Author Topic: Help with Rigol DS4014E on 10MHz external ref  (Read 1941 times)

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Offline picitup

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Help with Rigol DS4014E on 10MHz external ref
« on: February 04, 2018, 12:32:42 am »
Hi All

I'm trying to drive the timebase of my DS4014E from my BG7TBL gpsdo and am unable to convince myself it's working.

The documentation for this feature is very poor and after a number of emails to Rigol I managed to extract from them that the external clock is 10MHz, 1-4vpp square or sine wave and is a high impedance input.

However, after connecting the gpsdo to the external clock BNC at the back, I chose the Utility menu, RefClock and ClockInput but I can't see any indication it's working.  There doesn't seem to be any display annunciator to show it's external and the 10MHz hardware counter shows 10.0000 MHz both on Internal and external clock.

Also if I choose the Horizontal menu on the left and add a Frequency label, the readings dance around between 9.96 and 10.04 MHz.

Has anyone successfully proved the 10MHz external input works?

I'm letting it cool down now and will try again later with the internal clock and the GPSDO and maybe the frequency will be off a bit when it's cool and internally clocked and perfect if it's switched to external.

I must admit that with the poor documentation, difficulty extracting the specs from Rigol and unable to see any changes it makes me wonder if it works at all.

Cheers

Steve
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Offline picitup

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Re: Help with Rigol DS4014E on 10MHz external ref
« Reply #1 on: February 04, 2018, 02:37:54 am »
Well I think I've just realised my fears.  I don't think the 10MHz input works.  When I select the external clock, I can hear the reassuring clunk of a relay, but that's not helping much.

I just connected my SDG1025 sig gen to the external input and a 10MHz gpsdo signal to CH1 and turned on the hardware counter. 

The sig gen was set to 10MHz sine wave @3.3v pp and the scope displayed the sine wave from the gpsdo and the scope freq. counter displayed 10.0000 MHz.

I then adjusted the frequency of the sig gen slowly down to 9.5MHz.  I expected the sine wave and frequency counter to change with the incorrect external reference frequency but no change.  I tried adjusting the sig gen output to 3.9v, tried a square wave and tried adjusting the frequency down to 1MHz and up to 15MHz but no change.

So I think it's buggered.  >:( As a point of interest, if you set the clock to external on the sig gen and unplug the connection, it provides no output which makes sense, I think.  On the scope if you set it to external and unplug the cable, it all works fine and there's no visible change.

Has anyone actually got this working?  Am I missing something?

Thanks

Steve

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Online glarsson

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Re: Help with Rigol DS4014E on 10MHz external ref
« Reply #2 on: February 04, 2018, 06:55:34 am »
I tested the external sync on my DS4054.

* Connected 9.999MHz sine at 3.3Vpp to CH1.
   - Display shows nice sine wave.
   - Hardware counter shows 9.99903MHz.
   - As expected.
* Enabled external reference as input and connected the same 9.9MHz to external reference input.
   - Display shows attenuated and distorted signal. More a triangle wave than sine.
   - Hardware counter shows 9.99903MHz.
   - Not expected. Did not expect the reference input to distort its input. Expected the hardware counter to show 10.0000MHz.
* Disconnected the 9.999MHz signal.
   - Display shows no signal.
* Enabled external reference as output.
  - Display shows a distorted 10MHz square wave at 2.6Vpp. The distorsion of the square wave is similar to the distortion added when the external reference is an input.

So, the external input distorts the connected reference and does not lock to it. It can't even produce a clean reference output. Completely broken.
 

Online TurboTom

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Re: Help with Rigol DS4014E on 10MHz external ref
« Reply #3 on: February 04, 2018, 09:45:49 am »
I had similar doubts but found the external ref input to work (at least most of the time...). I'm using a +7dBm, transformer coupled Rb source (no risk of ground loops). I found the internal reference of the oscilloscope (MSO4014 "+") to be quite jittery, so loooong trigger delays will result in difficulties to get a stable waveform. The DS1054Z and the DS2072 are much better in this regard. But as I connect the external reference, the waveform goes stable within a second or so. And that's not related to the signal source possibly being affected by an unstable external reference since the source was running off its (apparently quite decent) internal oscillator.

