Racal Instruments 3152A, Руководство пользователя

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3152A User Manual
Racal Instruments
©
2001 Using The Instrument 3-49
Using the
Frequency
Counter
In PLL mode, the Model 3152A uses an autoranging counter
circuit to measure frequencies of reference signals at the trigger
input. This built-in counter is made available to you as long as
the signal at the trigger input is valid and the PLL ON LED
illuminates. Frequencies are measured from 500Hz to 10MHz
with 4 digit resolution.
To measure external frequencies you must first place the model
3152A in PLL mode. Use the following command :
PLL:LOCK ON
If no valid reference signal is applied to the trigger input, the
PLL ON LED remains off. If you feel that the 3152A should lock
and it does not, do the following:
Check that trigger level is adjusted correctly. You may change
trigger level settings using the TRIG:LEV command. The
default trigger level setting is 1.6 V.
Check that the 3152A frequency setting permits lock in the
required range. Two graphs, one for fixed mode and the other
for user mode are given in Appendix A, showing the lock range
relationship between the reference and the internal frequency
settings.
FREQuency:EXTernal?
queries the external frequency in Hz. 0.000e0 reading indicates
that no valid signal is available at the trigger input.
Using the Phase
Modulation Input
The phase modulation function operates in conjunction with the
front-panel PLL function. The PM Input accepts signals that
phase modulate the main output frequency after it has locked to
an external reference. Note that this input is active at all times
and unless you intend to use this function, do not connect any
cables to this input during normal operation of the Model 3152A.
When the Model 3152A is placed in PLL mode, the phase of the
main output signal may be shifted from the reference phase
using the phase modulation input. Although not very accurate,
the phase modulation input provides a way of phase offsetting
the main output above and below 360
o
.
The PM IN is sensitive to voltage levels. Applying 1 V to this
input generates a phase offset of 20
o
. Likewise, applying -1 V
to this input generates a phase offset of -20
o
. You may apply
20V to this input and generate a phase offset of 400
o
. The
applied frequency range is dc to 10KHz, depending on the lock
frequency and the number of waveform samples.