Glenayre Document Number: 9110.01002
GL-T8541 PA
09/10/99
CHECKOUT AND MAINTENANCE
t8541
p7.
fdk
Copyright © 1997 Glenayre
Page: 7-5
7.6.4 Testing the Antenna and its RF Feedline
The RF wattmeter and RF test load can be connected between the output of the isolator and
the antenna to determine the performance of the RF feedline and antenna. Refer to
Figure 7-3 for the test setup. This test is useful if the performance of the antenna system is
suspected, or the isolator or its reject load is becoming excessively hot or failing.
Note
The amplifier RF output power is rated at 250 watts at the PA output connec-
tion. The maximum RF power obtained at the output of the isolator will be
less than 250 watts. Refer to Table 7-1 for a list of isolators and their
maximum RF output power, with the power amplifier operating at 250 watts.
Operate the transmitter at rated power and note the forward and reflected power level indi-
cations on the external wattmeter. Refer to the exciter VDT user manual for transmitter
operating instructions, and to Table 7-1 for the relationship to forward and reflected power
levels and the voltage standing wave ratio (VSWR) of the feedline and antenna. Refer to
the antenna and RF feedline specifications to determine the VSWR and power ratings of
the antenna system. The power amplifier specifies a maximum VSWR of 1.5 to 1, but most
antenna systems will operate at a much lower VSWR. If an isolator is used, the power
amplifier should see a much lower VSWR than that of the antenna system.
The relationship between VSWR, forward power (Fwd) and reflected (Ref) is:
Figure 7-3 Antenna System Test Setup
Table 7-1 Relationship of VSWR to Fwd and Ref Power
VSWR
Ref Power
(Fwd = 230 W)
Ref Power
(Fwd = 220 W)
Ref Power
(Fwd = 210 W)
Ratio Fwd to
Ref Power
1.2 to 1
1.9 watts
1.8 watts
1.7 watts
0.0083
1.5 to 1
9.2 watts
8.8 watts
8.4 watts
0.04
1.925 to 1
23 watts
22 watts
21 watts
0.10
2.0 to 1
26 watts
24 watts
23 watts
0.111
Ref
Fwd
-----------
VSWR
1
–
VSWR
1
+
-------------------------
2
=
VDT
DSP
Exciter
Power
Amplifier
Isolator
RF Wattmeter
Antenna
Antenna
Feedline
Short length of low-loss
RF cable
