Structure of DTV Networks and Transmitting Stations - Digital Video and Audio Broadcasting Technology - page 533

already "pre-equalized" via the exciter, i.e. the characteristic is simulated
in the equalizer and used for comparison.
In principle, a class AB amplifier consists of a push-pull stage which is
set by the quiescent current of the transistor in such a way that the transfer
distortion is already minimized. The transistor supply voltage is about
30 V.
To build up a power amplifier module, the input signal is first amplified
from approx. 0 dBm to a reasonable order of magnitude and then split with
the correct power and phase over a number of 3 dB couplers and supplied
to the respective individual amplifiers. The output powers of the individual
amplifiers are then combined again and again via 3 dB couplers to form
the total output signal of an amplifier module. The average total power of
an power amplifier module is then approx. 450 W. Then the power ampli-
fier modules are coupled together building a power amplifier unit.
Fig. 31.8. Principle of a power amplifier module for VHF or UHF
31.3.1.2 Mask Filter
The mask can be implemented as uncritical or critical mask, depending on
the requirements of the relevant regulating authorities. In the case of the
Mt. Wendelstein and Olympic Tower transmitters, they are filters with
critical mask, i.e. the "shoulder" of the DVB-T signal must be lower than
more than 51 dB in the adjacent channel. The manufacturer of these filters
is the company Spinner in Munich. The filters are so-called dual mode fil-
ters. The filters are passive mechanical cavity resonators and are relatively