WifiMETRIX is a new type of diagnostic tool that uses a dual-band 802.11 (i.e. Wi-Fi) chip to monitor and troubleshoot Wi-Fi networks. It implements two important features — AirHORN and WifiPROBE. The built-in Wi-Fi chip can perform both signal generation (AirHORN) and throughput diagnostics (WifiPROBE) on each channel.
The AirHORN function is an RF signal / channel generator that transmits stable and accurate RF signals for each of the Wi-Fi channels, and aids in testing Wi-Fi antennas, RF shields and wireless networks.
The WifiPROBE function traverses each channel and measures the available transmit time. When the goal is to choose the best channel — the one with the highest available throughput — then WifiPROBE is the tool of choice.
WifiMETRIX operates in stand-alone mode and does not need to associate with an access point in order to perform its functions. It is a truly unique device that is tailored for troubleshooting Wi-Fi problems and computing the best channel.
WifiMETRIX has been designed to be intuitive and easy to use — no need to study large user manuals. The best way to become familiar with the device and its capabilities is by experimenting — so, power it on and give it a go. Also, we suggest reviewing our short FAQ page, which may help explain some principle concepts about monitoring and troubleshooting 802.11 (Wi-Fi) networks.
The following are the main hardware features of WifiMETRIX (the following section describes more about functional features).
- Handheld device with dual-band 802.11 Wi-Fi chip
- Solid aluminum case plus silicon rubber boot protector
- Standard 50 ohm SMA antenna connector
- 128×64 built-in LCD screen
- Includes dual-band antenna for 2.4x and 5.x GHz ISM bands
- Includes micro-USB cable for recharging
- Includes 50 ohm SMA terminator to protect antenna connection
- SMA terminator (dummy load) also used for calibrating the device
By far the most important feature on this list is the dual-band, 802.11 chip — no other tool uses an 802.11 chip to perform Wi-Fi diagnostics. This is a huge advantage because it frees the user from having to interpret RF data or metrics. Instead, WifiMETRIX’s 802.11 chip reports what it thinks about the health of each channel. WifiMETRIX uses a metric based on IMMI — a patented technology based on the available transmission time of each channel. You can read more about IMMI here.
The unit includes a 50 ohm impedance RF connector (standard female SMA format). This is used for attaching the dual-band antenna that we include with the device. Feel free to substitute your own antenna — the only constraints are you adhere to the 50 ohm requirement and your antenna includes a standard male SMA connector.
When a compatible micro-USB cable is connected then the unit will begin charging (regardless of the position of the power switch). With the micro-USB cable attached then the device’s power will come from that USB connection. When the micro-USB cable is not attached, then the device draws power from its internal, lithium battery.
Assuming the device is powered-off it will take approximately 3 hours to fully recharge. This is based on the chip manufacturer’s specification. The discharge time for the battery depends on how the device is being used. When running in AirHORN mode and transmitting at full power, the device will run for about 2 hours. When sitting idle (but powered-on) the device will fully discharge in about 5 hours. When the device is stored and not being used, the internal battery should hold its charge for a few months.
When storing or transporting the unit we recommend attaching the 50 ohm SMA terminator (included) to protect internal components from strong electric fields.
WifiMETRIX uses the LCD screen and keyboard to access menus and features. It’s really pretty simple to use, though we’ve summarized a few of the menus below. In general, you would use the UP / DOWN arrow keys to highlight a menu option and then press the ENTER key to move to the next screen. You can always return to the top-level main menu by pressing the MENU key.
When the device is powered-on it will display the main menu. Use the UP / DOWN arrow keys to highlight an option and then press the ENTER key to move to the next screen. You can always return to this top-level menu by pressing the MENU key.
This is the primary menu for AirHORN. Here you can select which Wi-Fi band to use, output power and which AirHORN mode to use.
This is the primary menu for WifiPROBE. Here you can select which Wi-Fi band to use, and which WifiPROBE mode to use.
Below is a list of “short-cut” keys. However, due to the small keyboard, please be aware that certain key-presses behave differently depending on the context menu. Feel free to experiment a bit and familiarize yourself with the keyboard’s layout.
Return to the main menu — i.e. OPERATIONAL MODE
Depending on the context, used to select highlighted menu option or toggle between ACTIVE and PAUSED.
Depending on the context, used to toggle between 2.4x and 5x GHz bands or return to previous menu.
|[UP] and [DOWN] Keys||
Depending on the context, used to cycle through power output.
|[LEFT] and [RIGHT] Keys||
Depending on the context, used to cycle through channels.
WifiMETRIX features two “operational” modes — AirHORN and WifiPROBE. In AirHORN mode the device is used as an RF channel / signal generator. Using 802.11 packet injection, AirHORN transmits stable and accurate RF signals for each of the 802.11 (Wi-Fi) channels. In WifiPROBE mode the device provides unprecedented visibility into the performance of a wireless network. The information collected and displayed helps to simplify troubleshooting of interference-related problems and predicts the throughput performance of each 802.11 channel.
