INTRODUCTION
The B & K-PRECISION Model
1820
80 MHz Universal
Counter is
a high quality, lightweight, autoranging frequency
Counter.
It measures frequencies in the range of 5 Hz to 80 MHz. In
addition, the Model
1820 is capable of measuring the period
required for one cycle to occur, accumulated cycles and
time. The functions of the
Counter are selected by the four
FUNCTION pushbutton switches on the front panel. When the
ACCU (accumulate) or TIME function is selected, the display
may be reset to ZERO by momentarily depressing the RESET
pushbutton.
The AUTO/1 SEC (100 period average) switch selects either a
one-second preset gate interval or the “AUTO” range. When
the switch is in the “AUTO” position (out) the gate interval
or period average that allows maximum resolution without
overranging is automatically determined and the appropriate
frequency/ time unit indicator for either KHz/juS or MHz/mS
is illuminated. When the AUTO/1 SEC pushbutton is in the 1
SEC (depressed) position, the display indicates frequency to
the closest hertz or period to the nearest nanosecond even
if the most significant digit (MSD) is beyond the display range.
When the X1/X10 pushbutton is in the XI position (out), the
input signal is applied to the
Counter circuits without
attenuation. However, when the switch is depressed, the
input signal is routed through an X10 attenuator before
being applied to the
Counter circuitry.
When a function switch is pressed the first time, it locks
in the “in” position. When another function pushbutton is
pressed, all other function pushbuttons return to the “out”
position.
The RESET pushbutton is a spring-loaded momentary contact
switch that is independent of all other pushbuttons.
The standard input impedance of one megohm in conjunction
with a ten-to-one scope
Probe makes this instrument ideal
for use in applications where source loading must be kept to
a minimum.
The display consists of six seven-segment light emitting
diode (LED) numerical display units and three LED’s to
indicate KHz//xS, MHz/mS and OVER (overrange).
The internal 10MHz time base is generated by a crystal
controlled
Oscillator. However, it may be desirable to use
an external time base for certain
Counter applications.
Consequently, the EXTERNAL TIME BASE INPUT connector has
been included. This female BNC jack, on the rear panel,
provides a convenient means of connecting the external time
base to the
Counter. In addition, the TIME BASE SELECT
switch, also on the rear panel, allows the user to select
either the internal or external time base.
The optional Temperature Compensated Crystal
Oscillator
(TCXO) is available for use as an internal time base with
the Model
1820, The TCXO is a highly stable
crystal-controlled
Oscillator that produces a closely
controlled time base frequency over a wide temperature
range. When the TCXO is used with the
Counter, the TCXO
replaces the original time base
Generator in the
1820, The
TCXO may be installed by the user.
The exceptional accuracy of the
Counter makes it an
extremely valuable instrument to the scientist, engineer and
experimenter. Its ruggedness and compactness make it
practical for use by the hobbyist or in the field by service
technicians. The low power consumption of less than 15 watts
makes it practical to power the
Counter by a DC-to-AC power
converter.
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