Racal Instruments 3152, User Manual

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Using The Instrument 3-34
PHASe2:LOCK?
queries the PLL’s state. It returns a “0” (OFF) or “1” (ON).
PHASe2:ADJust?
queries the PLL offset. It returns a value in degrees.
PHASe2:FINE?
queries the PLL’s fine offset. It returns a value in degrees.
Using the Frequency
Counter
In PLL mode, the Model 3152 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 500 Hz to 10 MHz with 4 digit
resolution.
To measure external frequencies you must first place the model
3152 in PLL mode. Use the following command :
PHASe2:LOCK ON
If no valid reference signal is applied to the trigger input, the PLL
ON LED remains off. If you feel that the 3152 should lock and it
does not, do the following:
1. 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.
2. Check that the 3152 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. Returns 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 3152.
When the Model 3152 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
E
.