Even if you don’t work regularly with transmitters, an RF spectrum analyzer can be quite handy in helping control RF interference. I wanted one when I was accumulating analog test gear in my early career and coveted the models from Tektronix and Hewlett-Packard that were far beyond my reach. Fortunately, hardware and software advances can now put a pocket-sized spectrum analyzer in your tool kit for under $100.
In the A/V world, practical uses for the tinySA include observing spectrum used by wireless audio gear like microphones, and by RF-based TV distribution systems (CATV). It can also be used to optimize over-the-air TV reception (yes, that’s still a thing). Since its range tops out at 960MHz it’s not usable for looking at Wifi.
The device itself is about the size of a pack of playing cards, with a couple SMB signal connectors, a USB-C for computer connection and charging, and a single multi-use control button. It also has a touchscreen, which works best if you have a small pointer. The built-in display is clear but quite small for taking a close look at signals. The free Windows app provides a large display and many other useful functions.
The tinySA has two frequency ranges, 0 – 350Mhz and 240MHz – 960Mhz, selected by the Mode menu. This menu presents four choices because the tinySA also has a signal generator that can operate in either range. The generator can be used for self-calibration of the low range or sending signals to other equipment.
When first powered on it loads the default Startup preset, which shows the full width of each range, so the display tends to look like a lot of random noise. Narrowing the range to a known band is helpful for getting your bearings. Set the Mode to the Low range (with antenna attached to the Low connector), set the center frequency to 100MHz and the span to 50MHz. Now you’re looking at 75MHz – 125MHz, which is a bit wider than the FM radio band. In most parts of the U.S. you’ll see a noisy baseline with a few large spikes, some of which are FM station carriers. If you narrow the span further and adjust the level scale you can “zoom in” on a few stations and identify them if you know their frequencies. The default preset has a marker that tracks the highest level, which at my house is Washington, DC music station “DC101” at 101.1MHz.
The Windows app makes it easy to control the tinySA and navigate around different settings and provides an excellent image. In my setup (running Windows 10 in a virtual machine on a Macbook) when I connect the USB-C cable it establishes a “serial-over USB” connection on COM3. Select this in the upper left of the software window and hit Connect. Once connected, click the >> Scan button and the live display will appear in a few seconds.
The main parameters are along the left side, including an area with “memory” buttons for saving and loading scan images (not presets). This allows you to overlay and compare scans. You can change the display frequency and level ranges by click-dragging at the edges of the graph, or option-click on the graph to get a contextual menu for setting markers and other functions. Most on-screen controls have hints that appear when you mouse over, which is a quick way to learn what’s what.
One handy function in the app is the ability to highlight different frequency bands on the display. This is turned on with a switch at the top of the window, and the choice of bands is selected in the Settings menu. The software comes with many defined bands, including radio, TV and HAM, or you can save your own. Also in Settings you can change colors and other visual aspects, and set the file path for storing captured scans.
I found that changing parameters stops the live scan, so you have to click >> again. And there can be some fussiness between the device and computer which requires disconnecting and reconnecting or restarting one or the other. Make sure the Mode setting matches where the antenna is attached! And be aware that some parameters, like Span and Points per Scan, interact in ways that might appear to be a fault but are actually normal. I found that 1000 points per scan on the computer display was a good compromise between detail and refresh time for my purposes.
Figure 1 above is an (annotated) image capture in northeast Washington, DC. The gray area between 470 and 610MHz is the UHF TV band. This was viewed using both Averaging and Max Hold functions to clearly show the 6MHz-wide “squared off” spectra of digital television stations in the U.S. There are also two wireless mic transmitters, one of which is right in the middle of a TV channel! This isn’t really a problem, since the mic is far stronger within the building, but not great planning by someone.
Figure 2 shows sixteen QAM (J.83B) CATV channels. Note that these are also 6MHz wide. The inset is the display on the tinySA itself, which you can also capture in the computer app.
The tinySA spectrum analyzer is not produced by a big manufacturer and has a “home brew” quality about it. The developer, Erik Kaashoek, started the project for fun and utility. He spends a lot of time maintaining it and the Windows software (along with other contributors). The online wiki has plenty of docs and videos, and there is an active user base for help. Interestingly, the tinySA is popular enough that there are cloned knockoffs, so the wiki has information on where to buy a legit unit and how to spot fakes.
When it comes to RF audio gear, the tinySA spectrum analyzer does not replace the sophisticated monitoring and frequency calculations provided by manufacturers (particularly when many transmitters are involved) but being able to visualize the RF environment, and what the equipment is doing, is great for troubleshooting and increasing confidence. If you want to keep an eye on RF activity, or learn about it, you should find the tinySA quite useful and an amazing value! And if you’re really into RF, check out Doug Lung’s regular column in SVC sister publication TV Technology, which is where I originally learned about the tinySA.