Wireless CCTV transmitters degrade a care-home Wi-Fi voice system
A 60-bed seniors' residence runs a 2.4 GHz Wi-Fi network of 12 access points carrying nurse-call tablets and a voice-over-Wi-Fi handset system. Throughput and audio were stable until a contractor installed eight wireless CCTV transmitters (2.4 GHz, 100 mW, eight selectable channels) to link corridor cameras to a recorder. Since then tablets drop association in the east wing, handsets show choppy audio, and staff report the problem worsens in the afternoon when more cameras are active. A technician with a spectrum analyzer sees the 2.400–2.4835 GHz noise floor raised by 20–25 dB across all channels, with three narrow, steady carriers spaced about 8 MHz apart; the access points' own signals look normal when the cameras are switched off. The recorder's antennas sit 30 cm from one access point. The contractor says 'Wi-Fi is designed to tolerate interference' and proposes moving the access points to channel 13.
1. The analyzer shows three steady carriers and a raised floor across the whole band. Distinguish likely in-band interference from measurement or receiver overload.
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Steady carriers: analogue video transmitters produce a continuous carrier with wide FM deviation, unlike the bursty, rate-adaptive traffic of Wi-Fi. Three carriers about 8 MHz apart fit several cameras running simultaneously on adjacent settings, and they will sit on top of the 2.4 GHz Wi-Fi channels used by the access points.
Raised floor everywhere: a 20–25 dB rise at frequencies where no camera transmits is not ordinary co-channel interference. Two explanations fit:
- Front-end overload / desensitisation. At 30 cm from a 100 mW transmitter, the receiver (and the analyzer) can see around 0 dBm or more; the input stage compresses, the noise floor appears to rise, and spurious products appear. This is an EMC susceptibility problem, not a spectrum-sharing problem.
- Broadband noise from the cameras' unfiltered switching supplies, radiated or conducted onto cabling.
Tests to separate them: insert 10–20 dB of attenuation or a band-pass filter at the analyzer input and repeat; if the floor drops, it was overload. Move the measurement antenna several metres away; switch cameras off one at a time; check whether carriers land on channels 1, 6 and 11.
2. Assess the channel-13 proposal and rank practical mitigations.
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Channel 13 occupies roughly 2.477–2.4835 GHz at the top of the band. Canadian licence-exempt operation and most client hardware are limited to channels 1–11, so many tablets and handsets will simply not use channel 13, and the camera energy still overlaps it. It is a fix that fails quietly rather than a solution.
Ranked mitigations:
- Separation - move the recorder and its antennas away from the access point. Thirty centimetres is far too close; aim for several metres and vertical offset, since this alone may remove the overload.
- Channel plan - keep access points on 1, 6 and 11 with 20 MHz width; set cameras to frequencies that do not coincide with those three.
- Change the transport - wired/PoE cameras, or 5 GHz links, remove the contention entirely and are the durable answer.
- Reduce coupling - lower camera power, use directional antennas aimed along corridors, and keep camera cabling and power supplies away from AP cabling.
Wi-Fi 'tolerates' interference only by retrying and lowering its rate. Voice is latency-sensitive, so retries arrive as choppy audio; the system does not degrade gracefully.
3. Who is responsible for fixing this, and what regulatory steps apply if it is not fixed?
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Both the Wi-Fi network and the cameras are licence-exempt apparatus, so neither enjoys protection from interference. However, the obligation not to cause harmful interference rests with the newly installed equipment and the party that installed it. The residence is entitled to ask the contractor to correct the problem, and the contractor cannot discharge that duty by blaming the Wi-Fi.
Practical steps:
- Record a baseline: spectrum plots and throughput/latency measurements with cameras off and on, at fixed locations and times.
- Put the finding in writing to the contractor, with a reasonable deadline and the proposed remedies.
- Keep the equipment on its certified settings and antennas.
- Note that the affected system supports nurse-call and voice traffic, which raises the consequence of failure and strengthens the case for a prompt fix.
If the contractor will not act and harmful interference continues, the residence or the contractor can ask ISED to investigate. Regulators expect complainants to show evidence of attempts to resolve the matter bilaterally, which is why the before/after documentation matters.