Data Collection Effort Objectives Time of Transmission (TOT) monitors Time of Arrival (TOA) monitors Pulse Analysis Measurements re UTC, & sign of delay from transmitter to base of antenna Dr. Ben Peterson, Peterson Integrated Geopositioning & LT Kevin Carroll, USCG Loran Support Unit Outline

Data Collection – Objectives & Plans Bound temporal ASF (& ECD) variations –Past USCG data shows largest variations in NE CONUS – area of initial concentration –Determine if real time corrections needed –Determine model to separate correlated & uncorrelated portions of ASF prediction errors Bound spatial ASF (& ECD) variations –Can regional ASF values be used at runways never calibrated & if so, where? Use Plumbrook/LSU monitor data, land at airports in the region, collect brief period of stationary data (OU, FAA-TC) SatMate in TOA mode but not referenced to GPS time –Are there large spatial variations along approaches in rugged terrain? Do multiple approaches at selected airports (SE Coast of AK?)

Data Collection – Objectives & Plans II Bound TOT & ECD noise and bias in transmitter Define what is meant by synchronization to UTC and develop measurement procedures –Delay from installed transformer to base of antenna

TOT & TOA Monitor Network Secondary TOT – Operating Secondary TOT – Planned near term Master TOT – Operating TFE – Jan 03 TOA – Operating TOA – Planned near term TOA - Planned Phase 2 No current plans (SAMs & LORSTAs)

Time of Transmission (TOT) at Secondaries Discussed at LORIPP I at Stanford 7/25 Designed, developed, tested, and 1 st site (Nantucket) 3 weeks later. Carolina Beach & Baudette soon after. Plan to install at other secondaries (Gillette & Grangeville in near future) Could we get better data if: –We used daily or longer averages of GPS 1 pps vs Cesium to average out multi-path & other GPS errors and/or –We eliminated uncertainty of timing in EPA strobes by using signal from dedicated transformer (either digitized or stop input to TIC)? Interim only, removed with installation of TFE

TOT Measurement System Digital Averaging O’scope Antenna current transformers Envelope Trigger Circuitry in EPA TrueTime XLDC GPS Timing Rcvr Event Time Input Computer RS-232 Temporary at antenna base for calibration Permanent

Note: * 133 = * 166 = sec.

Nantucket TOT data 9960M 200 ns time step

Enhanced TOT Measurement System DSO or TIC Synthesizer & Counter TrueTime XLDC GPS Timing Rcvr Event Time Input Computer RS-232 Permanently install transformer Cesium TIC Trigger/Start 1 pps Enables long term averaging to mitigate GPS error Eliminates EPA circuitry uncertainty

Present TOA Monitor LOCUS LRS IIID in TOA mode TrueTime GPS Timing RF Gate Out Event Time In Computer RS 232 Discussed at LORIPP II in Portland Operating for past week in Connecticut

Sample TOA data Need to get TOTM data to back out time steps/eliminate steps Large ( ns pp) diurnal variations, could be GPS? 180 ns time step 280 ns time step

Future TOA SAM sites LOCUS LRS IIID TrueTime GPS Timing RF Gate Out Event Time In Computer RS 232 LOCUS LRS IIID NAVCEN Watchstander Splitter LOCUS LRS IIID TrueTime GPS Timing RF Gate Out Event Time In Computer RS 232 NAVCEN Watchstander Shared Receiver Separate Receiver

TOA Monitors w/ Shared Receivers - Options Option 1: Locus modifies software to allow UPDATE output to be in TOA mode, RPRT format in TD mode –Not till March 03. –UPDATE format is long message which scrolls by watchstander; Is this acceptable? –Cost is $, not LSU time. Option 2: LSU modifies control software so that receiver can be put in TOA mode –Convert TOA’s to TD’s in both strip charts and raw msg –Requires extensive testing, probably a non-starter Option 3: Leave receiver in TD mode, TOA monitor software cycles RF gate out among GRI’s tracked –RPRT message may have include lines for signals watchstander doesn’t care about but we do –Will need RS-232 MUX for dual rated PCMS sites –Occasional RF GATE message will scroll on watchstanders screen N per sample time where N = GRI’s tracked. Sample time = minutes. If message comes when watchstander sending command, both could get garbled

Calibration of TOA Monitor LOCUS LRS IIID in TOA mode TrueTime GPS Timing RF Gate Out Pre-Amp Digital O’scope Trigger Pre- Amp Digital O’scope Trigger PCI Counter 10 kHz Event Time In At each SAM In the near far field Calibrate the calibration system by comparing to transmitting antenna current, may be best method to calibrate synchronization of transmitters.