So yes, the external reference input is working (at least on my unit) but the scope doesn't notify of the reference source being used -- room for improvement!

I think all the rigol gear with external ref inputs check the signal for "plausibility" before it actually gets used.

Cheers and good luck,

Thomas

 

Offline picitup

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Re: Help with Rigol DS4014E on 10MHz external ref
« Reply #4 on: February 04, 2018, 08:29:40 pm »
Hi Both

Thanks for taking the time to try it out :-)

@glarsson it sounds like your input does work, but not properly.  On yours if you disconnect the ref clock in you lose display which is expected and on mine, the display works just fine with the ref clock disconnected.

I didn't think of connecting the 10MHz output to a channel, but just tried this.  The result is a slightly grubby square wave at 10MHz at 1v pp which is a bit low, I think.  Also the frequency label from the left menu dances around between 9.996 and 10.04 MHZ which is a bit weird if it all comes from the same timebase.

@TurboTom thanks for the info.  Yes I agree there should be an icon on screen but I think I might know why there isn't.....

Probably cynical but I think they've had a problem with the design and what they have done with my scope is make the ref input inactive, just connected to the internal timebase and an icon would show that you weren't connected.  Given the background and poor documentation and extracting info from Rigol about the electrical specs implies to me they know there is an issue.

I wonder how many users think they are running ext ref input when actually they are running internal timebase.

I'll give them a call tomorrow.  I don't want to send it back, but hope they can fix it.  See if I can get them to confess.  I'll report back what their response is.

Cheers

Steve
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Offline picitup

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Re: Help with Rigol DS4014E on 10MHz external ref
« Reply #5 on: February 05, 2018, 01:19:20 am »
Just another quick test.  I connected the clock output the ds4014e to my TF930 counter which in turned is clocked with the gpsdo.

The output at 10MHz was 5Hz high so 0.5ppm.  I had expected a little better.  Does anyone know what kind of xtal is in the scope?  Is it possible to do a closed case calibration? It doesn't seem good enough for an OCXO.

Cheers

Steve
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Online TurboTom

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Re: Help with Rigol DS4014E on 10MHz external ref
« Reply #6 on: February 05, 2018, 04:16:55 am »
The DS/MSO doesn't utilize an ovenized oscillator, at best it's temperature compensated (TCXO). I just did some tests with my MSO4000 and only can confirm that the internal reference is crap. Mine is also running high by slightly more than 5Hz but what's even worse is the jitter. Please see the photos of my HP53310A's MDA analyzing the MSO4000 Ref Out signal. The MDA received its reference from my Rb standard so compared to the oscilloscope, this could be considered spot-on.

This reference jitter of the MSO4000 manifests itself as an unstable trace when running the scope with delayed timebase. To visualize this, I attached two more photos (sorry, didn't have a thumb drive handy in the basement to take a"proper" screenshot so I just used the cell phone camera...), both taken with trace persistance set to infinite so all the "jittery" traces remain visible, the 10MHz reference output of the MDA (this time free-running, i.e. not sync'd to the Rb source) used as input signal to the 1st channel of the oscilloscope and the timebase delayed by 100ms. The first photo is taken using the scope's internal reference, the second using the external Rb reference.

One peculiarity is that at least my MSO4000 wouldn't properly lock on the external reference if I first select the EXT REF connector (->Utility->PG_Dwn->REF...) to operate as an input and then connect the source; it's got to be the other way round instead, first connect the stabilized source and then switch the EXT REF connector from output to input.

Seems like Rigol thought that nobody would ever use the external reference connector on a scope... anyway, there's no reason for using such a piss-poor reference source in one of their more expensive scope models, as I already mentioned before, both the DS1000Z and the DS2000A ranges perform way better in these regards.

