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that of carrier signal. The amplitude of exterior signal should be adjusted according
to the requirements of frequency deviation modulation or depth of amplitude
modulation. The larger the amplitude of the exterior modulation signal, the larger the
frequency deviation modulation or depth of amplitude modulation. When using
exterior modulation, the frequency deviation modulation should be set to be 0 and the
interior modulation signal should be closed. Otherwise, the exterior modulation
cannot work properly. Similarly, if using the interior modulation, the value of
“Frequency deviation modulation” should be set and the exterior modulation signal
should be taken out. Otherwise, the operation of interior modulation cannot be
normal.
3.6 Exterior Measurement
Press the key of 【 Count 】 to light up the indicator light of “Count”. The
generator can be used as a cymometer to measure the frequency of the external signal.
3.6.2 Measuring of external frequency： Press the key of 【 Menu】 and the
indicator light of “Hz” will be on. The instrument will be in the state of frequency
measuring. Link the measured external signal from the “Input of exterior measuring”
on the rear panel. The measured signal can be periodic signal of arbitrary waveform.
The Vpp of the signal should be greater than 100mVpp but less than 20Vpp. As the
result includes the effect of crystal oscillating error and triggering error, the accuracy
will be a little worse than those in self-testing.
Linking the end of channel A and the port of “Exterior measuring input” on the back
panel, the generator can measure the frequency for the signal of channel A. Entering
the frequency by the numeric keys or by the knob, the measured result can be
displayed. As the frequency synthesizer of channel A and frequency measuring
instrument use a same clock, the result measured does not include the effect of
crystal oscillation error. So the measured result is of high accuracy.
3.6.2 Setting of gate time： Press the key of 【Menu】 to light up the indicator
light of “Gate”. The gate time will be displayed. The gate time can be entered by the
numeric keys or by the knob. For frequency measuring, the method of averaging the
periods is used. So the longer the gate time is, the more the collected periods is, the
more the effective digits for the measured result, but the slower the tracking velocity
of frequency change. Contrarily, the shorter the strobe time, the less the effective
digits for the measured result, but the faster the tracking velocity of frequency
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