When a Robotic Lawn Mower Reaches Your Receiver
When a Robotic Lawn Mower Reaches Your Receiver
Smart gardening promises a tidy lawn and more free time. For a radio amateur or shortwave listener, there is another requirement: the machine must live alongside weak-signal reception. A quieter garden is not much of an improvement if the receiver becomes noisier whenever the robot goes to work.
RF.Guru working definition: Common-mode current is the non-cancelling phasor-sum current in a specified set of conductors, evaluated at a defined cross-section and using a declared current-direction convention. In the intended differential transmission-line mode, the outgoing and return currents are equal and opposite, so their phasor sum is zero. When they do not cancel, the remaining current must close through another reference or return path—such as the outside of a coax shield, a mast, equipment chassis, station wiring, nearby structures, earth, the operator, or distributed coupling through the environment.
This broader working definition is especially useful in practical antenna systems. On transmit, non-cancelling current on the outside of the coax can make the feedline and connected structures part of the radiating antenna system unless that path is intentional, clearly defined and properly controlled—for example by providing the required return path and placing a suitable common-mode choke at the correct boundary.
Segway’s Navimow brings the smart-garden question into focus: can a capable garden robot also be a good neighbour to an RF-sensitive station? Navigation accuracy and radio quietness are different engineering requirements. I would not choose a mower only by how neatly it works around the flower beds while ignoring what the complete installation does beside the receiving antennas.
Take the Navimow i-series as a concrete example of the system involved. Its manufacturer’s manual describes a battery-powered mower, charging station, satellite-positioning antenna and app, with a virtual boundary rather than perimeter wiring. That identifies components to consider; it is not a measurement of their unwanted emissions. The question here is compatibility at a receiving site, not a finding that every Navimow—or any other whole brand—is noisy.
If starting or charging the machine changes the receiver, that is a reason to investigate. Was the source the travelling mower, the stationary supply, a positioning installation, a data radio, a cable carrying common-mode current, direct field coupling into the antenna, or an overloaded receiver producing signals that were never present in the air? Answering that question gives the owner a useful choice: correct the relevant path, move the installation where appropriate, or choose equipment that better suits the site.
A Garden Robot Is an RF System
The cutting and traction motors are normally driven by switched electronics. The battery charger and docking supply contain power conversion. Control electronics contain clocks and fast digital edges. Some installations add satellite-navigation receivers, local data links, Wi-Fi, cellular or short-range radios; others use a boundary wire or other positioning infrastructure.
Those functions do not automatically make the installation noisy. They create possible generators and possible conductors. The disturbance that reaches an amateur receiver may be conducted through mains or low-voltage wiring, driven as common-mode current on a cable, radiated directly from the electronics, coupled in the near field, picked up by the antenna, or generated inside an overloaded receiver.
Intentional Radio and Unwanted Emission Are Different Questions
A data or positioning radio transmits deliberately in an assigned band under defined technical conditions. Motor-drive edges, converter harmonics, clock leakage and mode conversion are unintended emissions. A receiver may also hear intermodulation or overload products when a legal nearby transmitter is strong enough at its input.
Do not infer a radio frequency from the words “RTK” or “wireless boundary.” Implementations and regional variants differ. Read the exact model declaration and radio specifications, then compare those frequencies with what the calibrated receiver or spectrum analyser actually shows.
Do Not Convict the Mower from One Waterfall
| Observation | What it supports | What it does not prove |
|---|---|---|
| Noise follows the moving mower | The moving unit, its motor state, position or distance matters | Which internal circuit generated the energy |
| Noise remains while the mower is parked | The dock, charger, network or an always-on subsystem deserves attention | That the traction or blade motors are responsible |
| A comb changes with motor speed | A switched or rotating process may be involved | That comb spacing identifies a particular controller |
| A clamp around a complete cable shows correlated current | Net/common-mode current exists at that point | That the cable is the original generator or only radiator |
| Receiver attenuation collapses many lines | Receiver overload or mixing may contribute | That the external disturbance has disappeared |
Distance is useful but not sufficient. A moving unit changes distance, orientation, motor load and its capacitance to soil and nearby conductors at the same time. A dock test changes a different set of variables. The clean comparison is a sequence of controlled states, not a walk past the antenna followed by a brand conclusion.
Build an A/B/A Test Around Operating States
- Freeze the receiver. Record frequency, bandwidth, detector, preselector, gain, attenuation, AGC, averaging and antenna. Keep a wanted signal in view so a falling noise trace is not mistaken for improved SNR.
- Record the baseline twice. Measure before the mower state changes and again after it is restored. If A does not return, another source or propagation change entered the experiment.
- Separate safe user states. Compare the installation idle, mower travelling without cutting where supported, cutting, returning, docked and charging. Do not defeat interlocks or enter service modes not intended for the user.
- Map position. Repeat at several mower and dock positions. Note distance and orientation rather than relying on memory.
- Probe the paths. Use suitably rated non-contact current or near-field probes on safely accessible external cables and stationary equipment, away from the mower’s operating area. A single cable point can sit near a current minimum.
- Check the victim. Insert known receiver attenuation or suitable preselection. A disproportionate collapse of many unrelated lines points toward receiver nonlinearity.
- Change one remedy. Reroute an accessible lead, increase separation, test an approved external clamp-on ferrite or relocate the dock, then restore the baseline and repeat.
