Photo of Siglent® SDS2202X.
I'll explain the picture in a moment.
Screen Size and Resolution.First, the screen is larger than I have ever seen on any bench scope, as opposed to rack mount units. The waveform display part of the screen measures 6 by 3.428 inches. The actual screen is larger than this because of menus on the right and bottom sides. The graticule is 14 by 8 divisions. Digital scopes have released themselves from the restriction of 10 by 6 imposed by a cathode ray tube. The resolution is 800 by 480 pixels.
Here is one of my little tricks.I'm sure most of you are constantly wondering how I am able to do electronics with the small amount of vision I have. I have only one eye that works at all. So it could be said that I am blind in one eye and can't see out of the other one. Well I can see just a little out of that second eye. I have a magnifying glass mounted in regular glasses frames so I can use the magnifier hands free. In fact I have three such glasses of different powers. I have to put my face very close to what I am looking at so pictures of me looking at a scope or analog meter aren't very flattering. (as if I worried about such things. I don't but my wife does.) Sometimes I have trouble reading the markings on controls because the designer used low contrast colors. This makes no difference to those with perfect vision but it makes a big difference to me. So when I get in a new piece of equipment the first thing I do is take a close up picture of the control panel. I print it out on 8-1/2 by 11 glossy photo paper and that becomes my way of reading captions that are unreadable on the actual instrument. The photo of the scope's control panel can be seen in the picture at the top of this page. When it comes to soft keys I have to rely on designers and manufactures to use large enough fonts, enough contrast, and brightness, to permit me to read them. So far, so good.
Testing the Limits.At 200 MHz the trace was as stable as it is at 1 kHz.
Screen Capture of 200 MHz Sine Wave.
The trace is not only steady but it is sharper than other DSOs I have tried. Also there are a number of things on the screen that may or may not need to be explained.
- In the lower left hand corner "CH1" indicates we are looking at channel 1. Duh.
- The legends across the bottom are this screen's labels for the soft keys.
- Input coupling is set to AC.
- Band width limit is off.
- The range switch is operating in the normal 1, 2, 5, sequence. As opposed to the fine setting which takes the place of the Vernier pot on analog scopes.
- A times one probe is being used. Simple BNC cables.
- The input resistance is set to one meg ohm. The alternate value as you probably guessed is 50 ohms.
- On the second page are the following.
- Units selection V or A (Volts or Amps)
- Something called Deskew which moves the actual trigger point off of the intersection point of the line drawn down from the position triangle at the top center of the screen, and the line drawn to the left from the trigger point at the right center of the screen.
- The third and last item on the second page is the invert mode, on or off.
- On the right hand side of the screen at the top the frequency is given with near frequency counter accuracy.
- Below the frequency readout the two lines in white seem to have something to do with sample rate and number of points. The sweep is on the highest range as indicated by the number to the right of the letter M next to the word Trigger (1.00 ns). The number indicated as Curr increases as the sweep is switched to slower speeds. The number indicated as Sa changes when the sweep time is set to very long values. As you can tell I don't understand the meaning of these numbers.
- The next box down tells the trigger source. It is in the same color as the trace that is the source of the triggering pulses. The number L is the amount by which the trigger level is off from zero.
- The next box gives the parameters of the channel that is turned on. If both channels are on there will be two of these boxes. In this screen shot the value of 200 mV/div is the setting of the volts per division control. The number below that is the amount by which the position control is offset from zero.
- The sweep setting is indicated by the number to the right of the letter M next to the word Trigger.
However, this is a review not an instruction manual. This is quite a lot of scope and it's going to take me time to learn all of its capabilities.
The fault is not in our scope but in ourselves.
Screen Capture of 200 MHz Sine Wave?
There is no problem with the scope, it is caused by a short between the ears. Note at the bottom of the screen the BW Limit is set to 20M (20 MHz). When you try to cram 200 MHz through a 20 MHz filter things are bound to overload and produce distortion. I did not intend to make this mistake but when I discovered it I realized it was a teachable moment. I am likely to make this mistake again because I live close to a tower holding two TV transmitters and a couple of FM stations to boot. I keep the filter on all the time and only turn it off when working above 20 MHz. That is, if I remember to.
DSO's Limitations on Viewing Two Signals with Widely Different Frequencies.Here is a scenario that engineers and technicians often set up.
Screen Capture of Amplitude Modulated carrier and modulating signal.
The carrier wave and audio signal have widely different frequencies. This is the third DSO I have set up with this signal input. This scope behaves much better than the other two I tried and one of them was a Tektronix. You might want to note a special setting that makes it work much better than I had anticipated.
I left the Acquire menu up for the screen shot. Note that the acquisition mode is set to "Eres". I don't even know how to pronounce that let alone know what it means.* In my defense I will say that the instruction manual has 200 pages and it's going to take me a long time to get through it with my CCTV reader. All I can say at present is "it works".
