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Siglent SDS1104X-E In-Depth Review

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nctnico:

--- Quote from: Performa01 on February 23, 2018, 11:34:14 pm ---Just to make sure no one gets alienated or confused by a couple misleading statements I’d like to assure you that probe manufacturers are no cheats. They don’t sell passive high-Z probes rated up to 500MHz just for fun.

--- End quote ---
IMHO they do. Just do the math when taking the probe capacitance at the tip into account. Usually that capacitance is in the 10pf ball park. At 500MHz the circuit is loaded with a 31 Ohm impedance. With an active FET probe or low-Z probe you'll get a way more true representation of the signals you are measuring. One thing people shouldn't forget is that 'to measure is to interfere'. Less interference means you get more accurate results.

Performa01:

--- Quote from: nctnico on February 23, 2018, 11:41:37 pm ---
--- Quote from: Performa01 on February 23, 2018, 11:34:14 pm ---Just to make sure no one gets alienated or confused by a couple misleading statements I’d like to assure you that probe manufacturers are no cheats. They don’t sell passive high-Z probes rated up to 500MHz just for fun.

--- End quote ---
IMHO they do. Just do the math when taking the probe capacitance at the tip into account. Usually that capacitance is in the 10pf ball park. At 500MHz the circuit is loaded with a 31 Ohm impedance. With an active FET probe or low-Z probe you'll get a way more true representation of the signals you are measuring. One thing people shouldn't forget is that 'to measure is to interfere'. Less interference means you get more accurate results.

--- End quote ---

Of course you are right – it is not at all straightforward to probe high frequencies and people should always keep that in mind. And yes, I agree that 500MHz takes it to the extreme and the number of possible applications is reciprocally proportional to the frequency.

But confirming probe performance up to 300MHz is perfectly possible with 25 ohms source impedance, even though it might appear pointless, given the (low) number of practical uses.

The initial question was about rise time and I always like to check the frequency response too, as it provides additional information helpful for understanding the odd behavior we might see in the time domain.

Performa01:
Some of you (any tube aficionados around?) might be interested in the performance of a HV (high voltage) probe, so I wanted to add the TesTec TT-HV250 (x100) to the comparison. This turned out to be much more difficult than expected and inspired me on touching another topic as well: probe performance with the supplied ground leads.

The TesTec TT-HV250 is a 300MHz rated 2.5kV x100 probe which means that even with a HF signal source capable of delivering rather high levels like 1.5Vrms into 50 ohms, the scope will still only see 15mVrms. In all my previous tests I had used 400mVrms with x10 probes, hence 40mVrms at the scope input. I would have liked to keep all test conditions equal, but that was just not possible for a x100 probe.

This was still the easy part. This probe does not have a metal shell around its neck, hence the BNC adaptor supplied with that probe cannot make ground contact. Do they even think at TesTec?
Even worse, there is absolutely no means for a ground connection at all, other than the slot where the ground lead is to be clipped in. So I had to use that – for a 300MHz rated probe, take notice please!

The results were as expected – or maybe even not quite as bad as that. Of course you get no chance to ever probe a 300MHz signal with a probe that forces the use of the ground lead – and it shows. But then I though it might be beneficial to demonstrate the performance (or lack of) for an ordinary PP215 with ground lead as well, because this is what many of us will be using most of the time.

First comes the frequency response graph. Dark blue for the TesTec TT-HV250 and orange for the Siglent PP215. As a reference I have included the results for Siglent PP510 (green), which performs very similar to the PP215, as well as Pico Tech TA131 from the last test (with BNC adaptor).


SDS1202X-E_Probe_Comparison GL

We can see that the TesTec TT-HV250 performs quite normal up to 70MHz and still reasonable to about 100MHz, but goes increasingly haywire beyond that. It is quite surprising that it still remains within +/-3dB up to 180MHz – I wouldn’t have expected that. Above that frequency, it really gets dramatic and the 300MHz rating for this “groundless” probe can only be a bad joke.

The Siglent PP215 responds even more allergic to the ground lead and can only be used up to 30MHz without major issues. Hopefully this demonstration helps make users aware of the frequency limit for safe use of the ground lead – “safe” in the sense of still getting reasonable measurement results.

Of course my findings can only be some guide to give you an idea what to expect. Shape and area of the loop antenna formed by the ground lead affect the performance and maybe it would have been possible to tweak it for slightly higher frequencies, But then again, we usually move the probe hence also the ground lead while probing, thus any tweaking would be irrelevant for practical work.

