When Your Lawn Mower Becomes an Interference Source: EMC Warnings for RF Enthusiasts

The age of smart gardening has brought robotic lawn mowers into many suburban and rural homes. For most people, they offer convenience and a tidy lawn. But for radio amateurs, shortwave listeners, and anyone operating sensitive RF equipment, these devices can become an unexpected nightmare.

One brand raising increasing concern in the ham radio and RF monitoring community is Segway, particularly their Navimow series of robotic lawn mowers. While sleek and highly capable in terms of garden navigation, these mowers have shown a consistent pattern of poor electromagnetic compatibility (EMC) design.

Why EMC Matters in the Garden

Robotic mowers are not passive devices. Under the hood, they’re filled with brushless DC motors, switching power supplies, RTK positioning radios (often operating on 433 MHz or 868 MHz), Wi-Fi modules, and sometimes even LTE/4G chips. All of these components can emit radiofrequency noise, both intentional and unintentional.

In dense RF environments—urban settings, shared garden spaces, or properties with installed RX antennas—this noise is more than an annoyance. It can raise the noise floor by several dB across HF bands, obliterate weak signal reception, or even create false triggering in SDR setups.

What Makes Segway Problematic?

Reports from RF engineers and amateur operators suggest that Segway Navimow units:

• Emit noticeable wideband noise during operation, especially when motors engage
• Radiate spurious signals from the RTK base station, especially around 433/868 MHz
• Leak low-frequency switching noise into mains or garden ground paths

While some of these issues can be mitigated with better shielding, grounding, or ferrite suppression, the fact remains: Segway's current generation lacks the EMC polish found in more mature brands.

Better Alternatives for RF-Sensitive Locations

If you’re working with RX antennas—especially active E-field probes, low-band loops, or phased arrays—it’s crucial to pick equipment that doesn’t undermine your setup. Brands that have a better EMC track record include:

• Husqvarna Automower (high-end models): Well-shielded electronics and minimal motor noise
• Ambrogio: Reliable brushless systems with less aggressive PWM controllers
• Kress RTKn: Cleaner RTK integration and better isolation in tests
• STIHL iMOW: Uses a low-frequency perimeter wire (around 8–10 kHz) and is known for good EMC behaviour

STIHL vs Segway: A Quick Comparison

Feature	STIHL iMOW	Segway Navimow
Boundary System	LF wired (~8 kHz)	Wireless RTK (433/868 MHz)
EMC Behaviour	Good (quiet)	Often noisy
Known RFI Issues	Rare to none	Several reports
SDR/Receiver Compatibility	Generally safe	Often problematic

How to Mitigate RFI if You Already Own One

If replacing your mower isn’t an option, you can still take steps to reduce interference. High-quality ferrite cores on the base station and supply wiring are an effective first line of defense. We recommend the Type 31 split-core ferrite (25 mm ID). For best results, loop the cable through the core multiple times:

• 5 turns on the main power cable close to the mower’s charging base
• 5 turns on the power cable near the AC adapter/transformer
• 5 turns on the sensor wire leaving the base (one direction)
• 5 turns on the return sensor wire (opposite direction)

This creates strong common-mode suppression across the HF and VHF ranges, lowering conducted and radiated noise significantly.

Practical Advice Before You Buy

• Ask for a demo period: Test the mower near your antennas before finalising a purchase
• Scan with an SDR: Check for broad-spectrum emissions while the mower runs and charges
• Avoid installing the charging base near radials or antenna masts

Conclusion

As ham radio operators, we don’t just operate transmitters—we maintain a delicate environment for receiving weak signals. A poorly filtered robotic mower can compromise that entirely. If you’re planning on installing any RX infrastructure, especially phased arrays or active antennas, make sure your lawn equipment isn’t your worst enemy.

Choose wisely—and listen quietly.

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