* See the section on the instruction manual.
X Y Mode.As you can see on the acquire menu this scope has an X Y mode. It behaves much better than on other DSOs I have used. When I set up two function generators with a frequency difference of 0.2 Hz and view one on each channel, the two sine waves drift smoothly across each other at a rate of one cycle every 5 seconds. When I invoke XY mode the familiar progression of positive sloping line - ellipse - circle - ellipse - negative sloping line goes in small jumps. However the pattern is very clean as you can see below. I don't know what they are doing but whatever it is, it works.
Screen Shot of Lissajous Figure as explained above.
Lissajous figures have fascinated me ever since I watched that science program that was introduced by a compound pendulum tracing a figure in sand on paper. I once used them to calibrate a homebrew audio oscillator. All I had were a very primitive army surplus scope, a tape recorder, the 60 cycle line, and the oscillator itself. The whole procedure is a subject for another page but I will give you a hint if you ever find yourself in a similar position.
As you probably know you determine the ratio of two frequencies by counting the number of tangents to a vertical and a horizontal line drawn along the edges of the figure. Here is an example.
Screen Shot of Complex Lissajous Figure.
I pressed the button at what you might suppose is the optimum time for tangency counting. If you have a keen eye you probably already have determined that this is an 8 to 9 ratio. Pretty, but hard to count the tangents. If you wait for a different time it becomes easier.
Screen Shot of Complex Lissajous Figure from above but taken at a different time.
If you wait until the lines fall on top of each other the figure is easier to read. Drawing the imaginary line across the top you see three loops and two lines. A loop is two tangencies while a line is one so across the top there are 8 tangencies. The bottom shows 4 loops which also adds up to 8 tangencies. Up and down the sides there are 4 loops and one line which adds up to 9 tangencies.
In that ancient time I was dealing with an analog tube oscillator in which the frequency control was a dual ganged pot. I could never make the pattern stand completely still. It was easier to catch this condition on the fly and count the tangents than to count the tangencies of the much busier figure.
Although I haven't tried finding the breakpoints of the frequency response of an actual audio amplifier I am fairly sure that it will be easier than with either an analog scope or one of the other DSOs I have used in the past.
Capturing the Image on the Screen.The first time you turn on the scope you will have to go into the "SAVE/RECALL" menu to set up the file format, the file naming convention and tell it to save to the USB drive. Once you have set that you won't have to bother with it again unless you want to change one of the parameters. After you set it up all you need to do is push the blue button.
Shooting the Screen.
The Lissajous figure stood still while a progress bar indicated that the screen was being read and transferred to the thumb drive. BTW, this group of Chinese engineers got the USB socket right side up.
A Nice Feature.You will note on several of the pictures that the probe is indicated as 1X. When one of the probes that is supplied with the scope is installed the mode changes to 10X. This is accomplished by a spring contact on the probe connector which closes a circuit informing the scope that a factory probe is installed. When the non probe (plain connector) is installed the user may set the probe value to anything from 0.1X to 1000X with 2 and 5 intermediate values for good measure. The value you set will be remembered but it will always revert to 10X when a supplied probe is connected. It will return to your set value when the probe is removed.
A Few Specifications.The vertical sensitivity (1X probe) goes from 1 mV/DIV to 10 V/DIV. This ratio is an order of magnitude more than the 1,000 to 1 found on older analog scopes.
The sweep rate just goes and goes and goes, from 50s/div to 1 ns/div. Let's see you do that with an analog scope. The screen is 14 divisions horizontally and 8 divisions vertically. That means a time of 700 seconds for one sweep on the slowest setting. That's 11 minutes 40.000 seconds. BTW, the divisions which were centimeters in the old Tektronix® days are approximately 7/16 inch on this scope. It is left as an exercise for the student to compute the size of the screen in (a) inches, and (b) Centimeters.
Cursors Improve the Measurement Accuracy.
It is much easier to set cursors and read the values than it is to count divisions, interpolate, and multiply by the range setting while remembering to take the X10 probe into account for voltage measurements. Some say that modern digital electronics has created a generation of lazy engineers and technicians. But I would never say a thing like that.
I had set the zero axis of the wave on the zero axis of the screen to set the X cursors. Then I raised it up so it wouldn't be behind the text box. The transparency of the box is adjustable but when it is set low the text changes from white on dark gray to black on white. I find the former easier to read and always select it when I have the option.
When you press the soft key under the rectangle with two vertical lines and two horizontal lines inside it, all four cursors appear but the most recently selected pair of cursors appears brighter than the other set. It is handy to have all four cursor lines on the screen at one time.
"Measure".This function is even easier than using cursors. Just select the measurement you want to make and it comes up on the screen. No more dividing by 2 times the square root of 2 to find the RMS value.
Cursors Improve the Measurement Accuracy.
