Table of Contents
Advertisement
SECTION 3
Operation
3.513
Synchronous
Operation
Multiple Model 3940s can be connected together syn-
chronously to form a multiphase oscillator. The phase re-
lationship between the oscillators can be accurately de-
fined by using @ SYNC.
With the units turned off, connect the optional Model
3949 Synchronous Cable to the PHASE SYNC I/O con-
nector on the rear panel of each unit. The Model 3940
with the connector labelled "MASTER" is the master unit
and transmits clock and phase sync pulses to the slave
unit. The Model 3940 with the connector labelled
"SLAVE" is the slave unit that receives clock and phase
sync pulses transmitted from the master unit. Note that
slave unit I$ SYNC key will be inoperative, and the slave
unit will not respond to the GPIB "SYN" command.
After connecting the units and setting up waveforms and
frequencies, press the $ SYNC key on the master unit to
synchronize phases. You can then set the phases for the
units independently, and accurate phase relationships
between waveforms from the two instruments will be
maintained. The $ SYNC phase relationships for external
synchronous operation are similar to those discussed
previously for main synthesizer and the sub synthesizer
phases (see paragraph 3.5.12).
3.514
Frequency
Sweep Operation
The Model 3940 can be set up to generate frequency
sweeps over a variety of ranges. The following para-
graphs discuss the various aspects of programming fre-
quency sweeps. Figure 3-18 shows sweep waveforms,
and Figure 3-19 details sweep operation.
Setting the Sweep Range
You can set the sweep range in one of two ways: (1) by
setting the start and stop frequencies, or (2) by setting the
center and span frequencies. The actual sweep is gener-
ated from the start frequency to the stop frequency, and
the sweep direction is determined by the relative values
of the start and stop frequencies. If the start frequency is
lower than the stop frequency, an ascending-frequency
sweep will be generated. If the start frequency is higher
than the stop frequency, a descending-frequency sweep
will be generated.
3-34
If you specify the center and span frequencies to set the
sweep range, the Model 3940 will automatically convert
them into start and stop frequencies. See the specifica-
tions in Appendix B for more details on the sweep range
and sweep width.
The Model 3940 determines the sweep range as described
below when you change a frequency parameter:
When you change the start frequency:
The stop frequency remains unchanged.
Center frequency =
(start frequency + stop frequency)/2
(Portion of value below O.lmHz is truncated.)
Span frequency = I start frequency-stop
frequency I
When you change the stop frequency:
The start frequency remains unchanged.
Center frequency =
(start frequency f stop frequency)/2
(Portion of value below O.lmHz is truncated.)
Span frequency = I start frequency - stop frequency I
When you change the center frequency:
The span frequency remains unchanged.
The relationship between the start and stop frequency
values remains the same as it was before you changed
the center frequency:
Start frequency =
(center frequency T span frequency/2)
(Portion of value below O.lmHz is truncated.)
Stop frequency =
(center frequency + span frequency/2)
Portion of value below O.lmHz is truncated.)
When you change the span frequency:
The center frequency remains unchanged.
The relationship between the start and stop frequency
values remains the same as it was before you changed
the span frequency:
Start frequency =
(center frequency T span frequency/2)
(Part smaller than O.lmHz is truncated.)
Stop frequency =
(center frequency & span frequency/2)
(Part smaller than O.lmHz is truncated.)
The start and stop frequencies always correspond to the
opposite ends of the actual sweep range. When the span
frequency is an odd number of O.lmHz units, the dis-
played center frequency will be 0.05mHz lower than the
actual center frequency value. The center frequency is the
center frequency on the linear scale, and it is not the cen-
Advertisement
Table of Contents
