Tektronix 1L30, Инструкция по эксплуатации

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response is very narrow, so the display resolution is in­
creased as the diode forward bias increases.
Circuit Description— Type 1L30
SW550, the RESOLUTION selector, can be coupled to the
.DISPERSION selector and when so coupled, provides normal
resolution for each position of the DISPERSION selector pro­
vided the sweep rate is not too fast. See Operating section.
However, by pulling the control knob, the RESOLUTION
selector is uncoupled and any desired resolution within the
range of the control can be obtained for a given DISPER­
S IO N selector position.
The 100 kHz Resol Cal adjustment R543 is adjusted for
a resolution bandwidth that is approximately 60 kHz with the
RESOLUTION control at the 2nd position and more than
100 kHz bandwidth with the control fully clockwise. The re­
maining positions of the control decrease the bandwidth
at each successive step in the counterclockwise position.
This provides adequate resolution for most displays.
Emitter followers Q 510-Q 520 isolate the high impedance
of the filter network from the relatively low output imped­
ance, thus minimizing circuit loading on the filter network.
Q530 is a grounded-emitter operational amplifier with a
relatively low output impedance to provide the power re­
quired to drive the Log and Square Law circuits.
Output and Detector
The 5 M H z IF response from the variable resolution am ­
plifier is applied through a bandpass filter circuit to shape
the response and attenuate spurious signals. VERTICAL
DISPLAY switch SW660 selects one of three display modes;
LOG, LIN and SQ LAW. The VIDEO position changes the
display to a time domain display.
The LOG position applies the signal without attenuation
to the amplifier V620. This provides the full dynamic range
required for the LOG diode circuit and a logarithmic dis­
play over the 6 cm graticule height.
The signal is atttenuated by the voltage divider R606-
R607, so that an approximate 4.5 centimeter display in the
LIN position will provide approximately the same signal
amplitude when the switch is changed to either of the other
two positions. , '
In the SQ LAW position, two germanium diodes, D603-
D604 are connected back to back to form a square law
voltage divider. Signal voltage to the amplifier V620 in
the SQ LAW mode becomes a function of the diode's dy­
namic resistance characteristic curve as shown in Fig. 3-9.
Note that diode resistance exceeds 100 kQ for very low
(mV) input signals. The divider ratio is approximately 200:1
' so’ approximately 0.5% of the signal will be applied to
V620. W ith a 150 mV signal, the dynamic resistance of
the diode decreases to approximately 5 kQ, so approxi­
mately 10% of the signal will be applied to V620. The
circuit normally requires about 70 mV signal for full screen
display so the diodes usually operate along the steep slope
of the dynamic resistance curve.
This non-linear dynamic resistance of the divider produces
a display which emphasizes small signal level differences.
The vertical response for the §Q LAW display is, therefore,
approximately proportional to the signal power,
©
Fig. 3-9. Diode characteristic curves.
The. input signal from the VERTICAL DISPLAY selector is
coupled through T610 to the 5 M Hz crystal filter. The series
response characteristic of the crystal determines the band­
pass of this filter circuit. C610 is adjusted to shunt or reduce
the parallel response point of the crystal filter. L620 and
C620 are tuned to 5 MHz. The . circuit shapes the response
of the 5 M Hz IF and attenuates any spurious signals that
may pass through or are generated in the 5 M Hz resolu­
tion circuit.
V620 is a high gain amplifier driving the emitter follower
Q650. This circuit provides the voltage gain and drive re­
quired by the detectors for both the video and recorder
output. L624 tunes the plate circuit to 5 MHz.
The detector diodes D660 and D661, connected as a volt­
age doubler circuit, provide the 40 dB dynamic range for
3 -9