DFS radar events: understand before you fix
Dynamic Frequency Selection (DFS) lets Wi-Fi networks share part of the 5 GHz band with priority users such as radar systems. When an access point detects what it considers a radar signature, it must stop using that channel. Before transmitting on a DFS channel, it may also have to run a Channel Availability Check (CAC), whose duration depends on the frequency range and the applicable regulations.
For users, the effect ranges from a brief interruption to a reconnection, a BSSID change or a visible drop in real-time applications. It depends on the vendor, the architecture, the new channel and the backup coverage offered by neighbouring access points. A “radar detected” log entry confirms that the mechanism fired; it does not prove the nature, location or duration of the signal received. Conversely, a one-off spectrum measurement that shows nothing cannot rule out an intermittent event.
- Build a single timeline: controller events, affected radios, channels before and after, user complaints.
- Separate DFS moves from ordinary RRM/DCA channel changes, access point reboots and client roaming.
- Check the backup coverage available when a radio has to leave its channel.
- Use continuous, time-stamped monitoring when events are rare.
Removing every DFS channel is rarely the right reflex: it reduces the number of usable channels and can increase co-channel contention, especially in dense environments. Depending on the business impact actually observed, the answer may be an adapted channel plan, different channel widths, targeted densification or the 6 GHz band.
Roaming drops: the client decides
In Wi-Fi, the client device usually decides when to leave its access point and which BSSID to join next. Two devices in the same spot can behave differently depending on their chipset, driver, operating system and power-saving policy. The infrastructure’s job is to offer consistent cells, enough secondary coverage and candidates that are genuinely usable: the device needs a good reason to leave, and a good place to go.
Raising every transmit power often makes “sticky” clients worse: the device keeps hearing the distant cell while its own uplink gets harder. 802.11k (neighbour reports), 802.11v (transition hints) and 802.11r (faster transitions) help a mobility design that is already sound, but they replace neither secondary coverage, nor a coherent power plan, nor validation with the devices actually in use. And a drop on the move is not always a roaming problem: authentication, DHCP, the wired network or the application can be the real cause.
- Measure RSSI, SNR and secondary coverage along the real routes where drops occur.
- Compare transmit powers, cell sizes and the availability of neighbouring BSSIDs.
- Check client capabilities and the 802.11k/v/r configuration.
- Time each step: radio link loss, reassociation, authentication, IP connectivity, application recovery.
For Wi-Fi voice, barcode scanners and industrial terminals, validation must use the production model on the actual routes: a tolerant laptop proves nothing for a more constrained business device.
When does a self-assessment stop being enough?
A questionnaire points to symptoms; only measurement shows the cause. An on-site survey is usually worth it when:
- drops or slowdowns keep recurring in the same zones or at the same times;
- mobile devices such as scanners or Wi-Fi handsets lose connectivity while moving;
- your controller logs DFS events or frequent channel changes;
- the building has changed: new racking, partitions, machinery or a new use of the space;
- you are preparing a Wi-Fi 6E or Wi-Fi 7 migration and want to size the 6 GHz target on real data.
TWN Consulting carries out site surveys and spectrum analysis with Ekahau AI Pro and Sidekick 2. Each deliverable separates confirmed facts, credible hypotheses and points that need further observation, so that decisions rest on what was actually measured. See our services for businesses →
Where to go next: an on-site Wi-Fi audit for a live network that misbehaves, a coverage study before a new deployment or a 6 GHz migration, or continuous Wi-Fi monitoring (pilot programme) for incidents that are rare or hard to reproduce.