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TEKWAY DST1102B WI Review by JIM ROWE A little over 17 years ago, I realised that if I wanted to continue designing electronics equipment, I needed to upgrade from my flaky old analog scope to a digital storage scope or ‘DSO’. So I took a deep breath and invested in a shiny new 100MHz 2-channel DSO from Tektronix (the TDS320). It cost around $4500 if I recall, which seemed like a massive sum; but it also seemed to offer pretty well all the features I’d need for some time to come. And this indeed proved to be the case, as the trusty TDS320 served me faultlessly until a few weeks ago. But then its traces flew out of sight, off the top of the screen and couldn’t be persuaded to come back. The front panel board had developed a fault and I found that replacement boards were no longer available. My only options were to send the scope back to Tek in the USA together with a cheque for US$1550 to cover a ‘best efforts only’ repair, or to use the TDS320 carcase as a trade-in on a new DSO. Since sending the 7kg TDS320 back to Beaverton in Oregon would probably cost about $400-500 anyway, with no guarantee that they would fix it, the decision was easy – it was clearly time to upgrade to a new DSO. So I began searching the web, to see what might now be available in my price range. And straight away I started to 16  Silicon Chip realise just how far DSOs had come since I had invested in the now-ancient TDS320. Just about all of the latest models offered full colour LCD displays, for example, instead of the hefty 7” monochrome CRT monitor I had become used to. This made them dramatically smaller and lighter in weight, while at the same time making the display much clearer and easier to analyse. There had also been a significant increase in sampling rates and an even more dramatic increase in sample memory depth. Many of the latest models offered real-time sampling up to 1GS/s with a memory depth of well over 10KS (kilosamples) and in some cases up to 500KS or 1MS – a big advance on the 500MS/s sampling rate and modest 1KS memory depth per channel offered by my old DSO. Most of the new models also offered a wider range of automatic measurement functions, including FFT frequency analysis, plus a more comprehensive range of triggering options. Just about all of them also offered the ability to save waveform screens and setups in either internal memory or a plug-in USB flash drive – or both. Yet at the same time, the price tags on all of these latest models had dropped dramatically from the $4500 I had paid for the old TDS320. Some of the 2-channel 100MHz models were down to below $1000, in fact. siliconchip.com.au Digital storage ’scope technology has pushed ahead in leaps and bounds over the last few years. Each new model offers higher sampling rates, wider bandwidth, deeper sample memory plus a full colour display growing in both resolution and screen size – combined with shrinking physical size and a lower price tag than previous models. Here’s a look at the DST1102B from Chinese firm Tekway, showing just how far DSOs have come to date. It offers an impressive array of features, for a price that simply blows away most of the competition. DESCREEN 100MHz DSO So I was faced with picking my way through a bewildering array of models offering all kinds of fancy bells and whistles, with prices ranging between about $1000 and $2500. If you’ve been looking for a new DSO you’ll know exactly what I mean. These two shots give a good idea of the width and depth (or more accurately, the lack thereof!) of the DST1102B. The rear panel is pretty spartan, with just the power input and that second USB port. siliconchip.com.au January 2011  17 The leading edge of a 125kHz square wave from the Novatech scope calibration source, which has a very fast rise/ fall time of 500ps (picoseconds). This shows the risetime of the DST1102B itself to be 3.300ns, which corresponds to a bandwidth of 106MHz – just over the rated 100MHz. An FFT frequency domain display of a 100.350kHz sinewave from a reasonably low distortion AF generator, with the fundamental peak visible at the left-hand end. All harmonics are at least 20dB below the fundamental up to above 23MHz. Now I’ll cut to the chase by telling you that after quite a bit of downloading and comparing specs, I finally settled on the new DST1102B scope made by Tekway Technologies in its factory in Hangzhou, China. (As an aside, you won’t be surprised to learn that most of the latest DSOs seem to be made in China.) Tekway scopes are distributed in Australia by Trio Smartcal, which you’ll find at www.triosmartcal.com.au In a sense then, this review of the DST1102B is also an explanation of the rationale which led me to choose it over the other 2-channel 100MHz DSOs currently available. I’m being quite up-front about this, in the hope that my comments might help other people trying to pick the right brand and model for themselves. OK then, away we go. The first thing that attracted me to the Tekway DST1102B was its widescreen hi-res colour display. The screen measures 177mm (7”) diagonally, which is over 20% larger than the 145mm (5.7”) screen found on most other models. At the same time it has much higher resolution – 800 x 480 