How to perform a Site Survey

Create a separate SSID for the 2.4 and 5 GHz bands while performing a site survey. This makes it easy to know where you’re at while testing.

Once the site survey is complete, we recommend giving both SSIDs the same name to make it easier for the customer to use. This avoids confusion and potential Technical Support calls. (SSIDs can use the same name without interfering with network communications.)

If you, or the customer, decide to keep them separate, make sure the customer knows the difference between the two SSIDs.

Pro Tip: Do not permanently mount devices until the site survey is complete.

There are 2 parts to performing a proper Wireless Site Survey:

  1. Surveying the Signal Strength from AP to AP
    This helps you approximate the proper mounting locations for the APs in your system.

  2. Surveying the Signal Strength from AP to Client Device
    This is the most important value. Do your best to keep this signal from getting too weak so you have enough signal to maintain high bandwidth data transfers from the client device to the AP.

Units of measurement

Signal strength can be measured one of two ways: RSSI (received signal strength indicator) or dBm. Depending on the application being used, it’s good to know how these units of measurement differ.

  • RSSI is a relative unit of measurement that depends on the device’s Wi-Fi card.

  • dBM is an absolute unit of measurement, using mW (milliwatts).

Wi-Fi signal strength is measured in signal loss, meaning that the value is a negative number. The closer you are to zero the better, though you’ll rarely see a measurement better than -30.

Surveying the signal strength from AP to AP

Most APs typically provide a feature to scan the surrounding area for other APs. For specifics on the feature, see the AP’s user manual. Below are the basics to finding approximate mounting locations for your APs.

Place the first and second APs in temporary locations, then perform a scan from the first AP.

The next AP should be at an RSSI of between -65 and -70 dBm. Move the second AP closer if the signal between them is too weak, and further away if the signal is too strong. This should put the APs at a rough distance that provides adequate signal to a client device that is between them, which is why we’ll be surveying the signal from the AP to the client device next, using a Wi-Fi analyzer app.

Note: APs have much stronger radios than a client device does, so -70 dBm from AP to AP is much different than -70 dBm from AP to client device. The target range of -65 and -70 can be debated, but this range is what our support team finds most helpful to find an approximate AP location. Surveying the signal from AP to client device gives you more defined values for final placement.

Surveying the signal strength from the AP to the client device

Install a Wi-Fi analyzer app on your device. A quick search for “Wi-Fi analyzer” in the Google Play provides plenty of options. For iOS, use their AirPort Utility app. We’ve partnered with MetaGeek for their Wi-Fi tools that include a spectacular Wi-Fi analyzer, which measures in dBm.

A Wi-Fi analyzer app displays the wireless signal strength from all the APs broadcasting in your area. The results that are displayed are very similar to the results seen in the scans done in the AP but are provided in real time, and adjust as you move with the device running the analyzer app.

In a multiple-AP deployment, stand directly between the two APs with the Wi-Fi analyzer app running. The target values are:

  • 5GHz Targetof -65 (RSSI or dBm)

  • 2.4GHz Targetof -70 (RSSI or dBm)

Note: The unit of measurement depends on the application being used.

Maintaining these target values between APs ensures you’re not losing too much signal from the AP, resulting in a strong Wi-Fi connection and consistent data transfer rate. For this reason, you want to make sure that your 5 GHz device never falls below this value at any point in the system.

Why these values?

Client device manufacturers typically set their roaming threshold to about -65 through -70 dBm. For this reason, we suggest a 5 GHz target of -65 dBm to account for the most sensitive devices.

You may have noticed that the 2.4 GHz target is lower. This is for a few reasons:

  • 2.4GHz devices do not typically require high data transfer rates.

  • If a device does require high data transfer rates, it can most likely use a 5GHz connection.

  • Devices prefer the strongest signal they see.

  • If the 2.4 GHz RSSI is weaker than the 5 GHz RSSI at the roaming point between APs, the 5 GHz signal is always preferred.

Note: Roaming behavior is dependent on the client device manufacturer. Some devices prefer a 5GHz signal, some look for the strongest signal available and may move between 2.4 and 5GHz. Not all devices are 5 GHz capable, so we need to accommodate those devices, as well.