Verifying EIRP (Effective Isotropic Radiated Power) and uplink performance is how you turn “it should work” into “it is working.” In satellite ground operations, uplink issues can look like random packet loss, unstable lock, poor modem performance, or intermittent command failures—but the root cause is often a measurable mismatch in power, pointing, frequency, polarization, or hardware health. This guide outlines practical methods to validate uplink performance and the logs you should capture so results are repeatable and auditable.
Table of contents
- What EIRP Means in Uplink Verification
- What to Verify Beyond EIRP
- Pre-Test Checklist Before You Transmit
- Methods to Verify EIRP and Uplink Performance
- Using Satellite Feedback: Eb/No and Modem Metrics
- Common Logs to Capture and How to Structure Them
- Validation Tests: Step-Ups, Step-Downs, and Linearity
- Troubleshooting Signatures and What They Usually Mean
- Compliance and Safety Considerations
- EIRP and Uplink Verification FAQ
- Glossary
What EIRP Means in Uplink Verification
EIRP is the effective radiated power of your uplink in the direction of the satellite. It combines your transmitter output power with antenna gain (minus losses like waveguide, coax, filters, and pointing loss). In practice, EIRP is the number that determines whether the satellite receives enough signal quality to demodulate your uplink.
Because uplink power can be high and downlink signals are often weak, verifying EIRP is also part of interference prevention. You want enough margin to meet service requirements—without transmitting more power than needed or exceeding licensed limits.
What to Verify Beyond EIRP
EIRP alone is not “uplink performance.” A healthy uplink includes:
Frequency accuracy: correct center frequency and stability (including Doppler planning for LEO).
Polarization alignment: correct polarization and skew (especially important at Ku/Ka).
Pointing accuracy: antenna boresight aligned with the satellite and tracking stable.
Modem health: clean modulation, correct symbol rate, coding, roll-off, and proper framing.
Linearity and spectral cleanliness: no compression, regrowth, or spurious emissions that reduce performance or violate masks.
Pre-Test Checklist Before You Transmit
Before you key up, ensure you have a controlled, repeatable setup:
Confirm authorization: frequency assignment, power limits, and any coordination constraints for the test window.
Verify RF path configuration: correct filters, switch states, waveguide routing, attenuators, and redundancy selection.
Validate calibration data: up-to-date antenna gain tables, loss budgets, and HPA output calibration (forward/reflected power sensors).
Check safety interlocks: E-stop, waveguide pressure (if applicable), RF hazard signage, and operational approvals.
Establish baselines: reference levels on spectrum analyzer, modem idle metrics, and known-good test carriers if available.
Methods to Verify EIRP and Uplink Performance
1) Measure conducted power at the transmitter chain
The most direct method is to measure power in the RF chain with calibrated sensors or couplers—typically at the HPA output or after major components. This confirms what you are actually putting into the antenna feed (or waveguide) and helps catch misconfigurations and hardware drift.
2) Convert conducted power to EIRP using a loss and gain budget
EIRP is calculated by combining measured conducted power with known antenna gain and measured/estimated losses. Losses include waveguide/coax, filters, diplexers, OMTs, switches, and any intentional attenuation. Pointing loss and polarization mismatch can be treated as additional losses when precision matters.
3) Validate spectral shape and cleanliness
A spectrum analyzer view is essential. It confirms you are on-frequency, within bandwidth, and not generating excessive shoulders or spurs. If the HPA is near compression, you may see spectral regrowth and degraded demod performance even if EIRP looks “high enough.”
4) Use an on-satellite measurement or hub feedback when available
Many networks provide feedback such as received carrier level, Eb/No, C/N, or “uplink quality” metrics. This is powerful because it measures what the satellite (or downstream demod) actually sees. You can correlate a controlled uplink power step with measured received metrics to validate end-to-end performance.
5) Use loopback or test transponders (when permitted)
In some systems, you can use a loopback path to measure the uplink indirectly via a returned downlink. When available, this enables repeatable tests without relying on live customer traffic. Always ensure loopback use is authorized and won’t interfere with operational services.
Using Satellite Feedback: Eb/No and Modem Metrics
Modem and demod metrics are often the fastest way to confirm “uplink is healthy”:
Eb/No (or Es/No): correlates with demod robustness; watch how it responds to controlled power steps.
Packet error rate / BER: confirms real performance, not just RF level.
Lock stability: frequent unlocks can indicate marginal power, frequency instability, interference, or pointing issues.
ACM state changes: if adaptive coding/modulation is active, note which MODCOD is chosen at each power level.
The goal is correlation: a known change in transmit power should produce a predictable change in received metrics. If the response is weak, inconsistent, or nonlinear, suspect compression, mispointing, polarization error, or a measurement/calibration problem.