Finally let’s have a look at the pulse responses:


SDS1202X-E_Probe TesTec TT-HV250 GL


SDS1202X-E_Probe  Siglent PP215 GL

The screenshots confirm what we could have predicted from the frequency response graph: the PP215 is much more violent when using the ground lead. The rise times are notably worse than with proper ground connection as well. By comparison, the TesTec TT-HV250 pulse response looks surprisingly benign.

rf-loop:
I have been wondering one thing.

In SDS1000X-E Bandwidth.pdf  there is example this image:

Square_50MHz_BW111MHz_500MSa_Dots

(also some other using dot mode)

I have some intuitio that perhaps there need be some re-thinking what it is or what combination about things leads this shape. This same kind of behavior exist also in SDS2000 series. Is it "aliasing" as we normally think what is aliasing. My hypothese is that not, or least some part is not aliasing.

I do not know how this trigger - fine interpolation - fine positioning system works and what kind of interpolation it do between real sample points for fine adjust this interpolated "imagined" point in signal to trigger time position.
Some very sophisticated scopes may do also there Sinc interpolation but with fast look it somehow looks like that there Siglent do linear interpolation (I do not mean this Sinc what we look in display what interpolate through displayed true samples. I think here fine interpolation between true sample points for fast fine adjust every single acquisition signal on display for minimalize time error in positioning. )
Perhaps this thinking is  meaningless but I'm somehow interested still how it produce these "fun" shapes in dots mode when we go to fast changes in signal related to sample rate. 
I have done some tests with SDS1104X-E and SDS1202X-E (Serial "BB" hardware) but they are not exactly comparable due to different input reactances (example 4 channel nominal input is 15pF and 2 channel model nominal is 18pF what leaads to different mismatch using feed thru termination - with fast risetimes this matters) so it need also bit thinking about what is what when look result images but this is now here quite meaningless.


ETA1:I will later, after test data gathering and organizing, add some images to "Siglent SDS1104X-E and SDS1204X-E Mixed Signal Oscilloscopes" for avoid extra hassle or possible highway to huge O.T. debate in this extremely good deep review thread.
They show well how 100MHz model is bit more protected from some aliasing due to different front end bandwidth before ADC.
ETA2: It takes more time. Problem is some tests made using SDS1104X-E FW .20 where is really some things out of order.  (there is perhaps much more wrong than just trace display disappear in some cases).

Performa01:
The first implementation of the MSO option has become available with firmware 7.6.1.20 and I’ve received the SLA1016 digital probe about a week ago. Unfortunately the Sbus cable was missing and even though the connectors are identical, an HDMI cable cannot replace it. So I have to wait until I get the original one.

Until then, I’ll show some details of the hardware. First the contents of the box (minus the Sbus cable):


SLA1016_Set 01

Top left is the interface box SLA1016 that connects to the SDS1004X-E through the Sbus cable at one end. The other end has a 2x34 connector for the ~80cm long high density flat ribbon cable, which in turn connects to the SPL1016 probe head. It is connected in the picture above, but can easily be detached.
The opposite side of the probe head has two standard 1/10” 2x8 pin male connectors where the supplied probe leads can be connected as well as user specific probes, e.g. with a 16 wire flat ribbon cable on a standard 1/10” 2x8 female header.

The two supplied probe leads consist of a 1/10” 2x8 female header with eight 140mm long digital input leads and two 100mm long ground wires. At the end of each wire there is a metal sleeve that connects to 0.64mm pins on hooks or any other test points/connectors.

Finally there is a bag with 20 cheap hooks.


The picture below shows the SPL1016 probe head. It has the relevant specifications printed on it as well as the connector layout and the color scheme for the supplied probe leads.


SPL1016_Head 01


The next image shows the probe connector side of the SPL1016 head together with one probe lead assembly and a hook.


SPL1016_Head 02


The tip of one of the hooks supplied with the SPL1016 is shown below. The diameter of the plastic sleeve is 1/10”.


SLA1016_Hook


Compare this with the E-Z hook (made in USA) supplied with the SPL2016 digital probe head that is an option for the SDS2000(X) oscilloscopes. The quality is appreciably better and the plastic sleeve has only 1/20” diameter at the tip.


SPL2016_E-Z-Hook


As a consequence the noname hooks supplied with the SPL1016 can only connect every other pin on a SOIC with 1/20” pin spacing, whereas the SPL2016 hooks can connect eight adjacent SOIC pins in a row if required.


Digital_Hooks_Spacing


Thankfully this is not an ultimate limitation for the SPL1016, because the E-Z Hooks (and probably most others) can be used together with the SPL1016 without any problems as shown below.


Digital_Hooks 01

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