SDS2204 + MSO review
HW: 5-3
SW: 1.1.1.35.1
Reason for buyingI wanted to get a more modern oscilloscope to replace my Tektronix TDS744A (4 channels/ 500MHz) but it didn't need to be a 500MHz oscilloscope. Before last year the only option was to spend >€5000 on a Tektronix or Agilent with 4 channels. Then came the Rigol 1000Z series with 4 channels and not much later the SDS2000 series from Siglent offering a higher samplerate and a bigger screen compared to the Rigol 1000Z. Having digital channels could be useful as well. I do have a high end Tektronix logic analyser but it is heavy and the software is quite slow to use. Being able to offload some of the simple logic analyses tasks to an oscilloscope maybe worth while especially if it can do protocol decoding. The specifications for the MSO probe on the SDS2000 are not stellar though. The input capacitance of 10pf is rather high. Not problematic but I wouldn't use it for circuits going over 50MHz. IMHO 8 channels are just right. Having more is just overcrowding the screen especially if you also want to look at a couple of analog signals as well. I have used Agilent MSOs in the past and enabling 16 channels was a bit beyond the point of useful.
All in all I choose to buy the 200MHz model. The worse case samplerate is 1Gs/s which seemed pushing the limits too far at 300MHz (3.3 samples per period).
First impressionThe oscilloscope comes with four 300MHz probes, power cord, USB cable, a quick-start guide, MSO probe and a CD. The CD only contains the user manuals; no software. The oscilloscope does not come with a front cover which makes it less convenient to bring it to customers for measurements. I also would have preferred a real power switch. Even if it is at the back of the instrument. But then again high end Tektronix logic analysers don't have such a switch either. The probes are a bit flimsy even compared to the relatively cheap Testec probes I'm using. On the plus side they have a slim design like the Testec probes and they come with a complete set of accesoires.
All the options are enabled in trial mode. Instead of a time limit the options are available for a number of uses (30 times). So I don't have to hurry to try the AWG. Or just save it for when I just need an extra AWG channel.
DisplayWhat I'm missing is an option to inverse the video. I'm using a dark on white color scheme on all my equipment. It is much more pleasant to the eye (dark on white is standard in every PC application). The display on the SDS2000 also has a screensaver. Unfortunately that just hides the signals and shows the Siglent logo slowly bounching across the screen. What I would have liked is that it switches off the backlight. Even LED backlights have a finite lifetime.
MSO probeThe MSO probe comes with 10 EZ hook grabbers (made in USA) and leads. The probe set is an extension cord (the connectors are similar to those used for fast-SCSI) and a plastic box with a 2.54mm boxed header connector to connect the grabbers. The cable itself is a crappy 0.65 pitch ribbon cable which is easy to damage. Worst; most of these ribbon cables have a solid core so it is likely to have a very short life. I dug up a more rugged fast/ultra-SCSI extension cable from my cable box and that seems to work just as well. Would it be so difficult to include a cable like this?
http://www.ebay.com/itm/Adaptec-internal-wide-68-pin-SCSI-cable-1-meter-3ft-1496280-00-rev-a-/130466139871More complaining: all the grabbers and connecting cables are grey. It would have been nicer if 2 of them where black to indicate the ground connection. Because the MSO box doesn't have 'warranty void' stickers I opened it up and much to my surprise the analog front-end for the MSO part is in the plastic box! The specifications of the MSO bit are not stellar: 10pf input capacitance is rather high for a logic analyser especially with the input circuitry very close to the inputs. From the PCB layout it seems the digital signals are transported to the oscilloscope using differential (LVDS?) signals. If Siglent wants they could replace the analog front-end with something much better!
First measurementsAt first glance navigating through a signal seems to work OK. Zoom is a nice addition but if you are not capturing long traces adjusting the time/div and using the horizontal position knob works just fine. It is also nice that the units and probe attenuation factor can be freely adjusted. If you have a current clamp you can set the units to A with the proper multiplication factor. All in all the basic oscilloscope functionality seems to work as expected.
I tried decoding some serial data at 9600 baud. When the timebase is set slow it may be necessary to select a longer memory depth manually for decode to work properly. Much to my surprise the decode does not work for the digital channels! I bought this oscilloscope specifically for that feature!
I also did some tests with peak-detect mode. I used a signal generator to create pulses with a width of 16ns. The oscilloscope triggers fine but at settings of more than 200ms/div it doesn't display the pulses. The same goes for roll mode. The narrow pulses don't show. IMHO a fail because peak-detect is supposed to detect the narrowest pulses the front-end can handle. I guess peak-detect got implemented the wrong way; let the ADCs run at decreased sampling speed instead of downsampling while keeping min/max values. What this oscilloscope does is called 'envelope mode'. Actually my TDS744A can do both 'envelope' and peak-detect since these are two distinct different ways of acquiring a signal.
