The EP3 spectrum analyser is a useful feature that allows you to “see” local radio frequencies in use.
A spectrum analyser is a specialised electronic device which senses radio signals from an antenna and displays them in an easy to understand format, usually a graph.
The EP3 has a basic spectrum analyser feature which helps identify radio traffic when designing an IPC solid set irrigation layout.
Our IPCs use the “ISM band” of frequencies in the 900MHz region. This is a popular frequency band and is very suitable for farm use.
In this example, a “quiet” location is shown on the left.
However, the right hand side shows peaks of radio traffic around channel 1 and 5. Channel 1 is particularly busy and this is to be avoided for this location when selecting the radio channel.
A tip is to monitor the display for a few minutes. Do the peaks always appear on the same channel, and are they displayed at regular intervals (eg every 30seconds)?
The IPC system does not use all of the available channels. Channel 11 to 15 are reserved as “guard channels” and not used for communication.
As part of the RF survey performed prior to an IMS project, the spectrum analyser function is used to help select a suitable channel for the IPCs to communicate on. This forms part of the farmID assigned to each system and irrigation block.
The spectrum analyser feature also helps demonstrate how far the transmissions travel from IPCs on site and from adjoining farms.
Peaks on the graph may not just be from IPCs in your area but could be any of the other local technologies using the same 900MHz frequency band.
What other devices might be using 900MHz and causing spikes on the graph?
Typical examples include radio control links, monitoring systems, centre pivot control signals, some IT/computer equipment and even certain cellular network signals.
Generally, all these systems can coexist without problems, but a badly designed or faulty radio transmitter, or a transmitter not compliant for use in New Zealand, may cause problems.
This previous article outlines the RF survey and we always recommend that (all but the simplest) projects undertake one. The survey reviews the comms feasibility, and identifies antenna mounting locations, internet access points, additional hardware requirements and variations needed.
If you are interested in performing this role for your customer projects, please email us for more details.