AirHORN Mode (Channel / Signal Generator)
When the device is powered-on it will display the main menu. Use the UP / DOWN arrow keys to highlight the ‘AirHORN’ option and then press the ENTER key to move to the next screen.
This is the primary menu for AirHORN. Here you can select which Wi-Fi band to use, output power and which AirHORN mode to use. To change which Wi-Fi band to use, use the UP / DOWN arrow keys to select ‘WiFi Band’ and press the ENTER key to toggle between the 2.4x GHz and 5x GHz ISM bands. To change the output power, select ‘Power’ and press the ENTER key to cycle through available power outputs — 2 dBm through 18 dBm.
Also, in AirHORN mode there a 3 available ‘transmit’ modes — ‘Single’, ‘Traverse’ and ‘Pulse’ modes. Select one of the transmit modes and press the ENTER key.
Here is an example of using ‘Single’ mode — where you can select a channel in either the 2.4x or 5x GHz band and achieve close to 100% duty cycle on that channel (at the normal 22 MHz-wide channel width). When using the 2.4x GHz radio module you can choose from Wi-Fi channels 1 – 13. When using the 5x GHz radio module you can choose from Wi-Fi channels 36, 40, 44, 48, 52, 56, 60, 64, 149, 153, 157, 161, 165. There is also a TX mode option — the radio can transmit either 802.11 packets or raw RF energy. When transmitting packets, 802.11g is used by the 2.4x radio module and 802.11a is used by the 5x radio module. After specifying the channel and TX mode select NEXT and press ENTER.
The next screen shows AirHORN in Single mode, using the channel 6 in the 2.4x GHz band and the power output set at 11 dBm. Pressing the ENTER key toggles transmission between PAUSED and ACTIVE. In the image below you can see that AirHORN is transmitting on channel 6.
Here is an example of using ‘Traverse’ mode — where you can automatically scan through the set of 2.4x GHz or 5x GHz channels. When using the 2.4x GHz radio module this mode will automatically traverse channels 1 – 13. When using the 5x GHz radio module this mode with automatically traverse Wi-Fi channels 36, 40, 44, 48, 52, 56, 60, 64, 149, 153, 157, 161, 165. There is also a ‘Speed’ option — when ‘Slow’ is selected then AirHORN will transmit for 30 seconds before moving on to the next channel. When ‘Fast’ is selected then AirHORN will transmit for 5 seconds before moving on to the next channel. After specifying the ‘Speed’ NEXT and press ENTER. As with Single mode, the next screen displays the current band, channel and output power. Pressing the ENTER key toggles transmission between PAUSED and ACTIVE.
Here is an example of using ‘Pulse’ mode — where you “burst” on a specific channel, and then ‘off’ for a set interval. Here the options are channel, burst duration (in seconds) and ‘off’ interval (in seconds). As with the other AirHORN modes, the next screen displays the current band, channel and output power. Pressing the ENTER key toggles transmission between PAUSED and ACTIVE.
WifiPROBE Mode (Channel Analyzer)
When the device is powered-on it will display the main menu. Use the UP / DOWN arrow keys to highlight the ‘WifiPROBE’ option and then press the ENTER key to move to the next screen.
This is the primary menu for WifiPROBE. Here you can select which Wi-Fi band to use and how the channel analysis results will be displayed. To change which Wi-Fi band to use, use the UP / DOWN arrow keys to select ‘Band’ and press the ENTER key to toggle between the 2.4x GHz and 5x GHz ISM bands.
In WifiPROBE mode there a 3 ways the channel analysis results can be displayed — ‘Traverse Channel Bars’, ‘Traverse Channel Table’ and ‘Selected Channels’. Select one of the analysis modes and press the ENTER key.
Traverse Channel Bars
Here is an example of using ‘Traverse Channel Bars’ — pressing the ENTER key toggles scanning between PAUSED and ACTIVE.. When using the 2.4x GHz radio module then WifiPROBE will traverse Wi-Fi channels 1 – 13. When using the 5x GHz radio module WifiPROBE will traverse Wi-Fi channels 36, 40, 44, 48, 52, 56, 60, 64, 149, 153, 157, 161, 165. As scanning occurs, WifiPROBE will compute the metric “% Available TX Time” for each channel. The higher the percentage the “healthier” the channel.
Pressing the ENTER key toggles transmission between PAUSED and ACTIVE. In the image below you can see that a narrow peak of RF interference at 2415 MHz blocks channels 1, 2, 3 — that is, causing their “% Available TX Time” to drop to 0%.
