
Considerations with Enhancing the Tuning Range.
• The system is instructed to use a Voltage Tuning Range that exceeds
the calibrated Tune Port input of the VCO. Typically a Voltage Tune
Range of 5 to 10 volts is entered at the Instrument Parameter display
to artificially increase the PTR by 5 to 10 times. This increases the Drift
Tracking Range allowed which is 20% of the PTR enabling the System
to use the total VCO Tuning Range available. For example an HP
8663A with 10 kHz DC FM and 1 volt peak deviation would normally
result in a PTR of 10 kHz and a Drift Tracking Range of 2 kHz. Any
drift greater than 2 kHz the system would break lock because the HP
8663A was restricted to ± .2 volts at the tune port and could not track
the drift. With Enhanced Tuning applied the system would think that
the same HP 8663A would have a PTR of 10 x the peak deviation of
10 kHz, or 100 kHz. This allows a Drift Tracking Range of 20 kHz and
a Capture Range of 10 kHz. Even though the Enhance Drift Tracking
Range exceeds the peak deviation of the HP 8663A the system will
track the sources until the Voltage Tune Range exceeds 20% of the
Voltage Tuning Range or the VCO fails to compensate for the drift
due to its capabilities, (non-linearity).
NOTE
The System will apply the full Voltage Tuning Range when
the phase lock is lost. The 1.6 Hz Search Oscillator internal
to the HP 11848A Interface is enabled to swing the Voltage
Tune Port ± the Voltage Tuning Range this allows the
system to re-lock the loop when possible under normal
tuning.
Instr. Params: $N w/PLL 2-29
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