Operating Principle - Philips Pm 5326 Bedienungsanleitung

1.4. OPERATING PRINCIPLE (FIG. 1)
1.4.1. RF circuitry, amplitude modulation
The RF Generator produces the high frequency. The RF FREQUENCY RANGE push-button array
allows selecting the desired range, while the continuous contro! FREQUENCY SETTING determines
the exact frequency.
Via Switching Stage and Amplifier 1 the RF frequency is fed to the Amplitude Modulator passing eihter
unmodulated or amplitude-modulated by the internal 1 kHz Oscillator or by extern MOD IN low fre-
quency due to the selected push-buttons MODULATION.
The amplitude of the RF frequency is stabilized in the control circuit Amplitude with automatic gain
control= in the feedback path.
The Output Amplifier can be interacted by the Output blankinkstage: when sweeping with the internal
triangle the RF-signal is blanked during fly-back.
The RF ATTENUATION sets the output continuously from 0 to -80 dB, but the RF attenuator over-
more has two fixed stages of -3 dB and -40 dB.
1.4.2. Sweep section and frequency modulation
The LF Sweep Generator produces and modulates high frequencies for the sweep ranges .4/.5, 10/11,
36/41, 7511 10 MHz, selected by push-buttons RF SWEEP RANGE. The waveform is semi-rectangular.
The carrier for the frequency modulation and the center frequency for the wobbulating ranges respec-
tively are set in Frequency Selection, activated by RF SWEEP RANGE just mentioned and coarse and fine
adjusted by the double continuous control RF CENTER.
Pressed button AMIFM activates frequency modulation of the ranges 1011 1 or 7511 10 MHz with 1 kHz
internal or with external signal via MOD IN input socket.
I f one of the RF SWEEP RANGE buttons i s pressed, the frequency modulated or wobbulated high
frequency is fed via the Switching Stage to the main RF output path.
Due to the different frequency ranges the maximum sweep width is adapted by RF SWEEP RANGE.
Control RF WIDTH reduces the width.
The sweeping or wobbulating signal and the signal for X-deflexion of an indicator or oscilloscope at the
MODISWEEP OUT socket can be switched off by push-button SWEEP OFFION. I n this case the modu-
lating signal is available at the output.
1.4.3. Frequency marker
The Marker Mixer superimposes the frequency of the RF Generator t o the swept frequency of the RF
Sweep Generator. The low frequency beat is filtered in the Band-pass Filter Amplifier 3 and fed to
the OUT-Y-IN socket for the Y-channel of an indicator (oscilloscope). Each frequency of the RF Gene-
rator can be used for frequency marker, i. e. "travelling marker".
Pulling the button MARKER AMPL generates fixed markers with many harmonics. The fundamental
wave of the fixed marker is selected by RF SWEEP RANGE. So a marker spectrum with suited distance
due to the sweep range i s generated.
When using triangular sweep mode the square wave output of the LF Sweep Generator blanks the fre-
quency markers in the Marker blanking-during fly-back.
1.4.4.
Display circuitry
The frequency of the RF-Generator is divided depending on the selected frequency range and fed to the
Counter Decoder Driver which is controlled by the Time Base. The Time base, i. e. one measuring period
for the counter, i s changed by the chosen frequency range. The stage of the counter at the end of one
measuring period represents the frequency which is multiplex-displayed on the 5-digit display.
Push-button COUNTER EXT enables the display circuitry working a s normal counter. Amplifier 5 feeds
the signal at the COUNTER IN socket directly to the counter, decoder and driver.
1.4.5. Power supply
The -power suppb. provides the stabilized DC voltages of +5 V, + I 2 V, -12 V and +27 V, and the
sinusoidal wobbulating voltage.