RF Interference Troubleshooting: When the Problem Is Not the Network

Wireless problems divide into two categories that look identical from the client and have completely different fixes. Congestion is too much Wi-Fi traffic sharing a channel. Interference is energy in the band that is not Wi-Fi at all. Changing channels fixes one and can make the other worse.

Telling them apart

A Wi-Fi scanner — software on a laptop or phone — shows networks, their channels and their signal strengths. It sees only Wi-Fi, because it uses a Wi-Fi radio, and a channel that looks empty to it may be saturated by something else entirely.

A spectrum analyser shows raw energy across the band regardless of what produced it. That is the distinction: it is the only tool that reveals non-Wi-Fi interference, and it is why a site with mysterious problems and a clean scanner reading needs one.

The symptoms that point at interference rather than congestion: retransmission rates high while the number of visible networks is low, problems confined to one area or one time of day, performance poor despite strong signal, and clients connecting at low data rates with good RSSI.

Signal-to-noise ratio is the number that captures it. Strong signal with a high noise floor performs worse than moderate signal in a quiet band, and a scanner reporting only signal strength hides that.

What causes it

Microwave ovens emit strongly in 2.4 GHz and are the textbook case — problems appearing at lunchtime in an office near a kitchen is the classic pattern, and it is recognisable from the timing alone.

Cordless phones, wireless cameras, video senders and baby monitors occupy the same bands, frequently continuously.

Bluetooth hops across 2.4 GHz and contributes noise in dense environments, which is a further argument for treating that band as legacy.

Wireless presentation and headset systems in meeting rooms, which nobody counts as network equipment.

Industrial and medical equipment — welding gear, induction heating, some diagnostic machinery — which can be powerful and intermittent.

Poorly shielded electronics and failing fluorescent ballasts, which produce broadband noise rather than a clean signal.

Weather and airport radar, which triggers dynamic frequency selection on 5 GHz and causes access points to vacate channels abruptly — a brief outage that looks like a fault and is the radio behaving correctly.

And deliberate jamming, which is the denial of service case discussed under physical and environmental attacks.

A diagnostic order

Confirm it is wireless at all. Test the same task on a wired connection at the same location, because a great many "Wi-Fi problems" are server, internet or application problems.

Check whether it is location-specific, time-specific or client-specific. A problem affecting one device type points at drivers or a client capability rather than the environment.

Look at the controller's own statistics — channel utilisation, retry rates, noise floor per access point. Modern platforms report all of it, and it is frequently enough to identify the affected area without visiting.

Then survey with a spectrum analyser in the affected area, at the affected time. Interference that appears only when a machine runs will not be found by a survey conducted on a quiet Sunday.

Fixing it

Remove the source where possible, which is the only complete fix. Replacing a wireless presentation system or relocating a microwave is cheaper than redesigning a network around it.

Move away from it in frequency — to a different channel, or better to 5 or 6 GHz, where most consumer interference sources do not reach. This is frequently the practical answer.

Reduce cell size and increase density, so clients are closer to their access point and the signal is strong relative to the noise. Turning power up does the opposite of what people expect, for the reasons under wireless site surveys.

Shield or relocate where the source cannot be removed.

And where the requirement is genuinely critical, use a cable. A wireless link with an uncontrollable interference source is a permanent risk, and the honest recommendation is sometimes to stop trying to fix it — the reasoning under availability objectives, where the achievable target has to match the medium.

Exam angles

Distinguish congestion (too many Wi-Fi networks sharing a channel, visible to a Wi-Fi scanner) from interference (non-Wi-Fi energy, visible only to a spectrum analyser). Know signal-to-noise ratio as the metric that captures interference where signal strength alone does not. Name microwaves, cordless devices, Bluetooth, industrial equipment and radar as sources, and know that DFS events on 5 GHz cause legitimate channel changes. Recognize moving band, reducing cell size and removing the source as the fixes.