Design Con 2015

Product tryout: iOS spectrum analyzer lights up with WiFi

-January 25, 2012

Oscium, the company that developed an iOS oscilloscope, has added a spectrum analyzer/power meter for WiFi
 WiPry iOS spectrum analyzer from Oscium
The WiPry Wifi spectrum analyzer/power meter connects to any iOS device.
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frequencies. The WiPry isn't a general-purpose spectrum analyzer because it's frequency range is limited to the wifi band: 2.4 GHz to 2.495 GHz. It's available as a spectrum analyzer only ($99.97), an RF power meter ($149.97), or a combination of both ($199.97), which was the unit I tried. See a video of the WiPry in action.

The WiPry's primary purpose is to help you troubleshoot interference on your wireless network from interference. It lets you see the signals on each of the 13 Wifi channels. I tested the WiPry at home, where my computer detected 11 wireless networks-and that's with my closest neighbor's wireless router turned off because the house is vacant during renovations.

Like its oscilloscope cousin, the WiPry attaches to its host directly through its I/O connector. While that's convenient, it feels kind of weak and could break unless you take care of the system. I'd rather have an extension cable. But wait, Apple's extension cable won't work because it extends the power only.

As a spectrum analyzer, the WiPry will show you the activity in the WiFi band. It offers two displays, a "real wave" and
Figure 1. In “Real Wave” mode, the WiPry shows peaks when a Wifi signal appears.

Figure 1. In "Real Wave" mode, the WiPry shows peaks when a Wifi signal appears.

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a waterfall. The real wave is just what you'd expect, peaks appear whenever a wireless devices transmits (Figure 1). But, those peak some in short bursts and are difficult to capture. Fortunately, the WiPry has a persistance feature that holds the peaks for a few seconds. The waterfall display lets you see the density of the signals as they scroll across the screen. But, the points are difficult to see in the default colors, but yo ucan change them to improve visibility (Figure 2). My home wireless router uses channel 6 and that's apparent from the waterfall display.

The WiPry screen lets you highlight any of the 13 wifi channels. Simply tap the "+" sign in the screen's upper left corner. That lets you see the bandwidth of each channel and how the channels overlap (Figure 3). You can also highlight any of the WiFi channels by touching any of the channel buttons (Figure 4) and then touch outside the highlighted channel to see another channel. The video demonstration lets you see that in action.

As with any spectrum analyzer, cursors can help you measure differences in waveforms. The WiPry has vertical and
 Figure 2. A waterfall display shows a history of WiFi signals.

Figure 2. A waterfall display shows a history of WiFi signals.

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horizontal cursors that let you measure frequency and amplitude difference among signals. The cursors can move individually or you can set them to track, meaning you just move one cursor and the other follows.

Digital instruments are great at capturing screens for reports. While you can do that by pressing the front button while holding the on/of button, you can also do that with the WiPry software. Just touch the settings icon and the screenshot button to capture the screen. I prefer using the WiPry's screen capture to the iPad buttons. The WiPry app produced a landscape image, which was easier to read than the portrait image that the iPad produced. You even use the WiPry app to send a e-mail containing the screen. That's useful when you don't have a USB cable or access to your computer.

As a power meter, the WiPry can capture bursts of received signals and display them as peak-to-peak, RMS, duty cycle, min, max, and several other measurements. Power
Figure 3. Touching the “+” button reveals WiFi channel frequency bands.

Figure 3. Touching the "+" button reveals WiFi channel frequency bands.

Click on image to enlarge

bursts appeared randomly and were difficult to capture at first. When they did appear, they would fade in a few seconds, making cursor measurements rather difficult. Touching and holding the pause/play button sets the WiPry for single-shot capture. Then, the image held.

Unless you're an RF engineer, using a spectrum analyzer can be intimidating. You also need a familiarity with the nature of WiFi signals to even begin to use this instrument. Unfortunately, the documentation doesn't explain that, which left me somewhat lost because I didn't know what to expect from the display. Instead, the manual simply tells you what will happen when you touch a screen button. I can figure that our without a manual. Oscium needs to add explanations to its documentation for engineers who may be new to measuring WiFi signals.

The WiPry not only displays spectrum and power measurements, it can record them. That's useful when you need to analyzer signals in detail offline. The WiPry
 Figure 4. Touching each frequency band highlights signals in the band.

Figure 4. Touching each frequency band highlights signals in the band.

Click on image to enlarge

saves data in csv format for easy importing to Excel.

The WiPry seems to have little effect on the iPad's battery life. I've left it on all day and still have sufficient power left.

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