Another radio amateur about to buy a DSO ...

[Mike99]

After reading many threads on the subject here and suffering from the resulting analysis paralysis I have almost decided to go for a Siglent SDS1202X-E.

One very helpful post from a couple of years ago showed that it has a 3dB bandwidth of around 300MHz which is fine for me as I work mostly below 50MHz.

I also read about input noise, and how some scopes use relays to switch attenuators while others use tapped resistors. Does anyone know which way Siglent goes?

Mike

[Performa01]

After reading many threads on the subject here and suffering from the resulting analysis paralysis I have almost decided to go for a Siglent SDS1202X-E.

One very helpful post from a couple of years ago showed that it has a 3dB bandwidth of around 300MHz which is fine for me as I work mostly below 50MHz.

I don't know which post you're referring to, but actual measured -3 dB bandwidth of an SDS1202X-E is about 240 MHz. I have no reason to believe that the SDS1204X-E would be any different. Much more important, the amplitude drop for most Siglent DSOs usually won't eceed -1 dB at the rated bandwidth.

Reliable (but partially a little outdated) information on all the properties of the SDS1000X-E series can be found in this thread:

https://www.eevblog.com/forum/testgear/siglent-sds1104x-e-in-depth-review/msg1371771/#msg1371771

I also read about input noise, and how some scopes use relays to switch attenuators while others use tapped resistors. Does anyone know which way Siglent goes?

I'v never heard of "tapped resistors" in a DSO. All DSOs I'm aware of are using proper attenuators, yet there is a difference in implementation: many cheap instruments make do with just one attenuator for the entire vertical sensitivity range, whereas the SDS1000X-E has two of them (like the big boys), which enables a more optimal amplitude scheme and lower noise indeed in certain situations. On top of that, the SDS1000X-E  is one of the very few DSOs with a true (full resolution) 500 µV/div setting. Others appear to have high sensitivities too, but these are mostly just softare magnifications which costs resolution and doesn't help to increase the SNR.

[RoGeorge]

You'll have to set a max budget before talking what to buy.

I would look for something with (in this order):  4 channels, 12bits ADC, 50 ohms input option, an internal generator channel (AWG) would be nice for bode plots.  Siglent and Rigol are trustworthy brands while still affordable. 

In terms of bandwidth, in practice it's not much of a difference between 100 or 200 MHz.  The logic analyzer option doesn't matter either, for the price difference usually there are better standalone USB LA.

Both Rigol and Siglent can be unlocked, so for hobby use might worth buying the smallest model for a given series, then unlock it (for free) to its max performance and max software options.  The hardware is the same for each given products line.  This may add a lot of value for Rigol and Siglent, when compared with other not so hacking-friendly brands.

[tggzzz]

Points to watch out for, which might indicate a scope isn't the best tool for your requirements...

Ignore headline figures, and understand how the "ENOB" affects distortion (time domain) and harmonics (frequency domain) analysis.

Verify whether post-processing (e.g. FFT, protocols) operates on the entire captured buffer or just that portion which is visible on the screen. Understand the consequences of the buffer size w.r.t. frequency domain analysis.

IMHO if you are interested in harmonics then consider a spectrum analyser for RF work, or a sound card for audio work. If you are interested in "higher level" radio signal analysis, consider an SDR.

[Fungus]

After reading many threads on the subject here and suffering from the resulting analysis paralysis I have almost decided to go for a Siglent SDS1202X-E.

The choice would be between that and the new kid on the block, the Rigol DHO802.

Prices are similar, overall capabilities are similar, but the Rigol is more modern (eg. touch screen and windowing) and has 12-bits. Also HDMI out, VESA mount...

For both of these you'd buy the base model and hack them to full bandwidth. Measured bandwidth would be about 200Mhz on the Rigol.

Dave compares the FFT abilities here:

[Fungus]

Verify whether post-processing (e.g. FFT, protocols) operates on the entire captured buffer

I don't think any low end model DSO does that. Rigol and Siglent are both limited to 1Mpts.

[tggzzz]

Verify whether post-processing (e.g. FFT, protocols) operates on the entire captured buffer

I don't think any low end model DSO does that. Rigol and Siglent are both limited to 1Mpts.

I strongly suspect that is the case.

I haven't investigated what high-end expensive scopes achieve.

[G0HZU]

I'v never heard of "tapped resistors" in a DSO. All DSOs I'm aware of are using proper attenuators, yet there is a difference in implementation: many cheap instruments make do with just one attenuator for the entire vertical sensitivity range, whereas the SDS1000X-E has two of them (like the big boys), which enables a more optimal amplitude scheme and lower noise indeed in certain situations. On top of that, the SDS1000X-E  is one of the very few DSOs with a true (full resolution) 500 µV/div setting. Others appear to have high sensitivities too, but these are mostly just softare magnifications which costs resolution and doesn't help to increase the SNR.

