6.2 Evidentiary Value of Logs in Interference Investigations
Key Takeaways
Records made during or soon after operation can help reconstruct the station settings and timing.
The absence of a contact log entry does not establish that a transmitter was unpowered or silent.
A complaint and the station log must use a comparable date and time basis before you compare them.
Consider transmitter emissions and receiver susceptibility. Frequency separation alone does not resolve an interference report.
Record the symptoms and relevant measurements. Pause operation that causes harmful interference.
Treat the log as evidence of what it records
A contemporaneous record is made during or soon after an event. A station log can help you recover the approximate timing, mode, power or antenna settings of a contact. An engineering note may record what was measured, which instrument was used and whether the test was into an antenna or a dummy load. A log entry can corroborate the account, and its value depends on whether the records are complete and accurate.
For an interference report, compare what the log shows with what you need to know. A contact entry does not record every transmission unless the operator has a system that actually captures every transmission. A report of an unused frequency also does not prove a station could not affect a receiver through another mechanism. A strong reconstruction explains what each piece of evidence can support.
| Observation or record | Useful question | Limit of the observation |
|---|---|---|
| An evening contact is entered at 09:12 UTC | Does this match the local time of the report? | The time zone and date need to be confirmed. |
| The recorded mode is FM | Which frequency and power quantity apply? | A selected mode and power setting do not establish what was emitted. |
| An amplifier was set to bypass | Was it in the signal path at the time? | A note about the setup may need confirmation from equipment records or tests. |
| The receiver is quiet during a later test | Does the same station configuration and receiver setup reproduce the problem? | An intermittent condition can be absent during the test. |
Worked example: a 7 MHz report during 2-metre operation
A listener reports continuous buzzing on a 7 MHz receiver at 19:00 local time. Assume the locality is on UTC+10 that day, so 19:00 local is 09:00 UTC. The amateur's log records a Standard class-licensed station transmitting F3E at 146.500 MHz from 08:57 to 09:12 UTC, at a measured 25 W mean power. Table B item 5 sets a 30 W pY limit for F3E at this frequency. That comparison addresses the Schedule 2 power question.
The log supports the reported timing overlap, even though the listed transmit frequency is far from 7 MHz. The ordinary second and third harmonics of 146.500 MHz are 293.000 MHz and 439.500 MHz. Neither is near 7 MHz. That narrows one possible explanation. It does not exclude receiver overload, mixing, a different transmitter emission or noise from unrelated equipment. A continuing buzz during a verified station-off period would be evidence to consider when checking other sources.
If the two people agree to compare observations, they can record the receiver symptoms and when the station is off, without deliberately repeating harmful interference. The operator can check the transmitter and filter on a suitable dummy load before any necessary on-air test. If there is a change to a cable, filter or source of noise, record the exact change and compare the same conditions again. Avoid claiming that the station is proved compliant merely because the power entry is within its ceiling.
Record the response
- Obtain the date, time and time zone, affected service or equipment, frequency if known, and a description of the symptoms.
- Compare that information with the station log and available equipment or measurement records. Note missing information and possible differences in configuration.
- Check the equipment and connections. ACMA's guidance includes appropriate filtering, matching, antenna placement and using only the power needed as ways to reduce interference.
- Under section 15 of the Amateur Class Licence, operation causing harmful interference must stop. If you receive a valid ACMA written notice for relevant information or documents, provide the material required in the stated way and timeframe.
For an on-air test that is necessary and can be made without causing interference, follow ACMA's operating guidance on identification, listening and minimum power. A measured observation is more useful when the record includes the equipment configuration, the time and the test conditions. Keep later corrections distinguishable from the original entries.
What can a station log written close to the time of operation contribute to an interference inquiry?
An automatic finding that the station complied with every licence condition.
A legal guarantee that every transmission was captured.
An obligation for ACMA to dismiss the complaint.
A record of reported station activity and settings that can be compared with other evidence.
A listener reports interference at 19:00 local time on a day when the site uses UTC+10. The station log shows activity from 08:57 to 09:12 UTC. What can you conclude?
There is no overlap because 19 is greater than 09.
The log proves that the station caused the interference.
The times overlap after conversion, which supports checking the station and other possible sources.
The log proves that the station was unpowered at the reported time.
What is a useful first step after a neighbour reports intermittent radio interference?
Record the time, affected equipment and symptoms, then compare those details with station activity and check the equipment.
Repeat the suspected transmission at full power until the neighbour can confirm the problem.
Assume the receiver is faulty solely because the station has a valid call sign.
Discard the station log because the affected receiver is on another band.
Sections you finish are checked off in the contents.