Jackson Labs FireFox, User Manual

Page: 15 / 68

© 2006 Jackson-Labs 9
FireFox Synthesizer User Manual
1.4.7 Setting up the DDS
Enter the menu SETUP->DDS to control the internal settings of the FireFox Signal Generator RF
DDS (Digital Direct Signal Generator).
1.4.7.1 Setting the Phase Offset
Enter the SETUP->DDS->PHASE OFFSET menu item to control the output Frequencies’ phase in
relation to the rear panel 10MHz time base output. The user can select the phase in small increments
from -180 Degrees to +180 Degrees.
1.4.7.2 Mixer ON/OFF
The FireFox Signal Generator has a general-purpose, non-dedicated 2GHz Bandwidth mixer built-in,
accessible through the front panel BNC connectors.
This mixer can be turned ON or OFF via the
SETUP->DDS->MIXER menu.
Turning off the mixer may help prevent some spurs, and may be usefull when debugging IF and AGC
circuitry etc.
1.4.7.3 FRACT ON/OFF
The menu item SETUP->DDS->FRACT ON/OFF determines the mode of the FireFox Signal
Generator Fractional-N DDS to be used or to be disabled. This setting determines the FireFox Signal
Generator resolution, and also affects the output phase noise and frequency drift. Select FRACT ON
to set the DDS to 48-bit Frequency mode, or FRACT OFF to turn off the Fractional-N mode, and set
the unit to 32-bit Frequency mode.
See Section
3.6.6 for an in-depth discussion of the Fractional-N operating mode.
1.4.7.4 Noise/Spur Optimization
The menu item SETUP->DDS->NOISE/SPUR OPT allows the internal FireFox PLLs’ to be setup
for either best-noise performance (Spur optimization turned to OFF) or best-spur performance (Spur
optimization turned to ON). This setting will affect the PLL charge currents of the internal PLLs’ and
place these either in the best operating mode for Phase Noise performance, or for least-Spur
performance.
Set this item to OFF for typical operations that require low phase-noise signals.
1.4.8 Setting up the Output
The following settings affect the FireFox maximum frequency that can be generated, as well as the
analog front panel RF Output power.
1.4.8.1 Frequency Limit
In the SETUP->OUTPUT->FREQ LIMIT menu the user may limit the maximum possible frequency
that can be set via the front panel keys in the frequency setting menu. This setting will also affect
sweep modes, and memory recall modes.