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change. The latter setting is appropriate to measure the time stability of frequency in
short time.
3.6.3 Low pass filter： If the measured frequency is lower and high frequency noise
is included in the measuring of the external signal, there will be the effect of trigger
error resulted from the noise. The measured result will be less accurate with unstable
measured data. The low pass filter with the frequency of 10kHz will be added to the
input signal. The high-frequency noise in the filtering signal does not affect the low-
frequency signal; the measured result will be more accurate. If the frequency of
measured signal is higher, low pass filter will induce amplitude attenuation for the
input signal so as that the measuring sensibility will fall. More badly, correct
measuring result can not be obtained. The low pass filter should be taken out.
For the square signal with low frequency, the low pass filter is not needed
because that the trigger edge is steep and the trigger error is little.
3.7 Parameter calibration（1）
The parameter errors in specification are the indexes when leaving factory. It is
possible to increase for long-time using and large temperature changing. In precision
measurement, the generator should be calibrated. The four parameters of the
instrument can be calibrated in software calibration by the function of calibration.
3.7.1 Code calibrating： Pressing the key of【Menu】 so as to display “----”on the
upper row of the screen, which means the calibration is in the close state. It is
required to input the calibrating code. The standard code 1000 can be input by the
numeric keys and then press 【n】. So 1000 is displayed on the upper row meaning
the calibrating function is in the open state now. Then calibrate as follows.
3.7.2 Calibrating of frequency of channel A： In the state of calibration, press
【Menu】to enable the indicator lights of “CHA” and “Tone”. The calibrating code
of frequency of channel A will be displayed on the upper row. Now the frequency of
channel A is 1MHz. Use the cymometer with the accuracy of over six-digit to
measure the frequency of channel A. At the same time, modify the calibrating code
by the knob. The frequency of channel A will be changed until the accuracy is
calibrated up to 10
-6
. Because the synthesizer of channel B and the synthesizer of
channel A use the same fixed clock reference, the frequency of channel B has the
same accuracy as the frequency of channel A.
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