Scenario 2 - Proving the Link
Shift Turnover Notes
Section titled “Shift Turnover Notes”Date: Tuesday, 1345 Local (Galway runs UTC in March) Station: GW-01 Galway, Ireland - NATS Europe Operator on Duty: You Site Lead: Charlie Brooks (on-site, front office, on the phone to Rotterdam)
Yesterday counted as first light. It does not count as acceptance. Rotterdam wants a number on a signed card before they schedule us for real tasking, and the number has to be predicted before it is measured or it is not a test, it is a guess that happened to work.
Survey figures are on the Link Analysis console. Read the ones you can check off the rack first. Do the arithmetic before AOS. The pass is seven minutes and the part you can measure on is about three.
- Charlie (text, 1344)
GW-01 remains in commissioning. Yesterday’s contacts proved the chain can decode a MERIDIAN downlink; today’s test card GW-01-ATP-002 proves the station performs to the figure on the contract, and shows the measured curve follows the geometry.
Current Operations
Section titled “Current Operations”| Satellite | Type | Owner/Ops | Status at Turnover |
|---|---|---|---|
| MERIDIAN-SAR-1 | LEO SAR imager (sun-sync) | MERIDIAN Constellation Operations (Rotterdam) | Healthy; acceptance pass this shift |
| MERIDIAN-SAR-2 | LEO SAR imager (sun-sync, offset plane) | MERIDIAN Constellation Operations (Rotterdam) | Healthy; not on the card, available for a regression run |
Acceptance Test Card GW-01-ATP-002
Section titled “Acceptance Test Card GW-01-ATP-002”Test: MERIDIAN-SAR-1 imagery downlink, C/N at maximum elevation Method: Predict from link budget; measure on the live receiver at three points on the pass; accept if the culmination measurement clears the demodulator threshold with margin and the shoulder readings follow the geometry.
Site Survey Inputs (as loaded on the Link Analysis console)
Section titled “Site Survey Inputs (as loaded on the Link Analysis console)”| Parameter | Value | Source | Verifiable on the rack? |
|---|---|---|---|
| Satellite EIRP | 31.3 dBm | MERIDIAN payload data sheet | No |
| Slant range at max elevation | 761 km | Pass geometry, 28° culmination | Pass Schedule tab |
| Free-space path loss at 11,686 MHz | 171.4 dB | From the range above | Arithmetic |
| GW-01 receive antenna gain | 50.4 dBi | 4 m Ku, measured at the LNA flange (feed loss included) | No |
| LNB gain | 65 dB | Survey; read it on RX Analysis | Yes |
| System noise temperature | 125 K | LNB 60 K plus the antenna: sky, atmosphere, spillover and feed, about 65 K at 28° | No (understand it) |
| Occupied bandwidth | 36 MHz | QPSK 3/4 imagery carrier | Yes (modem) |
| Implementation loss | 1 dB | Pointing, polarization, modem | No |
Reference: C/N = EIRP + Grx − FSPL − Limpl − 10 log10(k · Tsys · B), with k = −228.6 dBW/K/Hz. Mind the EIRP unit; the survey quotes dBm.
Path loss scales with range squared: 20 log10(range ratio). At the 5° mask the slant range is 2,270 km, three times the culmination range, and FSPL is 180.9 dB, 9.5 dB worse. That is the whole reason the measurement window is the middle of the pass.
