We recently held a webinar series covering basic Wi-Fi technology concepts as well as the tools used in wireless throughout the lifecycle.
In this post, we’ll summarise the second episode of the webinar series, hosted by Dan Jones: What is a spectrum analyser, and when do you need one?
What is a Spectrum Analyser?
A spectrum analyser measures and shows you the energy in the air. It scans through frequencies, measures how much energy it can see in each space and puts this data into bins. You'll see lines where it's sweeping through and then organising information into those bins.
Different types of spectrum analysers do this differently, and it's not just a wireless thing - thera are spectrum analysers that work on cables and other applications. With Wi-Fi, we focus on three bands: 2.4, 5, and 6 GHz, as well as the frequencies within those bands.
The spectrum analyser scans through those frequencies, sweeps through them one at a time, measures the energy in each particular space, and then shows you that information visually.
Why Spectrum Analysers are Useful?
There are two main reasons we use spectrum analysers. The first is to measure the noise in the environment. The spectrum we use for Wi-Fi is unlicensed; anyone can broadcast something on that spectrum. We can use a spectrum analyser to see how noisy the environment is.
For example, if you enter a meeting room and shut the door, it blocks out all the background noise, and now you can talk to each other calmly over the table. Whereas if you go into a bar, you can stand right next to someone but still have to shout over all the background noise. The spectrum analyser can show you what that noise - caused by, for example, microwaves, bluetooth devices and factory equipment - looks like for your wireless network.
With Wi-Fi, we're trying to get a good signal-to-noise ratio - we want the noise to be low and the signal to be high. That gives us the cleanest air to send data over, so we can pack as much data as possible into one transmission rather than having to do multiple basic transfers when we have low SNR.
Example of Onsite's real-time view with a spectrum analyser plugged in.
Practical Applications in Planning
One helpful application is within planning tools, where you can simulate the noise floor. If you know what the noise floor is, you can adjust it in your planning software to see the impact on data rates and MCS expectations when clients roam around.
High noise floors dramatically reduce client performance, while lower noise floors enable much better data rates. This is one reason why spectrum analysers are useful - they help you determine the noise floor, so that you can design around the actual conditions in a particular space.
Finding Sources of Interference
The second main use is finding sources of interference. Spectrum analysers are most commonly used in 2.4 GHz environments. With only three non-overlapping channels available, this band faces significant interference from baby monitors, microwaves, Bluetooth devices, and remote-control vehicles. These devices operate in the same spectrum and create substantial noise and interference issues.
In 6 GHz, this is less of a problem. In 5 GHz, it's not a significant problem, except for the UNI-3 band (the top channels), where you may see things like presence sensors. You would see short spikes in that space when you walked into a room.
Now that we've mostly retired 2.4 GHz for only IoT devices and information for devices using the 6 GHz band, it's generally seen as a "best effort" band where critical real-time data isn't necessary. The increased noise floor and retry rates become less problematic, especially as we shift our ‘everyday’ client traffic to 5 GHz and 6 GHz.
How Spectrum Data Works
When you plug in a spectrum analyser, like the Oscium Lucid, to the Nomad, you'll see the raw energy in the air and see exactly what is going on. You can also see what's called the noise floor - the background noise that's happening all the time.
Non-Spectrum Spectrum View: Without a spectrum analyser, Hamina provides a "non-spectrum, spectrum view" that displays channels and access points using colours and ziggurats to indicate how busy each AP reports its channel to be.
Example of the "non-spectrum spectrum view". Hamina Onsite and Oscium Nomad can give you an idea of how busy each channel is, even if you don't have a compatible spectrum analyser handy.
What Clients Actually Use
Your iPhone, laptop, and other devices don't have spectrum analysers built in. Instead, clients use the QBSS load information from access points. When APs broadcast their network details, such as the network name and what channel they're on, they also include information about how busy they currently are.
This information helps clients make better decisions about which AP they should connect to, since in Wi-Fi, it's the clients that make those decisions. The client looks for an SSID and gets responses back from multiple APs. If there are multiple APs above the threshold set (between -70 & -75 dBm) that the client might want to connect to, how do they decide?
In the past, clients would simply connect to the loudest signal, but that's not always the best choice. An AP right next to you might have excellent signal strength and good SNR, but if it's busy 50% of the time, you'll have trouble sending and receiving data. A more distant AP with lower signal strength but still adequate SNR and only 2% utilisation will likely give you much better performance, even though it's further away.
When Do You Actually Need a Spectrum Analyser?
So, do you need a spectrum analyser? For 99% of modern designs, probably not. Modern, smart APs will quietly hop away from bad channels long before users notice.
Some environments, like manufacturing facilities, have large equipment that produce electromagnetic interference. This creates a higher noise floor that won't break your network design, but it will affect what data rates your clients can achieve.
Is a spectrum analyser necessary for this? Not always. For measuring noise floor, it's helpful to input this data into design tools to give more realistic expectations for data rates, but it's not essential in most cases.
Spectrum analysers become more important when you have significant interference affecting entire blocks of channels. In manufacturing environments where interference makes certain channels unusable, spectrum analysis helps identify these problem areas, so you can exclude those channels from your design.
This scenario is becoming less common as vendor RRM systems improve. Modern access points have more processing power and smarter algorithms, so they automatically move to cleaner channels to avoid competing with non-Wi-Fi interference.
Key Takeaways
In most modern deployments, spectrum analysers are no longer essential tools. For 90-99% of environments, particularly offices and hospitality settings, good RRM systems eliminate the need for dedicated spectrum analysers. Access points automatically move away from problematic channels to cleaner frequencies.
The focus has shifted toward using the intelligence already built into access points. As vendors continue to improve their RRM algorithms with better automation and smarter spectrum management, the need for external spectrum analysis tools continues to decrease.
