e. Usually the output of the generator contains a calibrated attenuator and
often an output level meter.
The output level meter gives an indication of, and
permits control of, the output voltage of the generator by indicating arbitrary
values of output readings in tenths through the value of one.
The attenuator
selects the amount of this output. The attenuator, a group of resistors forming a
voltage-dropping circuit, is controlled by a knob which is calibrated in
microvolts. When the control element is adjusted so the output meter reads unity
(1.0), the reading on the attenuator knob gives the exact value of the output in
microvolts. If output voltage is desired at a lower value, the control is varied
until the meter indicates some decimal value less than one, and this decimal is
multiplied by the attenuator reading to give the output in microvolts.
7.
Frequency-modulated RF signal generators.
Frequency-modulated RF signal
generators are widely used for testing frequency-modulated receivers and for visual
alignment of AM receivers. A frequency-modulated signal is an alternating voltage
in which the frequency varies above and below a given center frequency value. The
overall frequency change is called the frequency swing.
Learning Event 3:
DETERMINE THE DIFFERENT MODES OF AN ELECTRONIC COUNTER
1.
An electronic counter is used for the comparison of an unknown frequency or
time interval with a known frequency or time interval.
The counter's logic is
designed to present this information in an easy-to-read numerical display.
The
accuracy of this measurement depends on the stability of the known frequency. This
known frequency is obtained from the internal oscillator of the counter.
2.
The logic control interconnects the proper circuit, selects
the
proper
measurement units for display, and starts the measurement cycle.
a. An electronic counter can be operated in the totalizing mode with the main
gate flip-flop controlled by the manual start-stop switch illustrated in Figure 3-
4.
With the switch at start, the decimal counter assemblies totalize the input
pulses until the main gate is closed by changing the switch to stop. The display
on the counter shows the pulses received during the interval between manual start
and manual stop.
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