Cheers,
Thomas
 

Online jjoonathan

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Re: Help with Rigol DS4014E on 10MHz external ref
« Reply #7 on: February 05, 2018, 07:41:33 am »
Here's a picture of the DS4k crystal looking a bit small for its pads: https://photos.app.goo.gl/cWrb1mVaAugpCG7Q2

Also, the 1GHz ADC clock lines are unterminated and largely floating. There's a lot of common mode noise, but I'm not sure how much that affects the jitter in practice. Maybe the internal 10MHz is bad enough that it doesn't make things appreciably worse  ::)

Full album: https://goo.gl/photos/dxU3ChWUcvCMDW4N9
« Last Edit: February 05, 2018, 07:44:32 am by jjoonathan »
 

Offline picitup

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Re: Help with Rigol DS4014E on 10MHz external ref
« Reply #8 on: February 05, 2018, 07:53:59 pm »
Hi Both

@TurboTom thanks for all the tests.  Yes the jitter is crazy.  So it looks like the internal clock is crap and the external clock doesn't work.  More on this below.....

@jjoonathan thanks for the piccy.  Yes that's certainly no OCXO although for my machine 0.5ppm isn't too bad although a bit worse than I might have expected for the price of the unit.

Well...  I called Rigol in Germany and now I'm pretty pissed.  The guy in tech support told me that the external 10MHz isn't used for the timebase, but it acts as a phase adjustment to phase synchronise different devices.  I told him about my test of varying the input frequency and he confirmed that test would make no difference.

He confirmed there is no icon on screen to show the scope is using the external reference so I asked him how you can test if it's working.  He says he has a pdf which he will email me and I'll post it up here if anyone else wants to play with it.

Did I mention I'm pissed?  I spent ages looking for a scope of this calibre with an external 10MHz ref and it doesn't work in the way I expected.  I might return it but then will have to start searching again.

Here's the info from the latest user guide:

Quote
This oscilloscope can output the internal 10 MHz sample clock signal from the [10MHz In/Out] connector at the rear panel as well as receive an external 10 MHz clock signal from the connector. This function can be used to synchronize multiple oscilloscopes. Press Utility and press RefClock to select the desired clock type.

ClockOutput: output the internal 10 MHz clock signal of the oscilloscope from the [10MHz In/Out] connector at the rear panel.

ClockInput: the oscilloscope receives the external 10 MHz clock signal from the [10MHz In/Out] connector at the rear panel.

I suppose it doesn't specifically say it controls the timebase, but it doesn't say not either.  Have I been naive here or would others assume it would control the timebase?

Bummer.  Bummer. Bummer.

Cheers

Steve
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Offline picitup

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Re: Help with Rigol DS4014E on 10MHz external ref
« Reply #9 on: February 05, 2018, 08:44:09 pm »
I Have to go out now, but the pdf has arrived so here it is.

Cheers

Steve
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Online TurboTom

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Re: Help with Rigol DS4014E on 10MHz external ref
« Reply #10 on: February 06, 2018, 01:30:14 am »
Steve -

the external reference input works (almost) as intended - at least on my MSO4014(+). I rather think that the internal reference isn't working properly, at least on my "4000". The problem very much looks like the early PLL configuration "oopsies" that Rigol messed up on the DS2000 and DS1000Z series and corrected by firmware update some time later. Yet, with the proper sequence of applying the external reference signal and configuring the 'scope, it locks perfectly stable on the external signal.

I tried to explain the procedure how to identify and correct the problem before but probably my contribution was a little bit confusing...

So here's a short video clip that I recorded today to show the behavior of my 'scope with internal and external reference. I would be glad if others could confirm or negate if their "4000's" show the same problem. Please be aware that to reproduce the problem, a decent, low-jitter frequency source (preferably in the 10MHz range) needs to be connected to the input and the 'scope's timebase has to be delayed by a long time compared to the period of the input signal -- I set the delay to 100ms.

Video: http://www.turbinemuseum.de/files/MSO4000_Clock_Jitter.mp4

I also reversed input and reference source in order to find out within what frequency range the 'scope's PLL will lock -- my specimen does so within a range of 10.0MHz -50Hz +200Hz.

I hope this clarifies what I was trying to tell in my previous posts.

Cheers,
Thomas
 

Offline picitup

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Re: Help with Rigol DS4014E on 10MHz external ref
« Reply #11 on: February 07, 2018, 02:12:09 am »
Hi Thomas

Thanks very much for the video - I'm sure your explanation was fine, just me being dense  :scared:

I ran your test and got the same results.  Initially my trace showed heavy jitter and if I chose RefClock as ClockOutput and then ClockInput, the trace lost its jitter as it locked.  If then disconnect the RefClock input, the jitter comes back as expected, but if you plug the cable back in again, it has no effect until you cycle ClockOutput/ClockInput.

