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How We Test USB Wi-Fi Adapters

Quantitative Testing

Throughput is one of a Wi-Fi adapter's key specifications. Since these are all AC1200-capable models, you might not expect much variation between them.

The router and the overall network topography remained constant throughout testing. Throughput was measured at five, 25, 50 and 75 feet. The distances were determined with a measuring tape. Fifty-foot testing included two intervening walls that were in the way due to the physical setup of the test lab. Line of sight was slightly lost at 50' as we turned a corner to get far enough away from the router. Tests reaching 75 feet go out into an open atrium just outside the suite's entrance. The setup is in the first floor of a commercial building, and the walls are constructed of plaster.

Above is a figure of the office test setup that shows the various distances, and the intervening wall structures at 50 and 75 feet. If 75-foot testing is done, the procedure puts the tested adapter outside of the office. The diagram is not to scale.

A labeled image shows the physical setup of the testing location. Note that the router on the left-hand side is standing at an upright angle.

When a router and adapter are too close together, the Wi-Fi signals can cause interference (as represented in the image above). This is why a router and an access point (AP) should not be set up in close proximity, and not on the same Wi-Fi channel.

In most cases, the speeds close to the router at the five-foot distance were slower than at 25 or 50 feet. This phenomenon can happen when the signals are too strong between the router and the adapter, creating interference as a result of being too close to each other. Simply put, this is one of those cases when a wired connection is preferred over wireless.

A screenshot of the type of data that the popular Web-based Speedtest ( generates. While it will provide an indication of the download and upload speed, it measures the Internet connection and not the wireless network speeds.

Measuring the speed of a network connection is a vital part of each adapter's quantitative evaluation. Simply running an Internet speed metric, such as, will give you the speed of the online network connection, but it's not the right test to use to compare Wi-Fi speeds. Unless you have a gigabit connection (such as Google Fiber), the throughput of a home's internal network will be faster than the Internet, invalidating the use of a Web-based tool for these tests.

A screen capture from Windows 7 showing the network speed estimate over a 5GHz Wi-Fi network; in this case it was 325.0 Mb/s.

There are better ways to approximate wireless network speed. The first is Windows' Network Center, which can provide a rough estimate of the network adapter's connection. It's not an indicator of actual performance though, so it is not the best number to use since it does not get measured directly.

For home users with multiple devices on their network, by transferring a file between two computers within a Windows Home Group, knowing the size of the file and timing the transfer time, speed can be measured and Mb/s derived. One of the devices should be wireless and the other one wired, preferably on a 10/100/1000 Mb/s Ethernet port, to best measure the wireless connection's speed. The limitation of this method is that the transfer is manually timed, introducing an element of inaccuracy (the last time I did this I was using a stopwatch app for my smartphone, practicing starting the transfer and the stopwatch simultaneously, which is difficult to perfect).

This is the raw data that IxChariot generates. Note the throughput at the 50-foot distance on the 5GHz band fluctuated significantly from a minimum of 18.5 to a maximum of 231.8 Mb/s, which, while it averaged out to 116.8 Mb/s, hardly tells the whole story!

Given the limitations of the previously mentioned techniques, a dedicated software solution was chosen: IxChariot.

This software can measure network performance in a reliable and consistent fashion, including TCP throughput. It'll report minimum and maximum speeds, as well as calculate the average. TightVNCViewer, a remote desktop software solution, is used to remotely access our ASRock server in order to log into a desktop session and retrieve the IP address. Then, TightVNCViewer is terminated. When working with IxChariot, we designate the server's IP address as Endpoint 1 and the laptop's IP address as Endpoint 2. We use the High Performance Throughput test to determine speeds that are reported in Mb/s. Throughput tests are run to completion, which means, specifically, the test is run until 100 timing records are finished and the results recorded with screenshots.

A hypothetical bar graph of the speeds obtained (x-axis, expressed in Mb/s) from four wireless AC USB adapters (y-axis). Note that the maximum speeds are in black, the minimum speeds in red and the average speeds in blue. While one product may have lower minimum values, it may not necessarily have lower averages. This same observation also applies to peaks values.

PassMark's WirelessMon is a software package we use to measure signal strength in five-foot increments on the 2.4 and 5GHz bands. The WirelessMon software provides a signal strength reading between the device under test and the router for a given distance. The notebook is held in each spot for 20 to 30 seconds to get this reading. This data set looks at how good the antenna is on the adapter, or if a manufacturer's implementation of beamforming (a Wi-Fi technology designed for directional signal transmission) is working or not, as the distance increases compared to the competition. All of this data gets put into an Excel spreadsheet with relevant notations on how the test went specifically for that USB AC1200 Wi-Fi adapter. With the data collected on each product, all data points are put into a separate Excel spreadsheet for comparative analysis.

A screenshot of the software PassMark's WirelessMon.

A hypothetical plot of four wireless AC USB adapters with the distance from the router expressed in feet (x-axis), and the signal strength in decibels (dB, y-axis). While the red and black lines follow a linear progression, the blue and green plots illustrate how nonlinear signal strength may be.