tinySA: Discover interference and goal antennas

Long-time readers know that I like to test compact and, if possible, inexpensive devices. I recently found another tool to add to my backpack when I’m back on the road.

Seven years ago when I wanted a spectrum analyzer to toss in my laptop bag, I spent about $ 500 (I don’t remember the exact price) on a 5 GHz spectrum analyzer that is slightly larger than a USB -Flash drive from Triarchy. The company still sells miniature USB spectrum analyzers that can cover frequencies up to 8.15 GHz. I am sure the analyzer and associated software have improved since I purchased my device.

A number of innovative, low-cost RF instruments have recently been introduced. The NanoVNA, which I’ve already written about, is one of them, and the basic design has been tweaked so that performance is now close to units that cost orders of magnitude more.

It seemed to me that with the right firmware, the NanoVNA could be turned into a spectrum analyzer. As far as I know, that didn’t happen, but I found the tinySA spectrum analyzer for about $ 50! Details can be found at www.tinysa.org/wiki.

The device is sometimes available in the US from R & L Electronics or directly in China from the Zeenko store on AliExpress. I ordered mine from another store I trusted on AliExpress and it took me a month to arrive. Half of that time was spent sending USPS mail after it arrived in the United States.

POSSIBLE PROBLEMS

Before you get too excited, like the early NanoVNA devices, this device has limitations. However, within its primary frequency range of 0.1 to 350 MHz and even the extended “high” range of 950 MHz, it is quite usable and offers some features that are not available in my older Triarchy analyzer. While it’s not much bigger than a USB ATSC tuner, it does contain a battery and a tiny 2.8-inch (diagonal) LCD touchscreen.

tinySA size compared to the USB tuner (Image credit: tinySA)

The tinySA-Low input for frequencies below 350 MHz has filtering and adjustable attenuation in steps of 1 dB between 0 dB and 31 dB. It contains a built-in level calibrator for this input and after calibration the specified accuracy is +/- 1 dB. With a resolution bandwidth of 30 kHz, signals down to –102 dBm can be recognized. The spore-free dynamic range is 70 dB at this resolution bandwidth. Frequency accuracy is specified as a selected resolution bandwidth, which can be set to 3, 10, 30, 100, 300 or 600 kHz or to “Auto”. Not bad for $ 50.

I know many, if not most of the readers will be interested in how it works with the “free” high input from 240 MHz to 950 MHz. The first thing you need to know is that this input is not filtered and is not attenuated internally. Filters and attenuators can be purchased from manufacturers of RF components such as mini circuits and added externally. While the input impedance of the low input is 50 ohms if an internal attenuation of 10 dB is added, the impedance of the high input varies without an external attenuator. The high input also does not work with the internal level calibrator, so an external reference is required for calibration.

Since there is 100 MHz of overlap between the low and high inputs, you can use the low input to measure a signal in the overlap band, then switch it to the high input and manually adjust the level calibration (at that frequency). Without the filtering, the high input is also exposed to images. The firmware includes an option to mask “mirror images” nearby. When I used it to look at DTV signals in the UHF TV band, I found that images are not a problem.

Fig. 1 shows a screenshot of the FM tape at my home. The third signal from the left (90.7 MHz) is from Maui, which is 94 miles away and has at least one obstacle. The four stronger signals come from a location with an obstacle only 2.4 miles away.

Fig. 1: tinySA FM tape display (Image credit: tinySA)

Figure 2 shows a scan of the UHF TV band. The signal from channel 36 (far right) is from a 213 watt ERP translator, 5.5 miles away and in sight. The tendency is due to the rolling of the Antra ATF-600 LTE filter. The signal from channel 28 is interesting because the transmitter location K28JV is in the opposite direction (in Hilo) and is blocked by the terrain. None of the other Hilo stations are visible in the diagram. Even with the tradeoffs in high input, performance isn’t bad.

The high input should work well with UHF, for example to detect interference in wireless microphones or to align TV antennas. However, adding a 10dB attenuator or two to the high input is probably a good idea if you are working in a strong signal environment. I didn’t get a chance to test the tinySA at a broadcast site like Mount Wilson. I’m afraid that the plastic housing will cause problems even with input mufflers. The tinySA Wiki warns of this in its “Limitations” section.

Fig. 2: tinySA UHF TV band display (Image credit: tinySA)

AVAILABLE SOFTWARE

The 320 x 240 pixel screen limits the measurement resolution, but early software is available for using the tinySA with a PC. The page also contains a link to a version of tinySA-Saver that is based on NanoVNA-Saver and runs on Linux or Mac OS. However, the instructions seem to be written for use with a NanoVNA, not a spectrum analyzer, and unfortunately most of the tinySA settings are not available in tinySA-Saver, at least what I was able to see in the version tested in early January. The tinySA app for Windows worked quite well and was used to take the screenshots for Figures 1 and 2. 1 and 2. The app can switch between low and high mode.

There is obviously a need for improvement here. In the FAQ section of the wiki, the designers state that more advanced (and expensive) units can be offered if there is enough interest in the $ 50 unit to warrant production. Given the size and cost of a signal meter for aiming a television antenna or a larger portable spectrum analyzer, spending $ 50 on a device that not only offers an amplitude display but also a spectrum display was an easy decision to fit in my pocket. I wouldn’t mind spending $ 150 on a device with a wider frequency range, a metal case, and maybe a 4-inch screen.

As always, I look forward to your comments and questions. Send me an email at dlung@transmitter.com. I try to reply to all emails promptly, but if I’m busy and the email gets buried, I might miss it. If you don’t get a response within a week, email me again.

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