Description Of The Block Diagram - Philips PM5324 Instruction Manual

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1.4. Description of the block diagram

The frequency of the generator is determined by an HF-oscil l ator the ampl i tude of wh ich is e l ectronica l ly
sta b i l ised. Frequency ranges are selected with push-bu tton MHz. W i th in the sel ected range the frequency can
be adjusted continuously by control FREQUENCY.
A frequency-modu l ator provides vol tage-control l ed frequency m od u l ation
wobbulating purposes - in the ranges 7 5 MHz
(/\/V'v).
In the amplitude-mod u l ator the ampl i tude of the HF-s ignal can be mod u l ated in a l l frequency ranges and the
HF-signal blanked d u r ing fly-back at mode WOB
The HF-output stage ampl ifies the power of the HF-s ignal, the amplitude of wh ich is adjustab l e continuously
with attenuator HF AMPL ITUDE.
T he output � ignal is ava i lable at connector H F OUT; the output impedance amounts to 7 5 D_
If button CAL. is pressed an X-tal controlled cal ibration oscillator produces harmonics to ch eck the
ca l i bration of the sca l e. The markers are at a distance of 10 MHz, 1 MHz or 0. 1 MHz, depending on the
sel ected frequency range.
In the m ixer the s igna ls of the HF-output stage and of the calibration osc i l lator are m ixed. The l ow-frequency
s igna l which is obta ined at approx i mately equ a l frequencies of both signals is ampl ified, l i m ited, rectified and
indicated by a moving co i l meter. If the HF-frequency contro l is set at a cal ibration frequency, the ind icator,
at exactly equal frequenc ies, indicates a sharp, l i m ited m inimu m between two fu l l sca l es. (Fig.
A 1 kHz-s ine wave s ignal, produced by a 1 kHz osc i l lator, is used for a m p l i tude- or frequency modu lation
and sel ected by push-buttons AM or F M. The 1 kHz s igna: is a lso ava i l a b l e at connector 1 kHz/SWEEP OUT
if button WOB has not been depressed. If bu tton AM EXT. or F M EXT. h as been depressed the H F-signal can
be mod u lated by an external sign a l supp l ied to connector LF IN.
If button WOB has been depressed, a saw-tooth s ignal, produced by
frequency modulator. The sweep of the frequency can be adjusted by potent iometer SWEEP W IDTH. At the
same t i me the saw-tooth s igna l with constant ampl i tude is avai l a b l e at connector 1 kHz/SWEEP OUT.
A square-wave pu lse derived from the saw-tooth s ignal blanks the output stage d u r ing f l y-back.
The supply section delivers two stabi l ised direct vol tages (-12 V and -18 V) and an a l te rnating vol tage for
i llumination of the sca l e.
of
1 10 MHz, 0.4 MHz ... 0. 5 MHz and 10.3 MHz
. _ .
(/V).
a
saw-tooth generator, is supplied to the
the HF-osci llator - e.g. for
.. 11.1 MHz
.
1).