Racal Instruments 3152, User Manual

Page: 58 / 123

Using The Instrument 3-33
Phase offset resolution depends on the number of waveform
samples. For instance, if you have 1000 waveform samples,
there is no problem with adjusting the phase offset in 1
EE
increments (360
EE
/ 1000 < 1). As another example, if you have
only 10 waveform samples, the best phase offset increments
are only 36
EE
(360
EE
/ 10 = 36
EE
).
NOTE
There is a special fine adjustment for phase offset with a 36
E
range. This adjustment is useful in places where a 36
E
gap is too
wide. The fine phase adjustment improves phase offset settings to
0.01
E
and can be used in conjunction with the coarse phase offset
adjustment at any phase offset setting point.
PLL Commands
In PLL mode, the Model 3152 can be used as a slave only. Use the
following commands to program the Model 3152 to lock to an
external reference.
PHASe2:LOCK ON
This command places the Model 3152 in PLL mode. 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,
check the following:
1. Make sure that trigger level is adjusted correctly
2. Make sure 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
.
.
PHASe2:ADJust <value>
applies a phase offset between the reference signal and the main
output. The default value is 0
E
. Phase offsets can be adjusted
between -180
E
and +180
E
. Best resolution for this parameter is 1
E
,
degrading to 36
E
at 10 point waveform samples.
PHASe2:FINE <value>
applies a fine adjustment to the absolute setting of the PHAS[2]:ADJ
command. The default value is 0
E
. Fine phase adjustment is
usable between -36
E
and +36
E
.
As an example of the use of this command, we’ll take a 100 sample
waveform. The best phase offset resolution for this waveform is
3.6
E
(360
E
/ 100 points). If you need to set an offset of 50
E
, the
Model 3152 will accept this value, but will not be able to set this
offset correctly. Since the resolution is 3.6
E
, the output will offset
by 50.4
E
. You can now correct the phase to exactly 50
E
by using
the PHAS:FINE -0.4 command.