EIRP Verification Methods: Evidence Capture and Logging

EIRP verification is how a ground station proves that its transmitted signal is within expected power and spectral limits. It is both an engineering task and an operational discipline: you need to confirm the uplink chain is behaving as designed, and you need records that stand up to audits, customer questions, and interference investigations. This guide explains practical EIRP verification methods, what evidence to capture, and how to build logging that is useful instead of burdensome.

Table of contents

1. What EIRP Verification Is and Why It Matters
2. What You Are Actually Verifying: The EIRP Chain
3. Common Verification Approaches and How They Differ
4. Measurement Points and Typical Instruments
5. Method 1: Conducted Power Verification at RF or IF
6. Method 2: Over-the-Air Verification with a Reference Receiver
7. Method 3: Satellite Return or Beacon-Based Confirmation
8. Method 4: Spectrum Shape and Mask Compliance Checks
9. Building a Repeatable Procedure: Calibration and Uncertainty
10. Evidence Capture: What to Record for a Credible Proof Package
11. Logging and Recordkeeping: What to Store and How to Structure It
12. Common Pitfalls and How to Avoid Them
13. Glossary: EIRP and Verification Terms

What EIRP Verification Is and Why It Matters

EIRP (Effective Isotropic Radiated Power) is the transmit power a station would appear to radiate if it used a perfect, imaginary antenna that radiates equally in all directions. In practice, EIRP represents the combined effect of transmitter power, losses in the transmit chain, and antenna gain in the direction of the satellite.

Verifying EIRP matters for three main reasons:

• Mission success: too little EIRP can cause poor link performance, slow data rates, or failed uplink commands.
• Interference risk: too much EIRP can create harmful interference and trigger complaints or regulatory action.
• Accountability: customers and regulators may require evidence that uplinks were within authorized limits.

What You Are Actually Verifying: The EIRP Chain

EIRP is not just a number on a transmitter. It is the result of a chain of components and assumptions. A practical verification approach starts by clearly defining the chain from the modulated signal to the radiated beam.

A simplified uplink chain looks like this:

• Baseband/modem output: the modulated waveform and its intended symbol rate and roll-off.
• Upconversion: frequency translation and level setting.
• Driver and HPA: amplification to the required transmit power.
• Waveguide/coax and switches: losses and routing.
• Feed and antenna: antenna gain and pointing accuracy.

When a station says “we verified EIRP,” it should be clear whether that means: conducted HPA output power, calculated EIRP using antenna gain and losses, or a true over-the-air confirmation. Good records state which it is.

Common Verification Approaches and How They Differ

There is no single best method for every station. The right approach depends on whether you need an engineering check, a compliance artifact, or proof suitable for an interference investigation. Many stations use a combination.

• Conducted power + modeled losses: fast, repeatable, good for routine checks, but depends on accurate loss and gain values.
• Over-the-air measurement: directly observes the radiated signal, stronger evidence, but requires a reference receiver setup.
• Satellite-based confirmation: leverages satellite telemetry or return carriers, useful for end-to-end validation, but not always available.
• Spectral compliance checks: confirms bandwidth and emissions behavior, important for interference control.

A practical strategy is to have one primary routine method and one “strong evidence” method used periodically or during high-risk operations.

Measurement Points and Typical Instruments

Verification depends on having defined measurement points and stable instrumentation. If measurements are taken in different places at different times, results become hard to compare.

Common measurement points include:

• IF monitor point: before upconversion, useful for confirming modulation quality and relative levels.
• RF monitor point: after upconversion, useful for confirming frequency, mask, and relative power.
• HPA output sample port: used to measure conducted output power without breaking the main path.
• Coupler near the feed: helps capture a view closer to the antenna input.

Instruments often used include spectrum analyzers, power meters, directional couplers, calibrated attenuators, and reference receivers. The key is not which brand is used, but that the setup is documented and repeatable.

Method 1: Conducted Power Verification at RF or IF

Conducted verification measures power in a cable or waveguide path, then converts that measurement into EIRP using known losses and antenna gain. This is a common routine method because it can be quick and does not depend on external receiving equipment.

A practical conducted verification workflow:

• Measure HPA output power: using a sample port or coupler and a calibrated power meter.
• Apply transmit chain losses: waveguide/coax loss, switch loss, filter loss, and any radome or feed losses if included in your model.
• Apply antenna gain: gain at the operating frequency, ideally with a documented gain curve.
• Record configuration state: frequency, modulation, bandwidth, HPA mode, and pointing state.

This method is only as good as the loss and gain values you use. If losses change due to water ingress, aging connectors, or replaced components, a calculation can look “correct” while the radiated signal is not.

Method 2: Over-the-Air Verification with a Reference Receiver

Over-the-air verification measures the signal as radiated, using a separate receiving setup. This provides strong evidence because it observes the combined effect of the full transmit chain, including pointing, polarization alignment, and environmental impacts.

Practical ways to implement a reference receiver approach:

• Local receive antenna: a small calibrated antenna positioned to observe the uplink safely at a known geometry.
• Receive chain with known calibration: stable gain, measured noise figure, and documented attenuators.
• Captured spectrum and power: consistent RBW/VBW settings and a documented measurement method.

Over-the-air measurements must be done carefully. You need to avoid saturating the receiver and you need to control reflections and multipath that can skew results. The value of this method is that it validates the real radiated behavior, not just a theoretical chain.

Method 3: Satellite Return or Beacon-Based Confirmation

In some systems, you can confirm uplink power and quality using information that comes back from the satellite or the network. This can be a return carrier, telemetry from a payload, or a known response to a commanded state change.

