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8
1.4. Description
of the block diagram
The frequency
of the generator
is determined
by an HF-oscillator
the amplitude
of which is electronically
stabilised. Frequency
rs.1ges are selected with push-button
MHz. With in the selected range the frequency
can
be adjusted continuously
by control F REOUENCY.
A frequency-modulator
provides voltage-controlled
frequency modulation
ot the HF-oscillator·
e.g. for
wobbulating
purposes·
in the ranges 75 MHz ... 110 MHz, 0.4 MHz ... 0.5 MHz and 10.3 MHz ... 11.1 MHz
(/\IVV).
In the amplitude-modulator
the amplitude
of the HF-signal can be modulated
in all frequency
ranges and the
HF-signal blanked during fly-back at mode WOB
VV).
The HF-output
stage amplifies the power of the HF-signal, the amplitude
of which is adjustable continuously
with attenuator
HF AMPLITUDE.
The output signal is available at connector
HF OUT; the output impedance
amounts to 75
n.
If button CAL. is pressed an X.tal controlled
calibration
oscillator produces harmonics
to check the
calibration
of the scale. The markers are at a distance of 10 MHz, 1 MHz or 0.1 MHz, depending
on the
selected frequency
range.
In the mixer the signals of the HF-output
stage and of the calibration
oscillator are mixed. The low-frequency
signal which is obtained at approximately
equal frequencies of both signals is amplified,
limited, rectified and
indicated by a moving coil meter. If the HF-frequency
control is set at a calibration
frequency,
the indicator,
at exactly equal frequencies,
indicates a sharp, limited minimum between two tull scales.
(Fig.
l).
A 1 k+iz-sine wave signal, produced by a 1 kHz oscillator, is used for amplitude·
or frequency
modulation
and selected by push-buttons
AM or FM. The 1 kHz signal is also available at connector
1 kHz/SWEEP OlJT
if button WOB has not been depressed.
If button AM EXT. or FM EXT. has been depressed
the HF-signal can
be modulated
by an external signal supplied to connector
LF IN.
If button WOB has been depressed, a saw-tooth signal, produced by a saw-tooth generator,
is supplied to the
frequency
modulator.
The sweep of the frequency can be adjusted by potentiometer
SWEEP WIDTH. At the
same time the saw-tooth signal with constant amplitude
is available at connector
1 kHz/SWEEP OUT.
A square-wave pulse derived from the saw-tooth signal blanks the output stage dur mg tlv-back.
The supply section delivers two stabilised direct voltages (-12 V and
-18
VI and an alternating
voltage for
illumination
of the scale.
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