I'm also missing a 'menu off' button to hide a menu. The 'UP' button more or less works in a similar way of escape but it displays the message 'the page is top!' if you are already in the root menu.
Automated measurementsSo far I have only used the Vpp and frequency measurements. What I like about these is that the min, max, average and standard deviation are also shown. The values always tend to vary somewhat so having the extra information helps a lot to get a better feel for the signal you are looking at. To get stable readings on my TDS744A I have to switch the acquisition method to averaging with a lot of cycles. The downside is that the automated measurements are in the middle across the screen.
Bandwidth and aliasingBecause this is a realtime sampling oscilloscope with a bandwidth relatively close to the worse case nyquist frequency (500MHz) it is expected that the frequency response shows some peaking due to 'brick wall filtering'. I used an RF generator set to 0dBm (612mVpp on the oscilloscope) and set the input impedance to 50 Ohm. I forced the sampling frequency to 1Gs/s by enabling 2 channels. There is some peaking (maybe +/- 1dB) at some frequencies but nothing severe. On my 200MHz model the -3dB bandwidth is 345MHz. That is way more than I expected based on the specified bandwidth of 200MHz. When going beyond the nyquist frequency there is some residual signal due to aliasing. With the RF generator set to 1001MHz I see a 12mVpp sine wave with a frequency of 1MHz. With the 0dBM input signal the triggering is stable up to 450MHz. With the input sensitivity set to max (2mV/div) the oscilloscope still triggers on a 450MHz signal of -30dBm (less than 1mVpp) which is quite impressive.
The MSO partIt takes a bit of playing to get used to setting it up. The channels can be enabled individually and the order in which the channels are displayed can also be changed. Unfortunately things get weird when decoding is enabled. The digital channels get lost or work in the wrong way once the stop button is pressed or in single acquisition mode with decoding enabled. See picture below where the signal D0 (red) should display the same as channel1 (yellow). I think somehow the time cale for the digital channels doesn't follow the timescale for the analog channels. That is a major bug!
The MSO probe also has a clock input but I can't find a setting to use external clocking for the digital channels. IMHO the MSO part is still under development. A slight hint is that the 'Digital' button does not go off once the MSO part has been activated.
Dumping imagesI played a bit with dumping images. What I would like to have is a way to write the images with a white background. That looks much nicer in a report. I often make reports with screendumps from an oscilloscope. Having large black blobs in a document doesn't make it appealing. My TDS744A allows for writing images in reverse video (white background). Something else I'm missing is writing images in a different format. I would have expected to be able to choose between BMP, JPG and PNG but it seems only BMP is supported. Another option I'm missing is to dump the traces as CSV data. On my TDS744A I have used that feature to write a long trace to disk and process it further using Excel.
It would also be nice if the oscilloscope has it's own web server. That way a browser could be used to retrieve images and other data (sample values in CSV format). That would avoid needing to go back and forth with a USB stick all the time.
PC SoftwareI wanted to give the Easyscope3 software from Siglent a try as well but even after installing the NI-VISA software the software still says it can't initialise itself and terminates. I installed the software on a freshly installed Windows XP in a virtual machine. Not wanting to mess with finding compatible third party software versions endlessly I gave up on the software. I have the same problem with the software which came with my Siglent SDG1010. Siglent: please create software packages which 'work out of the box'! Having to install all kinds of third party software is way too cumbersome. Again: a webserver inside the oscilloscope would make it a lot easier than to having to mess around with software which needs to be installed first.
ConclusionAll in all there are several area's where bugs need to be fixed (also see the reviews of others). I was expecting that; I wanted to wait longer for the firmware to mature but an upcoming project forced me to either buy a CAN analyser or get the SDS2204 ahead of time. I also started to run into several limitations of my TDS744A. As it sits now I wouldn't recommend buying this oscilloscope if you can't work around the bugs that have been found so far.
Pros:
- low fan noise
- good triggering on low level signals
Cons:
- peak-detect is not doing peak-detect at all
- decoding doesn't work on digital channels
- flimsy MSO cable
At the moment I'm not quite sure whether I keep the oscilloscope or not. I'm not satisfied with the peak detect not working as it should and not happy with the decoding working on the analog channels only.
The same screendump showing the digital trace problem with decode enabled twice. Once normal (white on dark) and inverted (dark on white):