Pass Criteria
Section titled “Pass Criteria”| Check | Criterion |
|---|---|
| Predicted C/N | Within 1.0 dB of the design figure on the card (~11.4 dB) |
| Demodulator threshold | 4.2 dB C/N (QPSK 3/4: Es/N0 5.0 dB in the 30 Msps carrier) |
| Required margin at acceptance | 4.0 dB over threshold (C/N 8.2 dB), measured live at culmination |
| Shoulder readings | C/N at ~15° elevation on the rising and setting legs, about 7 dB each; the two must agree |
| Measurement point | On boresight under program-track, 14:06:45, 28°, 761 km |
Pass Plan (from the scheduler, 5° mask, epoch 13:45:00 UTC)
Section titled “Pass Plan (from the scheduler, 5° mask, epoch 13:45:00 UTC)”| Contact | AOS | Rise azimuth | Max Elevation | LOS |
|---|---|---|---|---|
| MERIDIAN-SAR-1 | 14:03:10 | 000° | 28° at 14:06:45, 761 km | 14:10:18 |
| MERIDIAN-SAR-2 | 14:18:42 | 130° | 25° at 14:22:10, 828 km | 14:25:40 |
Expected settled C/N on SAR-1 through the chain: 5.5 dB at 10°, about 7 dB at 15°, 8 dB at 18°, 10.9 dB at culmination, and the same numbers in reverse on the way down.
SAR-2 is not part of the test card. Run it as a regression: a second bird on a second geometry against the same model should come in around 10 dB at its 25° culmination.
Link Parameters
Section titled “Link Parameters”LNB is high-side injection: IF = LO − RF (13,100 MHz LO).
| Signal | RF (MHz) | IF (MHz) | Format |
|---|---|---|---|
| SAR-1 imagery downlink | 11,686 | 1,414 | QPSK 3/4, 36 MHz |
| SAR-1 telemetry beacon | 11,711 | 1,389 | CW |
| SAR-2 imagery downlink | 11,730 | 1,370 | QPSK 3/4, 36 MHz |
| SAR-2 telemetry beacon | 11,703 | 1,397 | CW |
GW-01 Equipment Status
Section titled “GW-01 Equipment Status”| Equipment | Status | Notes |
|---|---|---|
| 4 m Ku tracker | Powered, manual, parked az 5° / el 3° | Program-track available; ephemeris current |
| LNB | 13,100 MHz LO, gain 65 dB, reference locked | 60 K noise temperature, thermally stable |
| GPSDO | Locked, 9 satellites | Disciplined |
| RX modem 1 | 1,414 MHz / 36 MHz / QPSK 3/4 | Pre-tuned for SAR-1 imagery |
| BUC / HPA | Muted / output disabled | Receive-only card. Confirm both on TX Chain and leave them. |
| Link Analysis console | Worksheet blank, test card loaded | Predicted panel reads NO SOLUTION until you compute |
Acceptance Checklist
Section titled “Acceptance Checklist”Before AOS (13:45 – 14:03)
Section titled “Before AOS (13:45 – 14:03)”- TX Chain: HPA output disabled, BUC muted
- GPS Timing: GPSDO locked; RX Analysis: LNB thermally stable, gain 65 dB
- Link Analysis: survey inputs entered, C/N computed, predicted panel agrees with the card
- Path loss at the mask worked out (180.9 dB) and the window understood
- Pass Schedule: culmination time and elevation confirmed
- Antenna: program-track enabled, target MERIDIAN-SAR-1, before 14:03
During the Pass (14:03 – 14:10)
Section titled “During the Pass (14:03 – 14:10)”- SAR-1 beacon visible on RX analysis
- Rising leg: modem locked, C/N read near 15° (about 7 dB)
- Culmination: live margin at or above 4.0 dB, Commit Link pressed
- Setting leg: C/N read near 15° on the way down; compare with the rising leg
After LOS
Section titled “After LOS”- Measurement section of the card: prediction, measurement, margin, both shoulder readings
- RX modem 1 retuned to 1,370 MHz for the SAR-2 regression run
- Verdict signed: measured versus predicted, and why both are required
End of Briefing
Section titled “End of Briefing”A measurement that matches a prediction is evidence the station is performing as designed. A good measurement from a broken model is luck, and Rotterdam does not schedule tasking on luck.
Two shoulder readings that agree prove the curve. One culmination reading that matches the model proves the station. Charlie will countersign whatever you put on the card. Make it a number you can defend.
Good luck.