Philips Pm 5326 Bedienungsanleitung Seite 25

Due to the low input impedance of a modern AM receiver, an isolating capacitor of 30 nF must be
connected to i t s IF input. This capacitor must be mounted directly at the end of the cable, a s with
the PM 9072, for example.
I::
- - -
Fig. 3.3-6 Isolating capacitor for low-ohmic signal.supply
For defined signal decoupling with low detuning and damping, a probe with damped resonant circuit
can be used a s attenuator. The coil of this circuit is tapped a t the ratio of 1011, thus transforming
the resonant voltage downward during signal decoupling. The L/C ratio must be optimized for AM-
IF and FM-IF with particular regard to coil losses.
For application in the AM-IF range, for example, the capacitive detuning is eliminated by means of
the trimmer and by tapping the medium and high-ohmic potentials of the test object.
Unit
AM-IF
FM-IF
FM-Tuner
Selectivity
Fig. 3.3-7
Probe with selective voltage divider
via C
33 nF
10 nF
direct
direct
A
f
20 kHz
200 kHz
200 kHz
200 kHz
3.3.4.
Automatic gain control AGC of test object
fwob
50 Hz
50 Hz
50 Hz
IOHZA
To prevent incorrect measurements, it i s necessary to test the efficiency and set-in level of AGC of
the test object. Measuring results obtained at too high levels without suppression of AGC, are subject
to considerable errors. This applies to wobbling, as well a s to static methods.