Take a look inside a Rigol 5000 series scope. There's a front end relay to select to the 50R path (and the 50R path looks to have a relay controlled attenuator) but the main 1Meg path is all done using a series of tapped resistors that feed to the first input IC via the various taps. There are no relay controlled attenuators on the 1Meg path. If you look at the resistor arrangement, you will be able to work out how it maintains a 1Meg input (for all the taps) but it inevitably does this in a lossy way. There's always a big fixed resistive divider at the input on every range. This fixed divider spoils the signal to noise ratio.

Other scopes can deselect the attenuators using relays allowing much better noise performance on the sensitive ranges.

So I'd expect the Rigol 5000 series scopes to have very high noise levels on the sensitive ranges on the 1Meg input. I've never used one but plenty of people complain that they are noisy.

[G0HZU]

You can also look inside some of the budget Tek scopes to see a similar arrangement using fixed and tapped potential dividers. There are no relays involved in the selection of the attenuation ahead of the front end IC. These scopes will also be noisy on the sensitive ranges because of the fact that there is always some fixed attenuation involved even on the most sensitive range. Hence the signal to noise ratio is degraded.

It's very similar to how you can observe how any scope gets noisy with a x10 scope probe fitted. The resistive divider in the probe degrades the signal to noise ratio seen on the display once the scope is set to x10 probe mode. The cheapo scopes that use the tapped dividers will suffer the same degradation in signal to noise ratio because there is always a fixed divider at the front end. You can easily spot it because it will be a large SMD resistor rated for high voltage and it will be somewhere in the region of 750k ohm. It will have some compensation capacitance in parallel with it. This can't be deselected so these scopes are designed to (inevitably) have a degraded signal to noise ratio on the most sensitive ranges.

[Mike99]

Thanks everyone. I think you're telling me that the Siglent uses relays to switch the attenuators.

I already have a quality SDR with spectrum analyser software so I'm only looking for oscilloscope functions. My current scope is a Tek 2430A - big, noisy, heavy.

As for budget, ideally no more than £500 so I could afford the Rigol DHO812 (I don't need 4 channels for what I do) but it's only 100MHz bw and I don't like the front panel layout. At a push I could go for the Siglent SDS2202X-E.

A 50 ohm input would be useful but I was planning to use a feedthrough terminator.

Mike

[RoGeorge]

Rigol DHO812 (I don't need 4 channels for what I do) but it's only 100MHz

DHO900 goes up to 250MHz, but I don't have it so no idea how it is.
https://www.rigolna.com/products/rigol-digital-oscilloscopes/dho900/

[Mike99]

Rigol DHO812 (I don't need 4 channels for what I do) but it's only 100MHz

DHO900 goes up to 250MHz, but I don't have it so no idea how it is.
https://www.rigolna.com/products/rigol-digital-oscilloscopes/dho900/

It's too expensive for me (£740).

Mike

[Fungus]

As for budget, ideally no more than £500 so I could afford the Rigol DHO812 (I don't need 4 channels for what I do) but it's only 100MHz bw and I don't like the front panel layout. At a push I could go for the Siglent SDS2202X-E.

That's what it says on the front but real-life measurements show it's much higher.

A lot of people here have bought the 70MHz model and unlocked it to 100Mhz with a license key generator. Measured bandwidth on the unlocked 'scopes is 200MHz (I've measured mine, several other people have measured theirs and got this result).

eg. Here's Martin72 measuring (via rise time) 125Mhz bandwidth on a "70Mhz" model and 200MHz bandwidth on a "100MHz" model.
https://www.eevblog.com/forum/testgear/split-from-rigols-new-dho800-oscilloscope-unbox-amp-teardown/msg5156580/#msg5156580


Why is Rigol underselling the DHO800? We don't know. We only know it's a marketing decision.

[Mike99]

Yes I know these can be hacked but I would be reluctant to try until it's out of warranty.

Mike

[ebastler]

Take a look inside a Rigol 5000 series scope. There's a front end relay to select to the 50R path (and the 50R path looks to have a relay controlled attenuator) but the main 1Meg path is all done using a series of tapped resistors

I don't think the MSO5000 has an internal 50 Ohm input path at all. Are we thinking of the same scope here?

[tautech]

At a push I could go for the Siglent SDS2202X-E.

A 50 ohm input would be useful but I was planning to use a feedthrough terminator.

You do get more features with 2kX-E models.
1M/50 Ohm input path.
Webserver
Bode plot
WiFi

And it's a 350 MHz design......