Common Logs to Capture and How to Structure Them
Good logging makes uplink verification repeatable, reviewable, and defensible. Capture:
RF chain configuration log: switch states, filter paths, redundancy selection, attenuator settings, waveguide routing, and firmware versions.
HPA/SSPA telemetry: forward/reflected power, temperature, current draw, alarms, gain state, and any ALC/ATC settings.
Antenna and pointing telemetry: az/el, track mode, pointing model version, error terms, and weather (wind can matter).
Frequency plan: center frequency, symbol rate, roll-off, modulation/coding, polarization, and occupied bandwidth.
Spectrum snapshots: before/after key-up, during steady-state, and at each power step (include RBW/VBW/span settings).
Receiver/demod metrics: Eb/No, C/N, lock state, BER/PER, ACM/MODCOD, and alarms with timestamps.
Event timeline: exact timestamps for each action (power changes, pointing tweaks, configuration changes) so correlations are unambiguous.
Use consistent time sources (NTP/PTP where applicable) so logs from different systems line up without guesswork.
Validation Tests: Step-Ups, Step-Downs, and Linearity
Controlled stepping is one of the most useful verification methods:
Power step test: increase uplink power in small increments and record conducted power + satellite feedback metrics at each step. The relationship should
be predictable and monotonic.
Step-down / fade simulation: reduce power to find the threshold where errors begin, then restore. This helps quantify operational margin.
Linearity check: watch for the point where additional conducted power stops producing expected Eb/No improvement—often a sign of compression or regrowth.
Pointing sensitivity check: make small, controlled pointing offsets (when permitted) to confirm expected loss behavior and validate pointing models.
These tests are most valuable when done during quiet RF conditions and stable weather, so you’re measuring your system—not the environment.
Troubleshooting Signatures and What They Usually Mean
High conducted power but poor satellite Eb/No: suspect pointing loss, polarization mismatch, wrong frequency, incorrect waveguide path, or a bad gain/loss model.
Eb/No improves, but BER stays high: suspect modem misconfiguration, interference, or spectral regrowth from compression.
Intermittent lock drops: suspect tracking instability, frequency drift, intermittent RF chain faults, or interference bursts.
Nonlinear response to power steps: suspect HPA compression, ALC behavior, or incorrect power sensor calibration.
Unexpected spurs/shoulders: suspect overdrive, faulty filtering, oscillation, or damaged RF components.
Compliance and Safety Considerations
Uplink verification must respect licensing and coordination limits. Never exceed authorized EIRP, bandwidth, or emission constraints “just for testing.” Use test carriers and procedures that are approved for the band and satellite.
Also treat RF safety seriously: high-power uplinks can create hazardous exposure zones near antennas and waveguides. Ensure interlocks, signage, and site procedures are followed, and stop immediately if safety alarms trigger.
EIRP and Uplink Verification FAQ
What’s the difference between conducted power and EIRP?
Conducted power is what your transmitter produces at a point in the RF chain (often measured near the HPA output). EIRP includes antenna gain and subtracts losses, representing the effective power radiated toward the satellite.
What’s the most reliable way to verify EIRP?
The strongest approach is combining calibrated conducted power measurements with a validated gain/loss budget, then confirming end-to-end behavior using satellite or hub feedback (Eb/No, BER/PER) during controlled power steps.
Why can increasing power make performance worse?
If the HPA enters compression, the signal can distort and cause spectral regrowth, which reduces demod performance and can violate emission limits—even though the measured power is higher.
What logs matter most for post-incident analysis?
A timestamped event timeline plus HPA telemetry, antenna pointing/tracking logs, spectrum analyzer captures, and receiver/demod metrics are usually the fastest path to determining whether the issue was power, pointing, frequency, interference, or configuration drift.
Glossary
EIRP: Effective Isotropic Radiated Power—conducted transmit power plus antenna gain minus RF path losses.
HPA/SSPA: High Power Amplifier / Solid State Power Amplifier—equipment that boosts uplink power before the antenna.
Forward/Reflected power: Measurements indicating transmitted power and power reflected due to mismatch (VSWR).
Eb/No (Es/No): Energy per bit (or symbol) to noise density—key indicator of demodulation margin.
BER/PER: Bit Error Rate / Packet Error Rate—measures of actual data integrity.
Compression: Nonlinear amplifier region where output no longer increases linearly with input, causing distortion.
Spectral regrowth: Unwanted widening of a signal’s spectrum due to nonlinearity.
ALC: Automatic Level Control—control loop that regulates output level and can affect measurement behavior.
Pointing loss: Signal degradation due to antenna misalignment with the satellite.
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