Wireless Surveys · Topic 2 of 2
Spectrum Analysis and Prediction Software
Learn how spectrum analysers reveal non Wi-Fi interference, how prediction software models coverage from floor plans, and why both need an on site check.
- 5 min
- A spectrum analyser measures raw energy, so it sees non Wi-Fi interference that a Wi-Fi scan cannot.
- A waterfall shows energy over time, and duty cycle shows how busy a frequency is.
- Microwave ovens, video senders, cordless phones and Bluetooth are common non Wi-Fi sources.
What it is
Spectrum analysis shows the radio energy on each frequency, and prediction software models how a design will cover a building.
They answer two different questions. Spectrum analysis asks what is already in the air. Prediction asks what a planned design will do.
Neither replaces a survey on site, but both make the survey faster and better targeted.
How it works
An analyser measures the real environment, and prediction software builds a model of the future one.
Spectrum analysis
A normal Wi-Fi scan hears only Wi-Fi networks. A spectrum analyser measures raw radio energy, so it also sees devices that do not use Wi-Fi.
Typical sources of non Wi-Fi interference are microwave ovens, video senders, cordless phones and Bluetooth devices.
What an analyser shows
Analysers show the energy in several ways.
| View | What it shows |
|---|---|
| Live graph | The energy at each frequency right now |
| Peak or average | The highest or typical energy seen over time |
| Waterfall | Energy over time, drawn as colour |
| Duty cycle | The share of time that each frequency is busy |
Different patterns point to different sources.
A steady wide band of energy can be a video sender. A short regular burst can be a microwave oven. A narrow band that hops around is typical of Bluetooth.
Spectrum tools in RouterOS
Some MikroTik radios can run a spectral scan on the legacy wireless package, and there are also frequency monitor and snooper tools.
/interface wireless spectral-scan wlan1
/interface wireless frequency-monitor wlan1spectral-scanshows the energy across the band, on hardware that supports it.frequency-monitorshows how busy each frequency is over time.
Not every radio supports the spectral scan. A dedicated analyser gives more detail and does not interrupt the access point. A scan on a live radio interrupts service.
Use the analyser to find a quiet part of the band before you set the channel plan.
How to use the results
Use the readings to act.
- Move the network to a quieter channel.
- Switch to 5 GHz if 2.4 GHz is crowded with non Wi-Fi noise.
- Remove or relocate the interfering device if you can.
- Narrow the channel width to leave room.
Prediction software
Prediction software builds a model of the building and shows the expected coverage before you install anything.
The usual workflow is:
- Import the floor plan and set the scale.
- Mark the walls and set their materials, because each material weakens the signal differently.
- Place virtual access points and set their power, antenna and channel.
- View the coverage as a heat map.
- Adjust the number and position of the access points until the targets are met.
The heat map uses colour to show the expected signal strength in each area. It can also show the overlap between channels and the areas that do not meet the target.
Strengths and limits
Prediction is fast and cheap. It lets you compare designs and estimate the number of access points before you visit the site.
It is only a model. Wrong wall materials, furniture and people that the model does not know about all change the real result. The model also cannot see your neighbours or other interference.
| Tool | Strength | Limit |
|---|---|---|
| Prediction software | Fast, and useful before any visit | Only as accurate as its inputs |
| Spectrum analyser | Sees non Wi-Fi interference | Shows the air, not the design |
| On site survey | Measures the real result | Takes time and needs access |
Outdoor planning
For long links, planning software uses terrain data to draw a path profile. It shows the obstacles and the height needed to clear them. As with indoor work, the real path should be checked on site.
Never accept a prediction as proof. Verify the design with an on site survey, because a model cannot know the real building.
What to remember for the exam
Seven facts cover this topic.
- A spectrum analyser measures raw energy, so it sees non Wi-Fi interference that a Wi-Fi scan cannot.
- A waterfall shows energy over time, and duty cycle shows how busy a frequency is.
- Microwave ovens, video senders, cordless phones and Bluetooth are common non Wi-Fi sources.
spectral-scanneeds supported hardware, and scanning a live radio interrupts service.- Prediction software models coverage from a floor plan and wall materials.
- A heat map shows the expected signal strength.
- A prediction must be verified on site.
Common mistakes
These four errors are common.
Using a Wi-Fi scan to find all interference. It cannot see devices that are not Wi-Fi.
Entering wrong wall materials. The prediction then does not match reality.
Treating a prediction as final. It is a model and must be checked on site.
Scanning a busy radio. The clients lose service while it runs.
Check yourself
Work through these three questions.
Why can a spectrum analyser find interference that a Wi-Fi scan misses?
It measures raw radio energy, so it sees devices that do not use Wi-Fi, such as microwave ovens and video senders.
What does a heat map show?
It uses colour to show the expected signal strength in each area of the floor plan. It also shows where the targets are not met.
Why must a prediction be verified on site?
It is only a model and cannot know the real walls, furniture and neighbours. An on site survey measures the real result.
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