pixels, compared with the modest 340 x 240 pixel ‘quarter VGA’ resolution offered by most others (even those from the ‘big names’). So the display is not only bigger and wider than most others, it’s also much sharper and more detailed as well. Of course there’s much more to it than that. For example the sampling rate extends up to 1GS/s for real-time sampling and up to 25GS/s for equivalent time sampling – most impressive. And the memory record depth extends up to a whopping 1MS for one channel, or 512KS per channel when both channels are being used. What’s the advantage of this very deep sample memory? In a nutshell, it allows you to ‘zoom in’ to any particular point in a sample record and examine it in detail. The DST1102B in fact provides a ‘zoom’ function which allows you to do just that, with the original waveform shown in the upper screen window and the zoomed-in area in the lower window. You can see this quite clearly in the screen grabs below. Another nice feature of the DST1102B is that it can update the acquired waveforms at up to 2000 times per second, which is 4-5 times faster than most of the competing models. This gives a very lively ‘real time’ display but with no trade-off in terms of display brightness (as found on some of the other LCD-based models). In addition it offers a ‘selectable persistence’ display option, which gives you a choice of ten different wave- This next screen grab shows the DST1102B triggering on line 118 of the composite PAL video signal from a DVD player, with the basic two-line waveform shown at the top plus a zoomed-in view of the centre horizontal sync pulse and colour burst below. All details are clearly visible. The same video signal but this time with the scope set to trigger on line 8 of the waveform – ie, in the vertical blanking interval (VBI). In the lower ‘zoomed in’ window is the first two of the six ‘dancing pulses’ added to lines in the VBI as part of the Macrovision copy protection system. The important features 18  Silicon Chip siliconchip.com.au In the top window is a 101.720kHz triangular waveform signal from a function generator, plus an FFT of the same signal in the lower window. Note that as well as the 101kHz fundamental peak near the left-hand end of the display, both odd and even harmonics are visible up to the 7th. Another FFT of the triangular wave signal from the same function generator, at a frequency of 214.710kHz, expanded horizontally to make the lower-order harmonics a little clearer. The 2nd harmonic is about 17dB down, the 3rd about 9.5dB down and the 5th harmonic about 15dB down. form display durations: Automatic (ie, no persistence), 0.2s/0.4s/0.8s/1s/2s/4s/8s or infinite. As well as the ‘Auto Set’ or automatic setup mode now found on most new DSOs, the DST1102B also offers an internal self-calibration mode which can be selected from its Utility menu at the touch of a button. There’s also a built-in real time clock and calendar, whose time and date are displayed on many of the measurement screens – and can be saved and exported in screen grabs, as you can see from at least one of the grabs shown here. When it comes to acquisition modes and triggering options the DST1102B offers pretty well everything found on even the most expensive models. For example it can acquire waveforms in one of four modes: real-time sampling, peak detect or averaging (with a choice of 4, 16, 64 or 128 waveforms), plus equivalenttime sampling. The acquisition memory depth can also be set to either 4KS, 16KS, 40KS or 512KS/1MS, as you wish. There are six selectable triggering modes, too: • Edge (rising or falling); • Pulse Width (20ns – 10s, with positive or negative width and also a choice of <, >, = or =/ to a reference pulse width); • Video (NTSC, PAL or SECAM, field select or line select (line 1 – line 525 for NTSC, 1 – 625 for PAL/SECAM); • Slope (trigger on a positive or negative slope, </>/=/=/ to a set time span of 20ns-10s); • Overtime (i.e., delayed triggering, where triggering is delayed by a nominated time duration from a positive or negative edge and the delay time can be set between 20ns and 10s); and • Alternate, or Swap Trigger (where the scope triggers from each channel alternately, with a different triggering mode and/or sweep frequency for each). I should mention that the triggering system also provides a holdoff facility, where the scope can be prevented from triggering again for a nominated time after each triggering. This is great for capturing individual bytes or words in a serial stream. It also offers a choice of HF reject, LF reject and noise rejection filters, to optimise triggering reliability. There’s also an impressive range of automatic waveform measurements, any of which can be applied to either channel: frequency (6-digit resolution), period, arithmetic mean voltage, peak-to-peak voltage, cycle RMS, minimum, maximum, rise time, fall time, positive width and negative width. Up to eight of these measurements can be taken and displayed on-screen at any time. Quite apart from these ‘automatic’ measurements there’s also the ability to make ‘manual’ measurements between pairs of voltage or time cursors and even the ability to ‘trace’ the time and voltage values at any desired point on A composite PAL signal from a