Pulse Analysis System Pentium PC w/ICS-650 (12 bit) Prototype developed & tested at Baudette 5 SEPT, further testing & Boise City OCT Logged TOT, ECD, and Amplitude of each pulse Logged no raw RF Baudette, Logged raw Boise City (~40GB) Processed 2/3 of the Baudette (one rate only) w/800 MHz P3, 94% w/2 GHz Boise City Antenna Current Transformer

17 Hrs 10/23-24, tower iced overnight

Before Icing

After Icing (Present SSX has no closed loop control of ECD, new one will and new controllers on old SSXs will as well. I think.)

Mean TOT & ECD as function of pulse number (Present Signal Spec defines sync to UTC by 1 st pulse of GRI A, needs changing. TFE is being changed to control average of all 16 pulses)

Example of TOT offset due to Cross Rate (Red: Period = * 96.1ms = * 89.7ms = sec, period for Searchlight = (99.4ms x 96.1 ms)/(99.4ms ms) = 2.89 sec)

From TOTM Manual Issue: ‘+’ sign means signal at transformer earlier than at antenna base. If sign were wrong, Dana would be off by 806 ns, Seneca by 94 ns, etc.

Determination of delay from RF ground return at transmitter to that at antenna base Hardware Diagram for Lessay & Seneca PCI trigger Digital Oscilloscope 100 MHz & 8 bits Ch1Ch2 Transmitter Ground Return Permanently Installed Transformer near Transmitter Temporary Transformer at base of antenna

Determination of delay from RF ground return at transmitter to that at antenna base After taking into account all the cable delays –At Lessay: Signal at transmitter was 80 ns later than that at antenna base (i.e. the sign is wrong) –At Seneca: Signal at transmitter was 50 ns earlier than that at antenna base (i.e. the sign is right) But…. Different cables & transformers, how well are the various delays known?

Determination of delay from RF ground return at transmitter to that at antenna base Hardware Diagram for Boise City 9610 PCI trigger from TOTM Digital Oscilloscope 100 MHz & 8 bits Ch1Ch2 Transmitter Ground Return Permanently Installed TOTM transformer Temporary Transformer One set of antenna base, 2 nd set adjacent to TOTM transformer

Transformers adjacent, Ch1 TOTM, Ch2 Temporary, 123 sweeps (Times in usec into record, record started 35 usec before trigger from TOTM or ~10 usec prior to start of pulse)

Transformers adjacent, blowup of 30 usec point

Transformers adjacent, blowup of 35 usec point

Illustration of determination of zero crossing (Times in usec re nominal 20 usec point)

Transformers adjacent (23 Oct)

Transformers Adjacent (23 OCT)

Transformers adjacent (24 OCT)

Temporary Transformer Antenna Base (23 OCT)

Temporary Transformer Antenna Base, 24 Oct

Master TOTM Data: 8970 = -560ns, 9960 = -185 ns before, 81 ns after time step = -375 ns before, -641 ns after time step If sign were wrong and ED correct, should be in error by over 700 ns. On 9 Oct we (DCN & I) measured 8970X as 280 ns early, TOTM data had Dana 574 ns early, i.e 8970X ED was 200 ns large, assuming this was still true on 2 weeks later, data agrees very well

Master TOTM Data: 8970 = -560ns, 9960 = -185 ns before, 81 ns after time step = -375 ns before, -641 ns after time step If sign were wrong and ED correct, should be in error by over 700 ns.

Summary – RF ground return delay Measurements at Lessay & Seneca not consistent Measurements at Boise City not conclusive –Signals virtually simultaneous, slightly in direction of TOTM manual, but not at predicted magnitude Seneca & Dana TOA data strongly suggest the sign is correct Considering visit to Dana My opinion: Ability to steer local time scale (<10ns) far exceeds ability to measure TOT relative to that time scale –Cost to improve time transfer to 1ns level not warranted unless data is used as input to UTC time scale –In addition, medium frequency variations (1-20 sec) exist that are not averaged out in user equipment but cannot be eliminated in control loop.

Summary TOT monitors developed –Baudette, Nantucket & Carolina Beach operating –Grangeville & Gillette next in line Prototype TOA monitor developed & being tested –Coordinate with LSU & NAVCEN on development of version for SAM sites Getting good data from pulse analysis system My opinion: Very limited number of absolute time or cross chain navigation users (maybe 0), larger number of frequency users, large master time steps jeopardize Loran’s ability to meet Stratum 1 requirements.

A final question/live hand grenade Is the Nome station expected to support NPA’s at Nome Airport?

TOT & TOA Monitor Network Secondary TOT – Operating Secondary TOT – Planned near term Master TOT – Operating TFE – Jan 03 TOA – Operating TOA – Planned near term TOA - Planned Phase 2 No current plans (SAMs & LORSTAs)

Equipment Requirements