Traverse Channel Table
Here is an example of using ‘Traverse Channel Table’. This is similar to ‘Traverse Channel Bars’ above, except the results are presented in the form of a table (as compared to a bar graph).
Here is an example of using ‘Selected Channels’. This mode differs from ‘Traverse Channel Bars’ and ‘Traverse Channel Table’ in that you specify which channels to traverse. It takes approximately 2 seconds to compute the “% Available TX Time” metric for each channel — i.e. close to 30 seconds to scan an entire band. But suppose you are really only interested in channels 1, 6, 11 — then specifying only these 3 channels can significantly shorten the refresh time between scans.
AirHORN Single Mode — Two TX Modes:
WifiPROBE — Detecting Different Types of Interferers: RAW, ACI (Adjacent Channel Interference), CCC (Co-Channel Congestion)
WifiPROBE — Bar Decorations:
When operating in AirHORN mode, WifiMETRIX uses its 802.11 chip to promiscuously transmit without having to first associate with an access point. Furthermore, when transmitting in Single mode, the transmission can be in the form of 802.11 packets or RAW energy (a modulated, continuous, 22 MHz-wide channel shape). When transmitting in Traverse and Pulse modes, the transmission is always in the form of 802.11 packets. Below we show examples of what the Single, Traverse and Pulse mode transmissions look like when monitored by an RF spectrum analyzer.
The above image shows AirHORN transmitting in Single Mode where ‘TX Mode’ is PACKETS.
The above image shows AirHORN transmitting in Single Mode where ‘TX Mode’ is RAW.
The above image shows AirHORN transmitting in Traverse Mode.
The above image shows AirHORN transmitting in Pulse Mode — where Duration is 5 seconds, and Interval is 10 seconds.
The WifiPROBE function traverses each channel, measuring its available transmit (TX) time. This is reported as ‘% Available TX’, compared to a baseline reference. This metric — % Available TX — is a measure of a channel’s “health”. The higher this value then the more bandwidth is available for transmitting data packets. Using this metric, WifiPROBE can be used to rank channels from best-to-worst. However, a few more points should be clarified:
- Should you always use the channel with the highest ‘% Available TX’? For example, suppose your 802.11N channel has a theoretical bandwidth of 100 Mbps, but because of interference and congestion that has decreased to 40 Mbps — i.e. the ‘%
Available TX’ is 40%. Should you avoid using that channel at all costs? The answer is ‘not necessarily’. If your current bandwidth needs are only 5 Mbps — which is much less than the available 40 Mbps — then it is perfectly fine to continue using that channel because it still has plenty of capacity to handle your current traffic load. Only when your traffic load begins to approach the bandwidth ceiling is it then necessary to consider a different channel. WifiPROBE can tell you what that ceiling is, but it does not tell you the current traffic load.
- When monitoring the 2.4x GHz band you should always choose either channel 1, 6, or 11 — even if other channels have a higher ‘% Available TX’ value. There are few exceptions to this rule — and here’s why…
The image above shows the results of WifiPROBE scanning all the 2.4x GHz channels in a typical office environment. As WifiPROBE cycles through all the channels, the channel currently being measured is filled-in (e.g. channel 2 in this example). We see that some channels are higher than others — but all are greater than 50%. Since this is the 2.4x GHz band, we really should focus just on channels 1, 6, and 11. We would interpret this result to mean it is okay to use channels 1, 6, 11 for your AP.
In the image above we’ve used another WifiMETRIX in AirHORN mode transmitting on channel 6. As you can see, the AirHORN transmission significantly affects channel 6, along with adjacent channels. In this scenario or similar ones, it would then be best to use either channel 1 or 11.
In the image above we’ve again used another WifiMETRIX in AirHORN mode transmitting on channel 6. In this table view you can again see that channel 6 and adjacent channels are severely affected. Furthermore, the ‘CCC’ and ‘ACI’ tags give you a clue that the problem is caused by an 802.11 device (i.e. AirHORN). If we didn’t see those tags, then the problem probably is caused by a non-802.11 device.
In the image above we’ve again used another WifiMETRIX in AirHORN mode transmitting on channel 6. In this Selected Channels view you can again see that channel 6 is severely affected by the congestion caused by AirHORN transmitting on channel 6.
In the image above we’ve used an RF signal generator, transmitting at frequency 2440 MHz, which is near the center of channel 6 (2437 MHz). As you can see, even though this is a very narrow band interferer, it affects not only channel 6 but also neighboring channels.
