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1

Test Equipment / Re: Siglent SDS800X HD Review & Demonstration Thread

« Last post by Performa01 on Today at 07:31:43 am »

I was playing with SDS814X FFT math (Hanning window) comparing results with my SSA3021X (Gaussian filter), in attachment some screens of 50MHz 0dBm CW sine wave (from SDG2042X) with different SPAN / RBW.

I would lik to know your opinion about SDS814x spectrum images @ 100Hz RBW, there is something wrong.

Am I doing something wrong or am I pushing the measure system over some limit ?

The first thing I noted was the seemingly random usage of window functions. Hanning and Gaussian are not comparable and for a meaningful test we should stick with the Flattop window on both instruments.

Then I wonder how the signal can actually be 50 MHz / 0 dBm. If so, then the SSA shows a level error of -0.91 dB, which might be attributed to the Gaussian window. But even the rather unsuitable (for spectrum analysis) Hanning window cannot explain a +0.97 dB amplitude error on the SDS800X HD.

Let’s compare the first test with 30 kHz RBW now:

 
SDS824X HD_FFT_50MHz_0dBm_RBW28kHz

Now compare this with the SSA screenshot. The SDS level measurement isn’t too far off at -0.288 dBm, the filter shape factor is as expected for a spectrum analysis and the noise floor is <-90 dBm. At 51 MHz that is some 20 dB better than the SSA – and the difference would be even greater if we measure closer to the carrier.

Next is 1 kHz RBW:

 
SDS824X HD_FFT_50MHz_0dBm_RBW900Hz

Yes, we see some modulation sidebands below -72 dBm now, and again we cannot decide if they would be visible on the SSA as well, as the noise floor there completely masks everything that low. By contrast, the SDS800X HD shows a noise floor of -100 dBm.

But we can try the same scenario with a higher class DSO, like the SDS2000X HD:

 
SDS2504X HD_FFT_50MHz_0dBm_RBW700Hz

This proves that the signal source is clean and the spurious modulation happens within the SDS800X HD somehow.

Finally 100 Hz RBW. This just isn’t possible at 50 MHz – the SDS800X HD is a DSO, hence a baseband instrument and not a spectrum analyzer. The FFT would need to compute at least 4 Mpts to handle this.

Yet we can try to come as close as possible: using the full 2 Mpts at 250 MSa/s we can get about 440 Hz RBW with the Flattop window. In a pinch we could use the Blackman window, which has still acceptable amplitude accuracy and a great side-lobe suppression. This way we can get ~200 Hz RBW:

 
SDS824X HD_FFT_50MHz_0dBm_RBW200Hz

Yes, there are those spurious modulation sideband signals again, and these are not visible on an e.g. SDS2504X HD:

 
SDS2504X HD_FFT_50MHz_0dBm_RBW165Hz

So yes, the SDS800X HD has a problem there. Since the FFT should be the same across the platform, this is more likely to be a hardware issue.

In attachment 2 additional spectrums of 50MHz carrier AM modulated with 1KHz sine wave, 100%.

Once again, 1 kHz is a tough request. It is just about manageable:

 
SDS824X HD_FFT_50MHz_0dBm_RBW200Hz_Mod1kHz

Yet a closer look reveals a 10 kHz modulation frequency for the provided examples anyway, so here we go:

 
SDS824X HD_FFT_50MHz_0dBm_RBW200Hz_Mod10kHz

Yes, there are various spurious signals again. On the SDS200X HD we get the third order intermodulation products only:

 
SDS2504X HD_FFT_50MHz_0dBm_RBW165Hz_Mod10kHz

These are not unexpected though. A wideband amplifier can only have so much linearity, and I’ve covered this topic in more detail here in this thread (reply #6, section “Distortion Measurements”):

https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5293759/#msg5293759

The main source of distortion in a modern DSO frontend would be the PGA, where third order intermodulation distortion is specified as -65 dBc (typically) at 250 MHz. Harmonic distortion is even worse at -50 dBc (typical) at 100 MHz. Both SDS meet the expectations at ~-67 dBc.

https://www.ti.com/product/LMH6518

BTW, in the SDS800X HD datasheet, the spurious-free dynamic range SFDR is specified as only ≥35 dBc.

Same topic, comparison with DHO1000 that does not show unwanted spuries :

Yes, that’s quite amazing. As stated above, such distortion figures cannot be expected with industry standard parts like the LMH6518.

