During the calibration, there are several ways to handle the losses using these equations. Two
examples are:
S Each signal generator value can be corrected for losses so that the calibration plot shows IFD
measured power vs received power at the feed. This is recommended for manual calibration.
S 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.