Funnily enough, when doing the second test for the PLL, when reducing the frequency, if I went too far and it lost lock, I could simply increase the frequency and it would lock again as expected.  However, when I increased the refclock frequency, when I went too high, it lost lock and would not recover by lowering the frequency.  This time it required a ClockOutput/ClockInput cycle to recover.

To answer your question, when experimenting with RefClock frequencies mine would lock successfully at 10MHz -63Hz + 254Hz so is a little more forgiving than yours.

I'll have a play with the Rigol procedure later.

Cheers Steve
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Offline picitup

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Re: Help with Rigol DS4014E on 10MHz external ref
« Reply #12 on: February 07, 2018, 02:43:47 am »
OK I just tried the Rigol procedure in the PDF above.  The procedure works if you start with ClockOutput and switch to ClockInput.  You can see the trace slide along to be in sync.

However, if you start with ClockInput, it does not work.  If you then switch to ClockOutput then ClockInput it works.  If you then switch the sig gen output off, it loses sync as expected, but switching the sig gen output back does not repair the loss of sync.  To make it work, you have to cycle the clock out/in then it slides back into sync.

I tried a few different voltage measurements from 1 - 3.9 vpp and square an sine wave, but all worked in the same weird fashion.

In the guide it says within 6 seconds you should get a lock.  I waited 30 seconds and nada.

I'm going to reply to the tech support guy and see what he says.  They must be aware of this!

Cheers

Steve
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Online rsjsouza

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Re: Help with Rigol DS4014E on 10MHz external ref
« Reply #13 on: February 07, 2018, 05:57:29 am »
Thomas, I was able to reproduce the jitter with a long timebase delay, but I don't have a precise 10MHz sinewave generator to compare. In my case, delays as short as 50us started to show a perceptible jitter. I suspect that is why my oscilloscope starts to fail decoding at larger streams (IIRC 200 or 500ms timebase).

One detail that I was curious: have you ever seen a low/mid end oscilloscope with an OCXO? (no, that does not excuse Rigol from having such jittery timebase)

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Online TurboTom

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Re: Help with Rigol DS4014E on 10MHz external ref
« Reply #14 on: February 07, 2018, 11:39:45 pm »
You don't need a sine wave for doing these tests, a square wave signal will also do. Moreover, most cheap TTL / CMOS XTAL oscillators will do for testing, so you may possibly find something suitable in your "salvage box", at least for jitter testing. If you want to try to sync your o'scope on an external reference, of yourse you will need a fairly accurate 10MHz oscillator since the catch range is rather small as figured out by Steve and myself. But once again, if you're lucky, you may be okay with a 50 cents CMOS oscillator that happens to be running close to the center of its tolerance range.

I have never seen a 'scope with an OCXO, the best that it gets seems to be a TCXO. Oscilloscopes aren't meant for highly accurate time/frequency measurements and also the protocol decoders should be fairly tolerant to slight frequency errors or jitter. I'm really curious what Rigol got wrong in the DS4000 since even the most basic digital oscillator brick appears to produce way less jitter than this 'scope's timebase. I've got the impression that it's the same erroneous PLL configuration that caused the jitter on the DS2000 and DS1000Z, only that it hasn't been addressed yet. Shame on Rigol!

Cheers,
Thomas
 

Offline picitup

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Re: Help with Rigol DS4014E on 10MHz external ref
« Reply #15 on: February 07, 2018, 11:50:10 pm »
Hi Thomas I've been trying to work out what the implications of a phase lock are vs an external timebase input.  I know if it was an external timebase input, the frequency would be as accurate as my gpsdo, but for the phase lock - would that change the frequency of the timebase or just align a leading or trailing edge of the timebase.

What I'm asking is with a phase lock, would the timebase frequency be the same as the gpsdo?

Hope this makes sense lol

Cheers

Steve
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Offline picitup

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Re: Help with Rigol DS4014E on 10MHz external ref
« Reply #16 on: February 08, 2018, 12:41:49 am »
Just a quick update on this.  I took a couple of screenshots, one of the 10Mhz gpsdo with the scope's internal timebase and then phase locked on the ExtRef.

