Jackson Labs FireFox, Руководство пользователя

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FireFox Synthesizer User Manual
50 © 2006 Jackson-Labs
AS, 3D, 2D - Position fixes. The unit is receiving 3D or 2D position fixes when in Auto Survey
mode. Ten thousand readings are required to finish Auto Survey mode.
OK - Position hold mode with locked OCXO. The unit has locked the OCXO to UTC, and sufficient
satellites are being received to maintain lock.
3.6 Performance FAQs
The following FAQs describe the performance of the FireFox Signal Generators, and it’s features.
3.6.1 How does the FireFox Synthesizer offer such wide
bandwidth?
The FireFox synthesizers' internal circuitry divides the output bandwidth into four bands, with each
band optimized to reduce noise, spurs, and to offer the best linearity possible. The frequency bands
are: DC (0.00001Hz) to 30MHz, 30MHz to 390MHz, 390MHz to 770MHz, and 770MHz to
1.64GHz. These bands are switched seamlessly in the background. A Direct Digital Synthesizer
(DDS) with a 10-bit DAC and 1GHz sample rate generates the first two bands (DC to 390MHz).
Frequencies above 390MHz are generated by a very low phase noise PLL controlled VCO
phase-locked to the internal DDS.
3.6.2 How can spur performance be increased even further?
An LC-type output filter can be used to reduce out-of-band spurs. These filters can be designed with
public-domain software (see for example "Elsie", an easy to use filter designer available at
www.tonnesoftware.com), or these can be purchased off-the-shelf. Mini Circuits
(www.minicircuits.com) offers such filters as small inexpensive ceramic components in their LFCN
and HFCN series filters.
3.6.3 Does the FireFox need calibration?
The FireFox system never needs frequency calibration; it is constantly being calibrated by the GPS
timing signal. The FireFox RF output amplitude has been calibrated at the factory, and it is
recommended that the unit is returned to Jackson Labs once a year for amplitude calibration. The
user may also self-calibrate the FireFox units using an Agilent power meter; see the hardware FAQ.
3.6.4 There is a Frequency Estimate display in the menus. What
is this number?
The FireFox system constantly measures the internal OCXO offset to the GPS 1PPS signal. This
measurement is done in 10ns steps (100MHz sampling). The firmware then adjusts the OCXO
steering voltage (Electronic Frequency Control - EFC) to compensate for any drift between the
OCXO and UTC. The timing differences between the OCXO and the 1PPS signal are stored in
memory once per minute over a 30-minute period. The momentary difference is then compared to the
difference that was measured 30 minutes ago, and a drift is calculated from these two values. Thus an