Follow the exact mower manual: keep people and probes clear while it operates; stop the machine and wait for moving parts to stop before approaching it. Switch off and isolate the relevant equipment as the manufacturer directs before fitting ferrites, rearranging cables or relocating the dock. Never open a mains supply, battery pack, charger or mower assembly for an amateur interference experiment. Do not disconnect protective earth, safety interlocks or protective conductors. Source-side filtering or internal modifications belong with the manufacturer or a qualified service technician.
Ferrite Helps Only When It Meets the Current
A ferrite choke can add useful frequency-dependent impedance to an unwanted common-mode path. That statement contains the limits: there must be measurable common-mode current, the finished choke must provide suitable complex impedance at the frequencies of interest, and its location must intercept the path.
A fixed recipe based only on material number, hole size and turn count is not portable across cables or frequencies. Winding capacitance, cable bundle, core dimensions, existing path impedance and placement matter. Treat a clip-on as an A/B/A experiment, not as a compliance repair. On a mains lead, any external ferrite arrangement must preserve the complete approved cable and protective conductor; never choke or interrupt protective earth separately.
Compliance Limits and Weak-Signal Reception Are Not the Same Test
EU equipment rules require an appropriate conformity assessment. For equipment within the Radio Equipment Directive, Article 3 includes electromagnetic compatibility as well as safety and spectrum-use requirements. Other equipment may fall under the EMC Directive. The applicable standards depend on the equipment and functions; a list of standard numbers is not a universal test plan for every mower package.
Emission and immunity tests answer different questions. Both use specified configurations and criteria. An amateur station can still detect a disturbance below an applicable emission limit because its antenna, bandwidth, location and weak-signal objective differ from the compliance test. That is why regulatory conformity and suitability beside your receiving installation both matter.
The reverse is equally important: a loud receiver trace does not by itself establish a legal violation. Preserve time-stamped screenshots, exact frequencies, receiver settings, antenna, distance, operating state and restored-baseline results. Give the manufacturer or installer a reproducible case. In Belgium, unresolved harmful interference can be reported to BIPT’s National Spectrum Monitoring Department.
Buying Advice for an RF-Sensitive Site
Whether the shortlist is Navimow, Husqvarna Automower, Ambrogio, Kress RTKn or STIHL iMOW, I would make reception part of the buying decision. Those names are alternatives to investigate, not an RF ranking. Ask for a demonstration or agreed trial of the exact mower, dock, supply and positioning accessories at your site. Scan while travelling, cutting, returning and charging. Repeat the baseline after each state and compare wanted-signal SNR, not only a colourful noise floor.
A wired boundary, satellite-guided system or radio link can each be implemented well or badly. Removing a perimeter wire removes that particular conductor, not the electronics or charging cables. Conversely, a wired system is not automatically quiet. Keep the charging installation and its wiring away from receiving antennas, masts and radial systems as far as the site and manufacturer’s installation requirements allow. Separation and sensible routing are useful design choices, not substitutes for effective suppression at the source.
My preference is straightforward: choose the installation that preserves useful reception in the bands and operating states you actually use. If one candidate creates repeatable interference and another does not in a comparable site trial, that is a meaningful advantage for your station—even without declaring an entire brand good or bad.
Practical Conclusion
The lawn mower is no longer just a motor with a blade. It is a mobile switched-power and radio system operating close to an unusually sensitive receiver. That makes it worth testing before purchase and worth investigating carefully when the waterfall changes.
I would not trade a carefully maintained receiving environment for unattended mowing without checking that the two can coexist. If the installation degrades reception, give the supplier a reproducible case and ask for a safe, effective remedy. If it cannot be made suitable, choose a different installation or machine. The point of the measurements is to protect the signals you came to hear—not to excuse an avoidable noise source beside the antenna.
Primary Standards and Official Guidance
- Directive 2014/30/EU — electromagnetic compatibility of equipment
- Directive 2014/53/EU — radio equipment placed on the EU market
- CISPR 14-1:2020 — RF-emission requirements for appliances, tools and similar apparatus
- CISPR 14-2:2020 — immunity requirements, including robotic-equipment test conditions
- ETSI EN 301 489-3 V2.3.2 — EMC conditions for short-range radio devices
- BIPT — reporting a radio-interference problem in Belgium
Mini-FAQ
- Do all robotic lawn mowers create radio interference? No. The result depends on the exact mower, dock, supply, accessories, installation, operating state, frequency, distance and receiving system.
- Does an RTK or wireless boundary system explain every signal? No. An intentional data radio, motor drive, charger, clock, cable current and receiver overload are different mechanisms that require different tests.
- Does a comb spectrum prove common-mode current? No. A comb suggests a periodic process or nonlinear mixing. A whole-cable current measurement and controlled state changes are needed to establish the path.
- Will a clip-on ferrite solve mower RFI? It may reduce measured common-mode current when its impedance and position suit that path. It cannot correct every direct-radiation, differential, internal or receiver-overload problem.
- Does a loud trace prove the mower is non-compliant? No. Compliance uses defined standards and test conditions. A station observation is evidence for investigation, not by itself a formal conformity result.
- What should I record before contacting the supplier? Exact frequencies, receiver settings, antenna, distance, mower and charger states, screenshots or recordings, current-probe results where available, and an A/B/A baseline that returns.