2

Test Equipment / Re: FNIRSI-1013D "100MHz" tablet oscilloscope

« Last post by Atlan on Today at 07:26:57 am »

If you measure a DC voltage of 7.5V, a DC shift is created. Is the signal located in the center of the screen? Is it the same on both channels or are there differences?

3

Beginners / Re: Extracting the mains frequency clock without adding a phase shift artifact?

« Last post by Xena E on Today at 07:18:19 am »

In a situation as I understand your requirement, my approach would be generate a zero crossing pulse to lead the actual point of of ZC and then introduce an accurate variable delay.

In a recent project, a pulse was created that detected the point where the line voltage had fallen below a convenient  and accurately defined level, with as small a leading phase angle as practically possible to preseve the system accuracy. The leading edge was used to define the following synchronisation, which was done in code.

(The peak level of the incoming supply was also monitored to prevent that translating into phase errors.)

Regards,
Xena.

4

Test Equipment / Re: New handheld touch DSO, Fnirsi 2C53P, claimed 50MHz/250MSps (April 2024)

« Last post by csuhi17 on Today at 07:14:16 am »

I found a test on the Internet, only a few pictures and text.
I managed to interpret it in such a way that the first series may have some physical problem, and whoever bought it just now will most likely have to return it. 

https://www.mydigit.cn/forum.php?mod=viewthread&tid=451205

5

Repair / Re: Power Fuse

« Last post by Farah on Today at 07:10:42 am »

Thanks for your Reply.
The output of this PSU is only used to turn on a 100 watt/110VAC UV lamp (Mercury). The power supply of the lamp fan is from another board. There is no information on the body of the device, board, etc.

6

Projects, Designs, and Technical Stuff / Re: what certification is required to sell electronic products?

« Last post by strawberry on Today at 07:03:14 am »

same when handling returns. incident happened when someone bought kids toy with removable battery and same service rejected sending it back because it is lithium
I suspect they earn cents from UPS etc and dont want to dig into legal stuff.
I think, they know how to design products so that they get less returns

7

Test Equipment / Re: Keysight 34450A Help

« Last post by Simon on Today at 07:01:32 am »

DO NOT DOUBLE, TRIPLE....... POST. EVERYONE WILL HATE YOU.

8

General Technical Chat / Re: H5N1 bird flu and how we're risking another global pandemic

« Last post by Simon on Today at 06:59:52 am »

Then there's all the other misinformation exaggerating the efficacy of masks, keeping 2m apart etc. which lacked rigorous evidence to support and the authoritarian policies copied from Communist China. It appears as though the public health authorities did their level best to destroy their reputation.

And what proof is there that distancing does not work?

It isn't. I didn't say that it's proof that masks and keeping 2m apart don't work, just that there's no strong evidence they do. The Cochrane review into masking found it to be inconclusive and as far as I'm aware no studies have been conducted into whether keeping 2m apart does anything to reduce the spread or not. And why 2m? Perhaps 1m would have done? Or maybe we needed to keep 3m or 5m apart? Where's the evidence?

It would be different if we were just advised to wear masks and keep 2m apart. That wouldn't have been ideal, given the lack of evidence, but the fact we were forced to, under pain of a fine, is disgusting. If the authorities are going to punish people for breaking rules, then there needs to be extremely strong evidence to support them in the first place.

Both distancing and masks rely on basic physics! You want a study? go an throw some tennis balls and notice that the further they go the closer to the ground they get. And that if you through them as several layers of nets they will no go nearly as far. What you are asking for in the equivalent to arguing about the distance to the moon because a tape measure was not used.

9

Test Equipment / Re: Enabling options on Agilent ESA series E4402B E4404B E4405B E4407B

« Last post by BG8IP on Today at 06:41:20 am »

HELL PAOPBZ SEEING CABLE FAULT LOCATION FUNCTION  IS A PRACTICAL FEATURE FOR HAM     
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      J36                                                                                                           
                                                                               THANK YOU

10

Projects, Designs, and Technical Stuff / Re: Soldering in a life circuit

« Last post by coppercone2 on Today at 06:36:03 am »

the AA battery ones are OK just don't expect it to work a long time.

Butane is IDK, if you have a soldering iron calibrator to set it properly OK, otherwise the battery one is better.

Now the USB c ones are probobly pretty good and run on powerbank etc, but if its just like for the rarest of rare uses, the AA one is a better value IMO, because its cheap Built in lithium battery one sare better, so long it has replaceable battery, because u know you will use that once every 5 years