As you can see the text for the measured value is tucked in between the menu and the bottom line of the graticule. There isn't really enough room here and it gives the appearance of having been an afterthought, even though it might not have been. I have to use my most powerful magnifier to read the values so I am not likely to use them very often.
"History".The history feature is rather like taking a motion picture of the screen. If you are just looking at a stationary wave it doesn't add any new information. But if you are looking at two waves with a slight frequency offset then it will show off its stuff. I'm not sure how I would use this in a serious measurement but I'll probably run into something when I least expect it. There is no screen shot because I can't use still pictures to show a movie.
Built in Function Generator.Since Siglent® makes some quite good stand alone function generators you might expect that the one built into an oscilloscope they make would be more than an afterthought. You would be right. The generator covers from 1 µHz to 25 MHz. That's right, one micro hertz. To save you the wear and tare on your calculator the period of 1 µHz is 11 days, 13 hours, 46 minutes, and 40.000 seconds. It will produce any wave you have heard of and a few you probably haven't. Custom waves may be loaded from a computer over the USB port. Available functions are,
- Square, (depends on Duty Cycle setting),
- Ramp (Triangular), Depends on Symmetry setting),
- DC, (set by offset value),
- Gaus Pulse, (Gaussian),
- Exp Rise, (Exponential),
- Exp Fall,
- And 4 slots for loading arbitrary functions.
The output impedance is 50 ohms all of the time. If you connect it to a high impedance load such as the input of an amplifier or one of the scope channels the maximum output will be 6 volts peak to peak. If you connect something that presents a 50 ohm load to the generator the maximum output will be 3 volts P-P. When you call up the generator menu by pressing the "WAVE GEN" button and press the "Settings" button you will see "Output Load" which can be set to "HiZ" or "50?". Changing this setting does not alter the output impedance, it merely changes the calibration of the output voltage.
The Manual.When all else fails…I'm sure you know that one. There is a lot to be learned from the manual especially for old analog hands such as myself. For example: did you know that the mode of the vertical attenuator can be toggled between coarse (normal) and fine by pressing in on the knob? I didn't think so.
Also the "Sa" and "Curr" values I mentioned earlier are sample rate in samples per second and memory depth in points respectively. I need a little more study to fully understand the meaning of memory depth but I'll figure it out.
Another personal note: The manual is provided on a CD ROM in the form of a PDF file. In the past this file format has presented problems for the blind and visually impaired. There have been improvements in recent months. Some files will be read by the screen reader quite smoothly. Unfortunately this one is not one of them. The reader reads the page that happens to be displayed at the time the file is opened and then stops. Nothing I can find will cause it to advance to the next page. My solution is to print the manual and use the OCR in my CCTV reader to read it. End of note.
The manual is nicely formatted and has only a few translation errors but there is one that can cause serious confusion. I came across an odd thing early in the manual. It refers to the roll button which allows low frequency waves to slowly scroll across the screen in the manner of a cardiac monitor. Next to a picture of the "Roll" button is this statement. "Quickly enter the roll mode. The timebase range is from 50 ms/div to 50s/div." My first impression was that the user was to press the button quickly. This seems unlikely and upon further consideration I think it means "Press this button to quickly enter Roll mode". I think it could be fixed by simply placing the word "To" before the word "quickly".
Under the heading "Universal Knob" on page 17, the photograph of the knob isn't the same as on the scope's panel. The description is clear however. Well, I'm not going to go through the entire manual to find every error on every page. I imagine the folks at Siglent would rather like that. I liked it when someone did that for my website. (New pages have been added since he did that so I have no doubt that more errors have crept in.)
In this scope the old "delayed sweep" function that we once used to look at a single line in an SCNT video frame is called "zoom". Now that you know what it is called you can read all about it.
I have found another error which although small on its face could cause someone not already familiar with the Nyquist criterion to fail to understand it. It is under the discussion of sampling theory on page 36. The equation is given as
fMAX = fs/2 WRONG!
fMAX = fs/2 correct.
This is the kind of mistake that would not be caught by an English major.
I found out what "Eres" stands for and what it is doing. It is an abbreviation for "Enhanced Resolution". It is a digital filter for reducing noise. I don't completely understand why it provides so much improvement for an amplitude modulation envelope but I'll take it and run with it.
Conclusion.This is truly a quality oscilloscope. It meets all specifications and everything works the way it is supposed to. The screen is large and easy to read, with one exception, and the controls are intuitive for an experienced DSO user. I recommend to anyone who wants a quality scope to save up your pennies and buy this one.
Dimensions: 14 x 9 x 5-1/2 inches including knobs.
Price (MSRP): $1595.00. At this writing the scope is advertised with a sale price of $1116.00 but the fine print states that the sale expired June 1, 2017. Yet it is still listed for the sale price. I suggest that a phone call to their 800 number would be in order.
Find it at this location.