DVD player, showing the ‘dancing’ Macrovision pulses on lines 8 and 9 in the VBI. The pulses here are a little higher than those shown on the previous page and there are now seven pulses in line 8 but only six in line 9. An unmodulated 100.016MHz sinewave from an RF signal generator illustrating the ability of the DSO to hide the measurement menu (right-hand side of the screen), so a waveform can be displayed over the full screen width. A single button press redisplays the menu at any time. siliconchip.com.au January 2011  19 This shows one of the DST1102B’s many clever triggering features: the ability to trigger alternately from the signals on channel 1 (a 100.0kHz signal [yellow]) and channel 2 (a 145.6kHz squarish wave [blue] from a different source). Both are rock steady, as a result of the alternate triggering. An illustration of the way the DSO’s measurement cursors can be used to make more specialised measurements. Here is the ringing after the trailing edge of 350ns-wide pulses, with the cursors used to show that the ringing lasts for around 210ns (delta T) and has a frequency of 4.76MHz. a waveform using a single time cursor. While we’re talking about measurements and their display, it’s worth noting that although the DST1102B displays many of the measurements in the ‘menu’ column at the right-hand side of the screen, this column can be ‘hidden’ at any time simply by pressing a front panel button. This makes the full screen width available for examining the waveform(s), if you need it. Pressing the same button again restores the menu column and any measurements displayed on it. Naturally, the DST1102B does provide the usual waveform ‘math’ functions: CH1 + CH2, CH1 - CH2, CH2 - CH1 and of course FFT (Fast Fourier Transform). In the FFT mode there’s a choice of Hanning, Flattop or Rectangular window functions, and there’s also an FFT Zoom button to set the horizontal magnification in the FFT display window (x1, x2, x5 or x10). Cursors can also be used to make two measurements within the FFT spectrum: amplitude in dB (relative to 1V) and frequency in Hz. in the current version. Luckily these bugs were fixed soon after and I was able to get the scope and the PC “talking to each other” quite nicely. Two USB ports Like many of the latest DSOs the DST1102B provides a ‘Host’ USB port on the front panel, so that waveforms and setups can be saved to a standard USB flash drive or ‘thumb drive’. (The screen grabs shown in this review were exported this way.) The same port can also be used to update the scope’s internal firmware, using files downloaded from the Tekway website and copied over to a USB flash drive. It’s then simply a matter of plugging the flash drive into the front USB port, selecting the scope’s ‘Utility’ menu and then pressing the ‘Software Upgrade’ and ‘Confirm’ (F6) buttons. There’s also a USB ‘Device’ port on the rear of the scope, to allow it to be hooked up to a PC directly using a standard USB A-B cable. Then by running matching software called ‘TTScope’ on the PC, display screens and setups can be transferred between the two in either direction, while the scope can even be ‘driven’ via a virtual front panel on the PC screen. The TTScope software can be downloaded at no cost from the Tekway website (www.tekwayins.net), although when I tried doing this there still seemed to be a few minor bugs 20  Silicon Chip Summarising There are a few features of the DST1102B that I haven’t mentioned as yet – like the inbuilt Help system, which provides context relevant on-screen help at any time simply by pressing the Help button. This largely makes it unnecessary to refer to the manual, which comes as a pdf file on a CD supplied with the scope. The vertical and horizontal position controls also have a handy ‘press to centre’ option, while the horizontal timebase control has a similar function to allow adjustment of the horizontal zoom magnification. Like most of the latest DSOs the DST1102B also provides a 1kHz squarewave signal output on the front panel (at lower right), to make it easy to adjust probe compensation. And the DST1102B comes with two high quality x10/x1 passive probes, with a bandwidth of 100MHz in the x10 switch position and 6MHz in the x1 position. So that’s the basic rundown regarding what you get with the Tekway DST1102B scope. As you can see from the main photo it comes in a sturdy case, with a built-in carrying handle and swing-down tilting feet. The case measures only 313 x 142 x 108mm (W x H x D), and weighs in at a mere 2.08kg – less than one third the weight of my old TDS320. As you can see then, the DST1102B compares very well indeed with virtually all of the latest-tech DSOs on the market, and blows many of them right out of the water. So what would you expect to pay for this compact high performance instrument? I’ll tell you: at the time of writing this review, Trio Smartcal have it available for $1495 plus GST. This is about half the price you’d expect to pay for a big brand model with comparable specs, so you can see why I decided to go with this one. More info? If you would like more information on the Tekway DST1102B, you’ll find it on the Trio Smartcal website at www.triosmartcal.com.au Or you can call them on 1300 853 407. SC siliconchip.com.au