NORMARC 7033, Руководство пользователя

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DETAILED DESCRIPTION
NORMARC 7033
2-21
INSTRUMENT LANDING SYSTEM
TRANSMITTER DESCRIPTION
©1999 Navia Aviation AS
The lowpass filter at the output is a 7th order filter, giving better than 50dB attenuation of all
harmonics and forward loss is less than 0.5dB. Filter input and output impedance are 50
Ω
.
2.4.3 AC1226A Amplitude control
General Description :
The main purpose of the AC1226A is to maintain a constant modulation and RF level for the
output signals from the PA 1234A power amplifiers. The RF level and modulation depths are
derived from three reference input signals coming from LF 1233A. A DC reference level sets
the RF level for both power amplifiers and one 90Hz and one 150Hz AC reference signal
determines the modulation depths of the 90Hz and 150Hz power amplifiers respectively. The
AC1226A also contains measurement circuits for the RMS.
ADJUSTMENTS:
The levels of the reference DC signal and the two reference AC signals are separately adjust-
able. In addition, the power balance between the two power amplifiers can be adjusted. The
goal of these adjustments is to compensate various tolerances inside the GPA1231A.
Adjusted correctly, any GPA1231A can be replaced by any other GPA1231A without any
adjustments, and still be within specified limits.
Any site or RF frequency dependent adjustments shall be made on the LF1223A module via
the RMS system.
FEEDBACK FUNCTION:
The 90 and 150 Hz LF signals from LF1233A are combined with the DC (ident) signal also
coming from LF1233A to form the desired RF envelope for each of the PA1234A. This enve-
lope is compared with the envelope detected by FD1236A and the resulting signal is fed to the
PA1234A modulator. This process eliminates any ground offset between the GPA1231A and
the LF1223A generating the reference signals.
MAINTENANCE MEASUREMENTS:
Following measurements are reported to the RMS:
The 22-28V DC power supply for each PA1234A.
Detected CSB and SBO RF level.
Peak of the phase correction curve.
2.4.4 PC1225B Phase Control
General Description:
The RF carrier signal from OS1221B (Ch. 2.3) is split in two paths, one to be modulated with
150 Hz, and one to be modulated with 90 Hz. The first stage of each path is a phase regulator,
with a range of ±100 degrees. In the 90Hz path, the phase is set with a potentiometer for ref-
erence, in the 150Hz path the phase is controlled by a phase comparator. The phase compar-
ator is a part of a negative feedback loop which ensures the correct phase relationship
between the 90Hz and 150Hz modulated RF signals from the PA1234A power amplifiers prior
to combining them into CBS and SBO. Each of the phase regulators is followed by a buffer
amplifier, a 15dB gain block and a output stage.
The RF level at the output is fed back in an automatic gain control feedback loop ensuring
constant output level of 20dBm.
2.4.5 FD1236A Feedback Detector