FUNCTIONAL DESCRIPTION
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DESCRIPTION OF NORMARC 2-FREQUENCY TRANSMITTER
1
Functional Description
The transmitter section generates the ILS signal with the required RF power levels and modu-
lations levels. The section comprises two identical transmitters, TX 1 and TX 2, where one is
connected to the antenna, while the other is connected to dummy loads, acting as a back-up.
The reference signals in the transmitter section are RF signals from the oscillator OS1221AB
and LF modulation signals (90Hz and 150Hz) from the low frequency generator LF1223A.
System DC voltages comes from the Power Supply board PS1227A.
In each transmitter, the RF oscillator has separate outputs for Course and Clearance. These
two channels are offset by 10 kHz. The LF Generator also has independent outputs for
Course and Clearance. Clearence transmitter is however not included in this single frequency
equipment.
The GPA 1231A Glidepath Course Power Amplifier Assembly contains modules to modulate,
amplify and combine signals into the required CSB and SBO signals. Amplitude- and RF
phase feedback ensures correct RF power level and modulation.
The Clearance transmitters GPA1232A generate only CSB signals, and only amplitude feed-
back is therefore incorporated.
The COA 1207A/C Change Over section has relays to connect the CSB and SBO outputs
from one transmitter to the antenna while the other is connected to dummy loads. The relays
are controlled by a Coax-control signal. SBO phase shifters and attenuators are incorporated
for obtaining the correct CSB/SBO relationship.
The block diagram is shown on the next page.
