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3.3.4
3.3.5
symmetry within the 75 kHz deviation. In the case of receivers with an AM sup-
pression trimmer, adjust the trimmer with maximum
RF signal for maximum
AM
suppression, afterwards align the secondary circuit with a low RF input signal for
optimum linearity and symmetry.
Signal modulation (modulation selection
to 4kHz/60 %) will also display the
level of AM suppression.
The band width of a curve display can be measured as follows: Using the mean
frequency of 10.7 MHz, select a point approximately
in the middle of the curve
display under consideration and note its horizontal position, e. g. the vertical point
of the screen
co-ordinates
(Fig. 4). Now
shift the end points of the curve
by
detuning the frequency
@® into the position noted, e.g. into the verticals of
the screen co-ordinates and read off the two frequencies so found (figs. 5 and 6).
The difference of the two frequencies is the band width of the curve investigated.
AM Alignment for LW, MW and SW
The AM/FM generator AS 4B
is amplitude modulated with 1 kHz or 4 kHz @ and
is connected through the connecting cable 6046 B and the artificial aerial 6045 to the
aerial
input of the radio receiver. An output meter or an AC valve voltmeter,
connected
parallel to the loudspeaker speech coil, is used as tuning indicator.
The range switch @ selects the range required and the rotary control
selects
the required frequency.
The radio volume
control is set to maximum
and the RF output signal of the
AM/FM generator is retarded as far as possible by @ and ©.
In the absence
of more
accurate
service
instructions,
the pre- and oscillator-
circuits are aligned close to the scale end points. Coils are always adjusted with
the tuning condenser
almost set to maximum
capacity (e.g. 600 kHz), trimmers
are adjusted with the tuning condenser set to almost minimum
capacity (e.g. at
1200 kHz) until maximum
deflection
of the output
meter
or valve voltmeter
is
shown.
Repeat the alignment a few times and finish with the alignment of the
trimmers.
VHF/FM-Alignment
The AM/FM
generator
is frequency
modulated
at 1kHz
or 4kHz
and
is
connected through the wide band balun SU 624 D to the aerial input sockets of
the radio receiver. An output meter or an AC valve voltmeter, connected parallel to
the loudspeaker speech coil, is used as tuning meter. The range switch @ is set
to range 12 and the rotary control
is set to the required frequency.
Turn the radio volume control to maximum.
If no exact service
information is available, align the oscillator and intermediate
circuits as follows
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