1 loran timing ila – 36 th convention and technical symposium orlando, fl., oct 16-17 2007 arthur...
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1
Loran Timing
ILA – 36th Convention and Technical SymposiumOrlando, Fl., Oct 16-17 2007
Arthur HelwigGerard Offermans
Christian Farrow
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Outline
•Timing and Frequency use•Developing High-end Loran-C timing equipment (recap)
•Developing Low-end Loran-C timing equipment–Low-cost oscillator characterizaton–Received signal–Combining the two
•Conclusions
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Outline
TimingFrequency
Time andFrequency
Receiver outputs:• 10 MHz• 2.048 MHz• 1.544 MHz
Necessary input:• eLoran/Loran-C signal
Receiver outputs:Frequency outputs, plus:• 1 PPS (aligned to UTC)• 10 PPS• 100 PPS• Serial output for
Time of Day message
Necessary inputs:• eLoran signal• Data channel for UTC
information
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MTIE / TDEV
Relevant measurements:• MTIE
–Maximum Time Interval Error (MTIE): The maximum peak-to-peak delay variation of a given timing signal with respect to an ideal timing signal within an observation time τnτ for all observation times of that length within the measurement period (Τ).
• TDEV–Time Deviation (TDEV or σx(τ)): A measure of
the expected time variation of a signal as a function of integration time. TDEV can also provide information about the spectral content of the phase (or time) noise of a signal. TDEV is in units of time.
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ETSI – EN 300 462- 3 - 1
ETSI EN 300 462-3-1 V1.1.1 (1998-05)
Transmission and Multiplexing (TM);Generic requirements for synchronization networks;Part 3-1: The control of jitter and wander withinsynchronization networks
• 864 ns / day• ASF fluctuations
not a problem
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Loradd UTC series
• All functionalities of a normal LORADD receiver• Ovenized crystal for improved stability and hold-over (SRS SC10)• 10 MHz, 2.048 MHz and 1.544 MHz outputs• 1 PPS (Loran-C derived) output• 1 PPS (GPS derived) output• Loran-C Timing Source Station selectable
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Test results - MTIE
ETSI PRC Mask
Loradd UTC performance10 ns
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Test results - TDEV
ETSI PRC Mask
Loradd UTC performance
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Low-cost
•Market demand for low-cost frequency-only receiver
•Frequency lock to a single Loran station
•No hold-over required
•Low-cost oscillator means shorter integration of received Loran signals
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•Loradd-F•Low-cost VCO
•No GPS•10 MHz output via SMA
Loradd-F
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Low-cost oscillator characterization
• Crystal oscillator frequency varies
• Graph displays frequency vs time
• Receiver operating at room temperature
• After warming up for several days
• Most likely still due to temperature variations
Free-running VCO
Time (s)
Fre
quen
cy e
rror
(ns
/s)
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200 s
4e-10
Low-cost oscillator characterization
Time interval: 200sFrequency error: 4e-10Phase error (over 200 s): 40 ns
MTIE mask: 25 ns
When left uncorrected, MTIEmask is broken at this point.
Free-running VCO
Time (s)
Fre
quen
cy e
rror
(ns
/s)
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Received signal characterization
Rugby (6731Y)
5-second independent measurements
6731Y std=10.44 ns
TOA of Rugby (6731Y) @ Reeuwijk (408 km)
Time (s)
Mea
sure
d T
OA
(ns
)
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Received signal characterization
Rugby (6731Y)
5-second independent measurements with 3-point moving median filter
6731Y std=8.18 ns
Transmitters are currently broadcasting in
a 10ns “grid”200 s
TOA of Rugby (6731Y) @ Reeuwijk (408 km)
Time (s)
Mea
sure
d T
OA
(ns
)
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Combining the two
Low-quality VCO Loran TOA
MTIE MTIE
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Combining the two
Low-quality VCO Simulated Loran TOA (σ=3.5 ns)No timing steps
MTIE MTIE
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Conclusions
•Loradd UTC with high quality VCO fully meets MTIE specification
•Loradd-F with low-quality VCO does not yet meet MTE spec at 25<τ<110 s–Temperature controlled VCO–Higher grade VCO
•Timing steps in transmitter need to be investigated. Elimination will result in reduced cost receivers.