The metric that WifiPROBE uses to compute the best channel requires that ‘% Available TX’ be compared against a baseline reference measurement for each channel. This baseline represents 100% Available TX — that is, no RF interference (or, as close as possible). To achieve this we’ve included a 50 ohm SMA terminator to be attached to the antenna connector. Furthermore, if you have a microwave oven available, we recommend placing the unit in the microwave oven during the duration of the calibration procedure (approximately 1 minute). And, of course, DO NOT use the microwave oven during this period. The microwave oven serves as a “poor man’s” Faraday cage. The combination of using the SMA terminator plus microwave oven closely approximates an RF environment with no RF interference — which will define our baseline of 100% Available TX. During the calibration procedure the unit will traverse all the 2.4x and 5x GHz Wi-Fi channels and record a baseline value for each channel. When you later use the device for WifiPROBE channel analysis, the value it measures will be compared to the corresponding baseline value and the ‘% Available TX’ can then be computed and displayed on the screen.
The calibration feature can be accessed by selecting ‘Configuration’ from the main menu, followed by ‘Re-calibrate’ in the CONFIG MENU.
For the next step, the menu reminds you to ATTACH THE 50-OHM SMA TERMINATOR (“DUMMY LOAD”). Also, if you have a microwave oven available, we suggest you place the unit in the microwave oven during the duration of the calibration procedure (approximately 1 minute). The goal of the calibration step is to approximate 100% Available TX time, and the combination of dummy load plus microwave oven serves as a “poor man’s” Faraday cage.
Once you press the UP key there is a delay of 5 seconds before the calibration process begins. This allows a few seconds to place the device in a microwave oven before the calibration procedure begins traversing channels and recording their baseline reference values.
Once calibration has completed, remember to replace the SMA terminator with the dual-band antenna.
From time-to-time we make available updates to the firmware that runs on your WifiMETRIX device. However, before updating, please make sure the version you will be updating to is more recent than the one currently running on your device. To check the current firmware version, select ‘About’ from the main menu (see image below).
The latest available firmware version is: 1.05
If your current version is older than the latest release, then it is okay to proceed with the update.
To upgrade the firmware running on your WifiMETRIX device from a Windows OS, you will need the following:
- The “WifiMETRIX Firmware Update Loader” tool, which can be downloaded from here: WifiMETRIX Firmware Update Loader
- The latest firmware file (*.bin) that will be used for the update — available here: Firmware Binary File
- Your WifiMETRIX device and a micro-USB cable. As a general rule, please use a quality USB cable (e.g. the one that shipped with the device) and attach it directly to the PC (and not through a USB hub).
- A compatible PC, running Windows 7 or higher.
Please follow the step-by-step guide below to update to the latest firmware version that you just downloaded.
1. Using the updater tool, load the latest firmware version that you just downloaded and press the ‘Load’ button.
2. Select the second CheckBox that begins: “If you have a WifiMetrix Unit running…”.
3. Select the third CheckBox that begins: “In WifiMetrix press buttons…”.
4. With the power switch in the OFF position, use the micro-USB cable to attach the device to your Windows PC.
5. This is the important step — press and hold the [LEFT] and [RIGHT] arrow keys, and at the same time switch the power ON. You should see the screen below:
6. On the updater tool, press the ‘Connect’ button. A dialog box show appear that confirms the connection. Read the message and confirm you are updating a WifiMETRIX device. This is important because a similar updater tool is used to update RF Explorer devices. Click the button that says ‘Device OK. Click to Upgrade’.
7. Using WifiMETRIX’s keyboard, press the [UP] arrow key to begin the update. You should see the message “Writing block” and the block numbers increasing.
8. When the update is done you will briefly see a screen that reports the update is ‘Done’ and the device is resetting.
9. And finally, after updating the firmware and resetting the device, it is necessary to run the calibration procedure again.
Performing the calibration is a simple process — here is the link:
There is a hidden diagnostic screen that is only accessible using a special key combination. We suggest you ignore this for now. However, in the event you need to contact our technical support, they may request this additional information. So, we present the procedure here. Just to be clear, in case you are curious there is no harm in accessing this hidden screen, but the results are intended solely for the technical support team.
To enable the diagnostics screen, power ‘on’ the unit and while the splash screen displays then press and hold the RIGHT arrow key. When powered ‘on’ this way a new ‘Diagnostics’ menu option appears at the bottom of the screen.
While in Diagnostics mode, the following short-cut keys are in effect:
This product would not be possible without the SeeedStudio Team who manufactures and tests WifiMETRIX devices.
The WifiMETRIX device is a reality due to the engineering excellence of Ariel Rocholl and his team in Spain. As with the development of most products of this complexity, there were many pitfalls and unexpected technical hurdles that we encountered along the way. We are especially indebted to Mr. Rocholl — there is no finer engineer on this planet.
WifiMETRIX is a Test and Measurement device, compatible with US FCC regulation 47 CFR Part 15.103(c).
WifiMETRIX is certified for CE compliance under regulations EN/IEC61236 and EN/IEC61000.
WifiMETRIX’s embedded firmware is copyrighted © by Ariel Rocholl, 2010-2017.
WifiMETRIX and WifiPROBE are registered trademarks in the USA and all EU Countries.