[RoGeorge]

I would be reluctant to try until it's out of warranty.

The unlock is a number.  Can be manually introduced, or removed at any time.  Won't void the warranty.

[Mike99]

At a push I could go for the Siglent SDS2202X-E.

A 50 ohm input would be useful but I was planning to use a feedthrough terminator.

You do get more features with 2kX-E models.
1M/50 Ohm input path.
Webserver
Bode plot
WiFi

And it's a 350 MHz design......

Now that's interesting. If I bought the SDS2202X-E (200MHz) could I open it out to 350MHz?

Mike

[G0HZU]

Take a look inside a Rigol 5000 series scope. There's a front end relay to select to the 50R path (and the 50R path looks to have a relay controlled attenuator) but the main 1Meg path is all done using a series of tapped resistors

I don't think the MSO5000 has an internal 50 Ohm input path at all. Are we thinking of the same scope here?

Whoops, sorry for any confusion caused. It turns out that I was describing the Rigol 7000 scope. I was watching Dave's Rigol 5000 teardown and he had overlaid a screenshot of the 7000 front end. I got the two mixed up and it's only the 7000 that appears to have the 50 ohm path.

Both of them appear to have the tapped resistive network on the 1Meg path though. They look very similar in this respect so I'd expect both of them to be quite noisy because of this.

[2N3055]

Take a look inside a Rigol 5000 series scope. There's a front end relay to select to the 50R path (and the 50R path looks to have a relay controlled attenuator) but the main 1Meg path is all done using a series of tapped resistors

I don't think the MSO5000 has an internal 50 Ohm input path at all. Are we thinking of the same scope here?

It does not. You need to step up to DS/MSO7000 for 50 Ω Path. Also only DHO4000 has it..

[2N3055]

Take a look inside a Rigol 5000 series scope. There's a front end relay to select to the 50R path (and the 50R path looks to have a relay controlled attenuator) but the main 1Meg path is all done using a series of tapped resistors

I don't think the MSO5000 has an internal 50 Ohm input path at all. Are we thinking of the same scope here?

Whoops, sorry for any confusion caused. It turns out that I was describing the Rigol 7000 scope. I was watching Dave's Rigol 5000 teardown and he had overlaid a screenshot of the 7000 front end. I got the two mixed up and it's only the 7000 that appears to have the 50 ohm path.

Both of them appear to have the tapped resistive network on the 1Meg path though. They look very similar in this respect so I'd expect both of them to be quite noisy because of this.

You are correct. They are noisy..

[tautech]

At a push I could go for the Siglent SDS2202X-E.

A 50 ohm input would be useful but I was planning to use a feedthrough terminator.

You do get more features with 2kX-E models.
1M/50 Ohm input path.
Webserver
Bode plot
WiFi

And it's a 350 MHz design......

Now that's interesting. If I bought the SDS2202X-E (200MHz) could I open it out to 350MHz?

Yup. Not difficult at all.

IIRC -3dB BW =~400 MHz

Member xrunner posts about his here:
https://www.eevblog.com/forum/testgear/oldish-vs-newish-test-equipment/msg4685039/#msg4685039

[tggzzz]

At a push I could go for the Siglent SDS2202X-E.

A 50 ohm input would be useful but I was planning to use a feedthrough terminator.

You do get more features with 2kX-E models.
1M/50 Ohm input path.

Are they 50ohm inputs or 1Mohm//50ohm//15pF inputs?

What's the VSWR, which is relevant at RF frequencies?

[tautech]

At a push I could go for the Siglent SDS2202X-E.

A 50 ohm input would be useful but I was planning to use a feedthrough terminator.

You do get more features with 2kX-E models.
1M/50 Ohm input path.

Are they 50ohm inputs or 1Mohm//50ohm//15pF inputs?

What's the VSWR, which is relevant at RF frequencies?

https://int.siglent.com/u_file/document/SDS2000X-E_DataSheet_DS0102E-E02A.pdf

[tggzzz]

At a push I could go for the Siglent SDS2202X-E.

A 50 ohm input would be useful but I was planning to use a feedthrough terminator.

You do get more features with 2kX-E models.
1M/50 Ohm input path.

Are they 50ohm inputs or 1Mohm//50ohm//15pF inputs?

What's the VSWR, which is relevant at RF frequencies?

https://int.siglent.com/u_file/document/SDS2000X-E_DataSheet_DS0102E-E02A.pdf

VSWR isn't specified, which often happens where the manufacturer just puts a 50ohm resistor in parallel with the 15pF 18pF.

Any chance you could put a VNA on one of yours, in order to settle the issue?