Chapter 2 Design and Function
5300.9677.72 - 2.26 - EN-4
Power reduction of FM transmitter with VSWR
If the transmitter is operated with mismatched load at a VSWR > 1.5, the transmitter should
not be shut down completely but instead should continue to operate with reduced power. In
this case, the power should be reduced in such a way that amplifiers or absorbers are not
subjected to a thermal or electrical overload.
If the VSWR value exceeds 1.55, the output power is reduced in line with the following for-
mula:
P
forward
= P
nominal
/ VSWR
To prevent uncontrolled fluctuation of the output power at a VSWR of 1.5, the (VSWR-de-
pendent) power reduction is not canceled until the VSWR value has dropped below 1.45
again (hysteresis).
2.1.7 Protection against Overvoltages from the Antenna Cable
An inductance to ground is located in the output of each amplifier. This inductance diverts
overvoltages. The solution comes under lightning protection category III and cannot be
used as the only lightning protection device for the antenna.
Note The transmitter is intended for use in lightning protection zone III (location within a building).
The measures to provide protection for zones I and II must be provided by the customer.
Electrical connection of
operating voltage to inner
conductor of RF output
Capacitive coupling within RF ampli-
fier output circuit
No connection
Fault Protection mechanism Function
Overvoltage Short-circuit coil in harmonics filter of
RF amplifier
Shunting of overvolt-
age
Fault Protection mechanism Function
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