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Yet another dongle – this time it’s a spectrum analyser! By JIM ROWE L IKE MOST TEST instruments, spectrum analysers have shrunk in cost and size in the last few years, thanks to accelerating solid-state technology. But when someone talks about a portable spectrum analyser, most of us think of an instrument maybe just a little larger than a portable DSO. A recent example of these advancements is the Gratten GA4063 analyser I reviewed in the November 2013 issue of SILICON CHIP (page 84), which measures 400 x 210 x 136mm and weighs a modest 7kg. That’s much smaller and lighter than the spectrum analysers of only 15 years ago and its price tag of below $8000 is also considerably lower. There’s also the RF Explorer reviewd by stan Swan in the May 2013 issue of SILICON CHIP. It covered the range from 240-960MHz. But the technology is still galloping on, at an ever increasing rate. Early in 2013, a small Canadian firm called Triarchy Technologies Corp released the first of a series of Mini Spectrum Analysers housed in a USB dongle measuring a mere 87 x 23 x 15mm – including a USB type-A plug at the 78  Silicon Chip Jim Rowe spotted this USB Mini Spectrum Analyser dongle on eBay and was so intrigued he purchased one. Despite its tiny size and low cost, it offers impressive performance over the frequency range from 1MHz right up to 5.35GHz – with a few limitations but not enough to stop it being very handy for many portable applications. output end and an SMA female connector at the input end. It weighs less than 20 grams. Despite this tiny size, the TSA5G35 analyser covers the frequency range from 1MHz right up to 5.35GHz and offers some impressive features, including sourcing all of its power from the PC, via the USB cable; no separate power supply or battery pack is required. That’s what we call portable! And buying it via eBay, the cost of the TSA5G35 is much lower than you’d expect: US$599.00 plus US$30.00 for handling and international shipping, which equates to about A$750.00 at the current exchange rate. That’s about 1/10th the cost of the next-cheapest fully self-contained spectrum analyser covering the same frequency range. By the way, the TSA5G35 comes in a small black cardboard case, with protective foam around it. There’s a matching 30dB fixed RF attenuator alongside it, with SMA connectors at both ends so it can be easily screwed onto the input of the TSA5G35 to extend its signal level range. There’s also a 1m long USB extension cable (type-A plug to type-A socket) so you don’t need to have the TSA5G35 plugged directly into the PC’s USB port. Main features Here’s a listing of the main technical features that the unit offers: (1)  Input levels up to +20dBm (100mW) with the basic TSA5G35, rising to +30dBm (1W) with the add-on fixed RF attenuator. (2)  Built-in digitally-controlled input attenuator with seven ranges, covering from 0dB to -60dB in 10dB steps. This attenuator is also used to set the analyser’s reference level. (3)  A noise floor which hovers around -110dBm (710nV at 50Ω) for most of the frequency range, creeping up to -105dBm at around 1.6GHz and then to -100dBm (2.2µV) at 4.5GHz and above. The rated noise floor figure is -115dBm, measured at 1.0GHz with 5MHz span and the reference level set to -60dBm (I checked this with the unit I purchased and obtained an average reading of very close to -119dBm). (4)  A choice of eight software selectable ranges when it comes to frequency span: 1-2-5-10-20-50-100-500MHz and 1000MHz, although there is a siliconchip.com.au Fig.1: the software control panel has a wide range of settings and allows you to set markers to read the frequency and level at various points in the spectrum. The four coloured tabs at top let you choose the Current, Average, Maximum & Density plot modes, or combinations of these. proviso in that the two widest spans can’t be used where they extend over the 850MHz point in either direction. That’s because the TSG5G35 actually covers its overall frequency span in two ranges: 1MHz - 850MHz and 850MHz - 5.35GHz. (5) Four different resolution bandwidths (RBW): 50kHz, 100kHz, 200kHz and 500kHz. These are automatically selected by the Triarchy software to give the clearest display for each span range. (6)  Minimum sweep time of two seconds (‘1x’), which can be extended by factors of 1.5x, 2x, 4x, 8x, 16x or 32x. (7)  