Air-Check Verification (Off-Air Self-Monitoring)

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Air-Check Verification (Off-Air Self-Monitoring)

An air-check confirms that an alert this station sent was actually heard back off the air. It closes the loop between "the encoder generated a valid SAME header" and "that header left the transmitter intact".

UI: Diagnostics → Air-Check (/air-check)

How it works

  1. Every SDR receiver has a role (Monitor → Receivers → edit → Role):
    • Monitor (default): listens to an upstream source (NWR, LP-1, a state relay). Its decodes are FIPS-filtered and may be relayed.
    • Air-check: tuned to this station's own transmitter. Its decodes are compared with what the station sent and are never relayed, so monitoring your own output cannot loop it back onto the air.
  2. Every transmission opens an air-check. Automatic CAP broadcasts, relayed off-air alerts, manual Broadcast Builder sends, Required Weekly Tests and resends all record the exact SAME header as it starts playing. The record's deadline is the playout length plus relay lead-in/lead-out plus the grace period (default 60 s, adjustable on the Air-Check page).
  3. The air-check receiver's decode is compared field by field: originator, event code, location codes (in any order), purge time, issue time and station ID.
Status Meaning What happens
Verified Heard back with every field matching INFO entry in the system log
Mismatch Heard back, but at least one field differs (the page lists which) ERROR logged; included in health alerts
Missed Not heard by the deadline ERROR logged; included in the compliance health-alert email / SNMP trap
Unexpected A header heard on your transmitter that this station did not send WARNING logged; included in health alerts
Pending Sent, waiting for the decode Swept to missed every 30 s once past its deadline

A decode must agree with a sent header on at least three of the six fields to count as the same transmission. Anything less is recorded as unexpected.

When no receiver has the Air-check role, nothing is recorded and no errors are raised. The feature is inert until you assign that role.

Setting it up

  1. Put an SDR on an antenna that hears your own transmitter (a separate receiver, not the one monitoring your upstream source).
  2. Monitor → Receivers → add or edit that receiver, tune it to your frequency, enable Audio Output, and set Role to Air-check.
  3. Send a test (Diagnostics → Weekly Test Schedule → Send Test RWT Now).
  4. Open Diagnostics → Air-Check. The RWT should show as verified within seconds of its EOM.

If a known-good transmission shows as missed but later flips to verified with the note "heard after the deadline", your air chain has more delay than the grace period allows. Raise the grace period on the Air-Check page.

Acknowledging problems

Missed, mismatch and unexpected rows count as open problems in the 24-hour summary and in the health-alert emails until someone clicks Acknowledge. Acknowledged rows stay in the history.

Notes and limits

  • Air-checks run in the audio service (eas-station-audio). If that service is down, nothing is decoded and every transmission will be reported missed. That is intended, because the station cannot confirm what it put on the air.
  • The decoder reports a header when it hears the EOM (end of message). If the EOM is never heard (a transmission cut off mid-message), the decoder gives up waiting after 5 minutes. By then the air-check has usually been marked missed. It then changes to verified (or mismatch) with a "heard after the deadline" note, so a missed check that later resolves this way points at a lost EOM.
  • Receiver role changes take effect in the audio service within about 30 seconds.
  • Code: app_core/air_check/ (matching, lifecycle, reporting), webapp/admin/air_check.py (page and API). Design notes: Theory of Operation → Verification & Compliance.
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This document is served from docs/guides/AIR_CHECK_VERIFICATION.md in the EAS Station™ installation.