3.2.9
Frequency Modulation
This feature is implemented by injecting a modulation signal into the output phase lock loop
circuit. The modulation input is summed with the output of the loop phase detector and
integrator; the combined signal drives the FM (fine tuning) coil of the YIG oscillator. Because
of the modulation input, the input to the FM coil varies; the YIG output frequency tracks these
variations.
3.2.10
Amplitude Modulation
Amplitude modulation is accomplished by adding a modulation input to the level control loop.
The AM input is combined with the leveling reference generated by the CPU and DAC, in such
a way that the amplitude of the modulating signal tracks any changes in level (this insures that
AM depth remains constant for different levels). The level control output to the leveler is
modulated by the AM input waveform, and the RF output becomes amplitude modulated.
This modulation method is not used in instruments with Option 27 (see Appendix A).
3.2.11
Pulse Modulation
Pulse modulation is essentially a means of shutting off the output signal for short periods. The
modulation OFF pulses are applied to PIN diode switches within the RF module. During the
OFF intervals, the particular RF path which is normally activated for the present output
frequency is temporarily shut down. That is, during the ON periods one output path is open, and
during the OFF periods no output path is open.
The very fast rising and falling edges of the modulating pulses are produced by pulse driver
circuits, in response to a modulation waveform. The modulation waveform can be generated
within the instrument, or it can be supplied by an external source. The internal modulation
source is a pulse generator with variable pulse rate, width, and delay. The instrument timebase
is used as a reference by the generator, so all rates and intervals are highly accurate. For the
purpose of synchronizing auxiliary instruments, a TTL level modulation waveform output is
available, whether the modulation source is internal or external.
Figure 3-10. Frequency modulation
Theory of Operation
Manual No. 120AM00250, Rev C, September 1998
3-17
Содержание GT 9000
Страница 12: ...Series GT 9000 Microwave Synthesizers x Manual No 120AM00250 Rev C September 1998 ...
Страница 14: ...Series GT 9000 Microwave Synthesizers xii Manual No 120AM00250 Rev C September 1998 ...
Страница 18: ...Series GT 9000 Microwave Synthesizers xvi Manual No 120AM00250 Rev C September 1998 ...
Страница 20: ...Series GT 9000 Microwave Synthesizers xviii Manual No 120AM00250 Rev C September 1998 ...
Страница 94: ...Model GT 9000 Microwave Synthesizer 3 36 Manual No 120AM00250 Rev C September 1998 ...
Страница 122: ...Model GT 9000 Microwave Synthesizer 4 28 Manual No 120AM00250 Rev C September 1998 ...
Страница 129: ...6 Check the level control circuit see Section 5 3 7 Maintenance Manual No 120AM00250 Rev C September 1998 5 3 ...
Страница 142: ...Model GT 9000 Microwave Synthesizer 5 16 Manual No 120AM00250 Rev C September 1998 ...
Страница 198: ...Model GT 9000 Microwave Synthesizer 6 56 Manual No 120AM00250 Rev C September 1998 ...
Страница 206: ...Model GT 9000 Microwave Synthesizers 7 2 Manual No 120AM00250 Rev C September 1998 ...
Страница 232: ...Model GT 9000 Microwave Synthesizer A 26 Manual No 120AM00250 Rev C September 1998 ...
Страница 238: ...Model GT 9000 Microwave Synthesizer Index 6 Manual No 120AM00250 Rev C September 1998 ...