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Robot Mower External Antenna

This guide is intended to help owners of robotic mowers understand how to extend the base station / mower signal range, by fitting a robot mower external antenna. Actually, the antenna only needs to be fitted on the base station, as the device itself just needs to receive the signal. Other articles have covered the placement of the charging (base) station, and installation of the boundary wire. These topics are also important for a successful installation. 

The base station communicates with the mower through a signal transmitted through the boundary wire. But the mower is not always in range of the boundary wire, so the installation also relies on a weak radio signal from the base station to the mower, a bit like the signal between a cordless phone handset and its cradle. Similarly, there is a limited range to this signal, about 50m maximum, under good conditions. 

But there must be a direct line of sight between the base station and the mower for this to work properly. If structures or topography get in the way, the signal range may be reduced, or blocked altogether. Also, very importantly, this signal is relevant only when it is needed, which is upon starting the mower, or if it gets into a situation of difficulty where it has to extricate itself. Once the mower has started, and is running inside the boundary wire, the signal is less relevant. 

robot mower wire diagram

Every Yard Is Different

The standard mower setup cannot possibly cater for all conceivable yard layouts. Some yards are flat and square (or well bounded), but others come in several parts (eg. front/back/side), with structures that may get in the way between the mower and the charging station, creating ‘blind spots’. Our article on placement of the charging station addresses this issue.
Some lawns are also undulated, causing blind spots to exist for the signal between the mower and base station because of topography. However, where there is a problem to solve, we are up to the challenge! This article explains how this is overcome.

Signal is good up to 50 metres, in ideal conditions

The Signal Is Important

 
The mower receives a low strength RF (Radio Frequency) signal. It’s the kind of signal used by cordless phones, wireless WiFi routers, baby monitors, and even mobile phones. In the case of the mowers, the signal is one-way, unlike with cordless phones for example. The mower is paired to its base station, and needs to be able to receive a signal in order to be able to operate.
 
Note that it it not critical for the mower to be able to receive a signal from the base station at all times. The important times for the mower to be able to receive a signal are:
  • When it is being turned on away from the base station
  • When it experiences an exceptional fault (eg. out of bounds, current overload, etc…)
On installation, test the signal strength at various distances from the base station, by turning on the mower, and checking for the signal icon in the mower display.
 
Installing an external antenna to the base station can help increase the range of the signal transmitted.
 
 
robot mower wire diagram

My Yard Has Trees And Flower Beds

 
The radio signal can get through soft vegetation and hedges. However, thick tree trunks and branch systems will act like structures in blocking the signal.
 
On installation, test the signal strength through various obstacles, by turning on the mower, with the obstruction between the mower and the base station, and checking for the signal icon in the mower display.

My Yard Is Uneven

 
The topography of the ground can also impact on the quality of the RF signal. As with solid structures and trees, the radio signal from the antenna inside the base station won’t penetrate through earth, to be received by the antenna on the mower
 
What may be needed in these circumstances is an external antenna.

Why An External Antenna?

 

The internal RF antenna within the base station is, by necessity, very close to the ground.  As can be seen above, having an antenna that is close to the ground is sometimes not optimal. 

In environments where the ground undulates, or has various levels, It is useful to be able to raise the base station antenna to a point where the signal may reach all areas of the yard. 

That’s where an external antenna comes in. Further, the signal may be improved because the eternal antenna may have more gain than the basic wire provided within the base station

Fitting The Antenna

 
The antenna that comes with the base station is a simple wire, about 10cm long, which is soldered on to the base station PCB (circled in yellow). Because it is inside the base station enclosure, and connected directly to the board, there is no need for it to be shielded.
 
If we are to fit an external antenna, it is necessary to use shielded coaxial cable. Therefore, this wire needs to be removed, and the coaxial cable needs to be attached (soldered) onto the PCB.
 
The positions for attaching the shielded coaxial cable to the PCB are shown in the picture (circled). The core wire is attached to the last pin on the ‘card’ at the end of the PCB. the shielding, or sheath is attached to the second last pin. Care should be taken, because the two pins are very close together.
 
We have used small (5mm) coaxial cable in this exercise (a length of about 20cm is recommended), fitted with SMA connectors to allow the antenna to be attached and removed easily. 
 
 

Modifying The Base Station

 

Once the coaxial cable, with a small SMA connector on the end, is attached to the main PCB, it is then necessary to pass it through the base station enclosure. 

This can be easily achieved by drilling a small hole at the back of the enclosure, beside the boundary wire connectors, and passing the aerial SMA connector through the hole (as pictured, internally, and externally).

This hole will be sheltered by the same extrusion that shelters the power cable connector and boundary wire cable connectors.

What Size Antenna?

 
We have tested 3 different size 433MHz Signal Booster Wireless Antennae for their effectiveness:
 
  • 5dBi (12cm long). This antenna improved signal strength out to about 60 metres.
  • 7dBi (14cm long). This antenna improved signal strength out to about 70 metres.
  • 12dBi (27cm long). This antenna did not improve signal strength (it may have been faulty).
 
Therefore, the best antenna we found to be the 7dBi (14cm long).
 
 

Conclusions

Robotic Mowers conventionally use a Radio Frequency signal from the base station to the mower, as an element of control of the mowing installation. 

In some circumstances, such as where there are structures separating mowing areas, or undulations in the topography, the standard fittings of an antenna internalised in the base station may not be optimal.

It is possible to fit an external antenna to the base station in order to extend the range of the signal, and/or cater for obstacles, or undulations in the yard. 

We have found through testing that a 7dBi antenna is optimal to extend the range of the signal. The antenna may also be placed in an elevated position to adjust for changes in levels of the yard..

Do You Want to Find Out More?

If you would like us to discuss the suitability of our devices to your situation, please just fill out the enquiry form below. Alternatively, if you would prefer to speak to us first, please call us on 1 3000 ROBOT. (1 3000 76268)

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