Philips PM 5326 Instruction Manual page 28

3.3.5.4.
Adjusting overcritical coupled band filters
The mostly overcritical coupled band filters in the FM-.IF amplifier must be damped and adjusted
alternately. The connection wires of the damping resistor should be as short as possible.
Indicator
Fig. 3.3-1 1 Adjusting overcritical coupled IF band filters
Repeat the adjustment of a band filter several times.
3.3.5.5. Symmetry of a ratio detector
The S-shaped demodulator characteristic (fig. 3.3-17) should be linear and symmetric to the zero-axis
crossing with normal control. For determining the symmetry,
i t is convenient to adjust the
ratio
detector in amplitude limitation
.
The rectified voltage a t the limiter capacitor C2 is halved in the vol-
age divider and is symmetricalwith refence to the LF demodulator output (fig. 3.3-12). For recording
the s-shaped demodulator characteristic, supply the signal to the base of the last IF stage.
R 1
U
n
R 6
10k
Y
n
Fig. 3.3-12
Adjusting the symmetry of a ratio detector
3.3.6.
Examples of wobbling
3.3.6.1. Test setup for checking and adjusting an FM receiver
see fig. 3.3-13. Examples of oscillograms are shown in figs.
5 and 6. The centre frequency in the FM-IF