Here’s a few more hardware-related specs: minimum frequency step for 1MHz span is 2kHz; frequency stability better than ±5ppm with software calibration (not explained as yet); reference level accuracy quoted as <3dB between 100MHz and 5.35GHz at the ‘top level’ of the internal step attenuator; reference level flatness is quoted as <2dB within 100MHz span, also at the ‘top level’, and display range linearity is quoted as <4dB at 1GHz. (8)  The Triarchy software has the capability of calculating and displaying siliconchip.com.au not just the ‘current’ scanning plot, but also the ‘average’, ‘maximum’ and ‘density’ plots as well if you wish. Any of these four plots can be enabled or disabled simply by clicking on their respective ‘tabs’ at the upper right of the display. The different plots are colour coded to allow them to be distinguished from each other. (9) Other features of the software include the ability to set a number of measurement markers on the plots/ waveforms; to set the software to make allowance for the external 30dB attenuator, any input cable loss or antenna gain; to allow the user to select any of five different options for displaying the reference level and amplitude plot ordinates – dBm (the default), dBµV, dBmV, dBµV/m or dBmV/m2; to allow the user to save not only ‘snapshots’ of the current plots for printing out, but also to ‘record’ the scan data to disc, for processing by other software. A User Manual for the TSA5G35 and its software can be downloaded as a PDF file from www.triarchytech. com.   However, note that the manual is currently still in draft form and as yet a bit sketchy in places. On the other hand, Triarchy already has a series of Application Notes available, all PDF files which can be downloaded from their website. These cover the testing of signals from Bluetooth, DECT, mobile phones, SRD and RFIDs, WiFi routers and Zigbee. Trying it out So far, I’ve tried out the TSA5G35 on a desktop PC running Windows XP/SP3 and a laptop running the 64-bit version of Windows 7. In both cases, the TSA5G35 and its software worked fine, the only difference being that things do slow down a bit on the Windows XP machine when you select the ‘density’ plot. However, Triarchy The Triarchy USB Mini Spectrum Analyser fits easily in the palm of the hand. Despite it’s tiny size, it covers the frequency range from 1MHz to 5.35GHz. February 2014  79 Fig.2: this spectrum plot shows the WiFi signals coming from the author’s network router. The yellow trace shows the most recent ‘current’ plot, while the magenta trace shows the maxima and the somewhat splodgy blue and cyan trace shows the density plot. Fig.3: the ‘current’ plot of a 1GHz signal from a Gratten GA1484B generator, with an output level of -90dBm (7.1μV) and using a direct connection. The signal peak is very close to -91dBm (possibly due to small losses in the connectors). warns that this option does involve a lot of processor ‘crunch power’ and so really needs a fast and powerful machine running 64-bit Windows 7. 80  Silicon Chip Overall, the device and its software are quite easy to drive in terms of making the majority of common spectrum analyser measurements. I also found that it met or exceeded its main performance specifications, although the user manual doesn’t explain (as yet) how to calibrate it in terms of frequency or amplitude level. While checking the TSA5G35’s noise floor over the full frequency range, I did find small spurious signal peaks at 48MHz and 96MHz. These seem likely to be from an oscillator inside the dongle but as they were both quite small (-99dBm and -101dBm), they don’t seem likely to cause any real problems in most applications. I also tried using the TSA5G35 to look at the WiFi signals coming from my network router, using a small ‘whip’ antenna from an old router connected to the input of the TSA5G35 as a near-field ‘sniffer’. The plots I obtained with this antenna (and the TSA5G35) spaced about 1.5m from the two antennas of the router are shown in Fig.2. To make things clearer, the yellow trace shows the most recent ‘current’ plot, while the magenta trace shows the maxima and the somewhat splodgy blue and cyan trace shows the density plot. As you can see, they show that most of the signals are centred on 2437MHz, which seems to be ‘channel 6’ in the WiFi band, with a smaller group of signals centred on 2457MHz (channel 10) and even fewer signals