Satellite-based confirmation is best treated as end-to-end validation:

• Confirm expected behavior: the satellite reports nominal uplink margin, lock, or received level within expected bounds.
• Correlate with station settings: record the station transmit levels, modulation parameters, and timing.
• Use controlled test waveforms: stable carriers or known patterns make comparisons easier.

This method is powerful because it confirms the uplink as the satellite experiences it. The tradeoff is that it depends on satellite capabilities and access to the right telemetry or responses.

Method 4: Spectrum Shape and Mask Compliance Checks

Verifying EIRP is not only about total power. Many operational problems are caused by spectral issues: excessive out-of-band emissions, splatter due to overdriving amplifiers, or incorrect roll-off settings. Spectrum checks help prove you were “loud enough” without being “too wide.”

Practical checks to perform:

• Occupied bandwidth: confirm the signal fits the expected bandwidth for the modulation and roll-off.
• Spectral mask compliance: confirm shoulders and out-of-band emissions are within expected limits.
• Spurious emissions scan: look for harmonics or unexpected tones caused by equipment faults.
• Compression indicators: watch for regrowth that suggests the HPA is being driven into nonlinearity.

These measurements are most useful when captured with consistent analyzer settings and tied to the exact station configuration used during transmission.

Building a Repeatable Procedure: Calibration and Uncertainty

A verification method is only defensible if it is repeatable and calibrated. Even simple measurements have uncertainty: instrument accuracy, coupler tolerance, cable loss variation, and temperature effects all add up. The goal is not perfect precision; it is a consistent method with known limits.

Practical steps that improve credibility:

• Document the measurement chain: where the sample is taken, what attenuators are used, and what instrument settings apply.
• Maintain calibration records: instruments, couplers, and reference loads should have known calibration dates and intervals.
• Use a standard test signal: a consistent carrier or waveform makes trend analysis possible.
• Track uncertainty: maintain a simple uncertainty budget so you can state results with realistic bounds.

Stations that do this well can explain not just “what we measured,” but “how confident we are” and “what could affect the number.”

Evidence Capture: What to Record for a Credible Proof Package

Evidence should be designed for two audiences: operators who need to troubleshoot quickly, and reviewers who need to verify compliance. The best evidence is complete enough to stand alone, without requiring someone’s memory of what happened.

A practical proof package usually includes:

• Time markers: start and end times of transmission, plus the time standard used.
• Transmission parameters: frequency, polarization, symbol rate, modulation, coding, roll-off, and intended bandwidth.
• Power settings: HPA output level, attenuation states, and any automatic level control status.
• Measurement results: conducted power readings and/or received power readings with units and reference points.
• Spectrum snapshots: pre-transmit baseline, during transmit, and post-transmit comparisons.
• Station configuration state: equipment identifiers, active path routing, and profile versions.
• Operational context: which pass, which satellite, and whether the event was routine or exception handling.

When possible, capture both numeric results and a visual snapshot (such as a spectrum view) tied to the same timestamp. This reduces ambiguity later.

Logging and Recordkeeping: What to Store and How to Structure It

Logging should be structured enough that you can answer questions later without searching through freeform notes. A good logging design makes it easy to find what happened on a specific pass and to compare it to previous passes.

Recommended log fields

• Pass identifiers: satellite, contact window times, station, antenna, and scheduled activity.
• Transmit event records: exact times of enable/disable, profile applied, and operator or automation trigger.
• Power measurements: value, units, reference point (sample port location), and instrument used.
• Computed EIRP: inputs used (losses, gain) and the resulting value with uncertainty bounds if available.
• Spectrum records: analyzer settings and stored snapshots linked to the event.
• Exceptions: deviations from normal procedure, overrides, and justification notes.

Retention and accessibility

Decide how long to retain evidence based on operational needs and compliance expectations. Keep in mind that interference investigations can happen well after an event. Evidence should be stored in a way that preserves timestamps and prevents later edits without traceability.

Common Pitfalls and How to Avoid Them

Many EIRP verification problems are not technical; they are process gaps that make measurements hard to trust later. Avoiding common pitfalls improves both performance and defensibility.

• Unclear reference point: record where power was measured (HPA output, coupler, near feed) so numbers are comparable.
• Stale loss and gain values: update models after hardware changes and periodically validate cable and waveguide losses.
• Receiver saturation: over-the-air setups can produce misleading readings if the reference receiver is overloaded.
• Inconsistent analyzer settings: changing RBW/VBW and detector modes can make “before vs after” comparisons meaningless.
• No pre/post baselines: a baseline snapshot helps show what changed when the uplink started.
• Missing time discipline: evidence loses value if timestamps cannot be trusted or correlated across systems.
• Evidence stored only as screenshots: screenshots help, but structured numeric logs make audits and trend analysis far easier.

The most effective programs treat EIRP verification as a routine operational product: standardized, repeatable, and easy to review.

Glossary: EIRP and Verification Terms

EIRP (Effective Isotropic Radiated Power)

The equivalent radiated power of a transmitter when antenna gain and system losses are included, referenced to an isotropic radiator.

Conducted measurement

A power measurement taken in a cable or waveguide path, not through free space.

Over-the-air measurement

A measurement of the radiated signal using a separate receiving setup that observes the transmission in free space.

Directional coupler

A passive device that samples a small portion of RF power for measurement while leaving the main signal path intact.

Occupied bandwidth

The bandwidth that contains most of the signal’s power, often used to verify that a transmission is not wider than expected.

Spectral regrowth

Widening of the transmitted spectrum, often caused by amplifier nonlinearity or overdrive.

Uncertainty budget

A simple accounting of measurement errors and tolerances used to estimate how accurate a measurement is.

Proof package

A set of logs and snapshots that documents configuration, measurements, and timestamps for verification and audit purposes.