An Approximately-120 MHz Feature Becomes an Instrument/Path Caution

The campaign asked whether a recurrent approximately-120 MHz family was more consistent with an external environmental source, the local computer and USB environment, or the analyzer and its input path. The classification rules were frozen before the measurements, including a priority rule that terminated-input recurrence overrides environmental promotion.

The completed result is explicitly post-acquisition compatibility-amended rather than a pristine preregistered result. One accidentally extra capture was recovered and adjudicated by chronology without examining signal content; an alternate-cohort sensitivity check produced the same disposition.

The family was detected in all 15 primary traces and recurred in all five three-trace blocks. It remained present in all six traces from the two terminated-input brackets. The block-median peak coordinates ranged from 119.999664 to 120.000336 MHz; their sub-kilohertz differences are below the 1 kHz RBW context and are not interpreted as distinct emitters.

With the same antenna geometry, the powered-computer blocks showed approximately 15.0–16.532 dB more median peak excess than the powered-down antenna block. The lower-level family nevertheless remained detectable when the recorded computer, charger, hub, SDR, and USB environment was off.

• T1 terminated bracket: 3/3 detections; 119.999664 MHz median; 13.000 dB median excess.
• A1 antenna with computer/USB environment on: 3/3; 120.000336 MHz; 29.500 dB.
• B antenna with recorded computer/USB environment off: 3/3; 120.000114 MHz; 12.968 dB.
• A2 antenna after restoring the computer/USB environment: 3/3; 120.000336 MHz; 27.968 dB.
• T2 terminated bracket: 3/3; 119.999664 MHz; 12.969 dB.

Recurrence in both terminated brackets requires the family to be classified as a tinySA or input-path response candidate. The powered-computer contrast supports an additional computer/USB-state-dependent contribution, but the experiment did not isolate its physical route or establish a sole cause.

This result does not prove that every signal near 120 MHz is artificial. It establishes a narrow caution for comparable observations from this analyzer configuration, not a frequency-wide rule and not a classification transferable to the HackRF or NESDR.

The owner proposed that building electricity or wall wiring might participate, perhaps through a relation to 60 Hz. Numerically, 120 MHz is two million times 60 Hz, but that arithmetic relation is not evidence for a physical two-millionth harmonic. Ordinary mains harmonics, switching or clocked electronics, conducted or radiated coupling through wiring, and a response inside the analyzer path are distinct hypotheses that this campaign did not separate.

A future mechanism study could manipulate those candidate paths under its own preregistration. Until then, the 60 Hz and wall-wiring idea remains a hypothesis rather than a finding.

Future comparable analyzer observations inside the narrow registered family will be annotated with this caution, preserved, and subjected to controls before environmental promotion. The rule permits neither automatic masking nor automatic suppression.

The Explorer can now move to another target or region while carrying this result in its scientific memory. No transmitter, station, service, facility, modulation, message, calibrated field strength, novelty, or anomaly is asserted.