outside these two main groupings. Other tests I tried involved using the TSA5G35 to check the output of the Gratten GA1484B signal generator I reviewed in the November 2013 issue, with the generator set for different frequencies and output levels, and with either a direct connection between the two or via a 1m long RG-213 cable. In each case, I also had to use an N-type to SMA adaptor and, in some cases, an SMA gender changer as well. You can see the results of a couple of these tests in Fig.3 and Fig.4. Fig.3 shows the ‘current’ plot of the generator signal at 1GHz, with an output level of -90dBm (7.1µV) and with a ‘direct’ connection. Although I didn’t set a marker for the signal peak, it clearly shows a level of very close to -91dBm. I presume the 1dB difference is due mainly to losses in the two connector series adaptors but there may also be a small error in terms of the TSA5G35’s level calibration. Fig.4 shows the result of the same kind of test with the generator output siliconchip.com.au set to 3.9950GHz and an output level of -50dBm. As you can see, the peak level in this case is shown as -50.55dBm, suggesting a smaller loss in the series adaptors. On the other hand, the peak frequency is shown as 3995.04MHz, which suggests a small error in TSA­ 5G35’s frequency calibration. While not all that great, hopefully this can be reduced when I find out how to perform the ‘software calibration’ . . . Any complaints? Not really – just a few minor niggles, which can hopefully be sorted out by Triarchy Technology when they produce the final version of the TSA5G35 User Manual and also gradually improve the control software. For example, you can’t at present program a scan by specifying the start and stop frequencies; you can only do it by setting the centre frequency and the span. This can often require either a little mental arithmetic or a pocket calculator. It would be nice to be able to set a scan by specifying the start and stop frequencies, as an alternative. It also be good to have the ability to change the resolution bandwidth (RBW) manually and perhaps be able to achieve spans of less than 1MHz, eg, 100kHz. To summarise, the TSA5G35 USB Mini Spectrum Analyser seems to be a very capable little performer, particularly when you consider its remarkably attractive price. While its performance is clearly not up to the level provided by much more expensive self-contained analysers, my impression is that it provides most of the Fig.4: the result with the signal generator output set to 3.9950GHz and an output level of -50dBm. The peak level is now -50.55dBm, indicating a much smaller loss in the series connectors. The peak frequency indicated is 3995.04MHz, due probably to a small error in TSA5G35’s frequency calibration. capabilities needed for general purpose spectrum analysis. This would include checking cordless phones and wireless video links, mobile phones and 2-way radio gear, Bluetooth and WiFi gear, and so on. It should also be suitable for nearfield EMC testing out in the field. By the way, you don’t have to search around on eBay to find the Triarchy TSA5G35. All you need do is go to their own website at www.triarchytech.com, click on the [Products] button, select the TSA5G35 from the list of products and then click on the ‘To order from eBay click here’ link. If you do go to their website, you’ll find that they are now manufacturing three other USB dongle-based spectrum analysers as well. One, designated the TSA4G1, covers up to just 4.1GHz and is a little cheaper than the TSA5G35. Another, designated the TSA12G5, covers the frequency range from 4.9-13.5GHz and is more SC expensive. Full range of PICAXE products in stock now! PICAXE Chips, Starter Packs, Project Boards, Experimenter Kits, Books, Software and Accessories. PICAXE 2x16 and 4x20 OLED Displays OLED displays provide much brighter displays, better viewing angles and lower current consumption making them a great alternative to LCD’s. PICAXE Starter Packs available for 08M2, 14M2, 18M2, 20M2, 28X2 and 40X2 Microprocessors. This module allows PICAXE projects to display (yellow on black) text interfacing via one single serial line or I²C bus. PICAXE-18M2 chip is provided pre-programmed with the open-source AXE133 firmware. For pricing and to shop online, visit www.wiltronics.com.au Ph: (03) 5334 2513 | Email: sales<at>wiltronics.com.au siliconchip.com.au February 2014  81