I think my jitter may be worse than yours!  I'm going to post Rigol an old 555 timer I found on the floor in the shed and suggest they improve the timebase design  >:D

Any road up, I'll send them an email now and report the issues with syncing to an external clock and the jitter and see what they say.

Cheers

Steve
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Offline picitup

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Re: Help with Rigol DS4014E on 10MHz external ref
« Reply #17 on: February 08, 2018, 01:05:41 am »
Sorry but I couldn't resist this...

I realised you don't need an icon on screen to determine when it's in sync.  If there's not 3 yards of jitter it's in sync  :-DD

Keep Smilin'

Steve
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Offline Performa01

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Re: Help with Rigol DS4014E on 10MHz external ref
« Reply #18 on: February 08, 2018, 02:55:39 am »
The jitter looks spectacular in this setup, but do you really think a peak to peak jitter 0.2ppm of the delay time is that bad for a synthesized clock with a TCXO as reference?

From my experience, phase noise of a TCXO can be up to 40dB worse than a good OCXO for frequencies <100Hz distance from the carrier.

I would be really curious to see what you get when you actually phase-lock the DSO to a cheap external CMOS XTAL-oscillator.

 

Online TurboTom

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Re: Help with Rigol DS4014E on 10MHz external ref
« Reply #19 on: February 08, 2018, 08:15:25 am »
Actually, I did it the other way round, locked my MSO4000 (EXT REF) to my Rb source and connected some salvaged TTL or CMOS XTAL oscillators (the old ones in the metal cans with DIL14 footprint and only pins 1, 7, 8 and 14 populated). I supplied the oscillators with 5V from my bench supply through 1.2m long alligator leads and no local decoupling (cannot get worse than this...). Frequencies that I tried were 60MHz, 20MHz and 16MHz (no 10MHz to be found in my "collection" and I didn't want to experiment with the "odd" ones...). Those three oscillators didn't produce any jitter like seen with the unstable PLL (TB delay 100ms). Of course, there was some sweeping visible while the oscillators heated up, but this was well-defined and came slowly to a rest as the oscillators reached thermal equilibrium. If I had found a 10MHz oscillator, I would have tried it at the REF input as well.

I guess the REF oscillator inside the Rigol 4000 series isn't that bad, it's got to be the PLL that's not properly set up to lock. You get the same jitter with a good external reference if the reference is connected after configuring the oscilloscope to use the external REF input. Yet, even if one proceeds in this sequence, the external reference has some effect on the timebase (a "jittery phase shift" can be observed in the signal displayed), it just doesn't stabilize.

And yes, both DS2000 and DS1000Z perform substantially better than 0.2ppm jitter in reference to the delay time.

Cheers,
Thomas
 

Offline Performa01

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Re: Help with Rigol DS4014E on 10MHz external ref
« Reply #20 on: February 08, 2018, 10:44:04 am »
I guess the REF oscillator inside the Rigol 4000 series isn't that bad, it's got to be the PLL that's not properly set up to lock. You get the same jitter with a good external reference if the reference is connected after configuring the oscilloscope to use the external REF input. Yet, even if one proceeds in this sequence, the external reference has some effect on the timebase (a "jittery phase shift" can be observed in the signal displayed), it just doesn't stabilize.

Thank you for the test. I am still wondering what's actually going on here. You think the TCXO is fine but the PLL refuses to lock properly. But…
  • If the PLL is locked to the external reference clock, the jitter is gone. This proves the PLL works fine, once it's locked, doesn't it?
  • If the scope works on internal reference, the jitter is there. From the conclusion above, we have to assume the PLL to be okay and you also think the internal TCXO is fine, so what's left? The PLL not locking properly on the internal reference? If so, why would it reliably lock on an external reference (after switching from int. to ext.) but never on the internal one (after switching from ext. to int.)?
 

Online 2N3055

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Re: Help with Rigol DS4014E on 10MHz external ref
« Reply #21 on: February 08, 2018, 10:54:40 am »
I would rather speculate that PLL is fine, but there is some interference coupling into internal TCXO (basically FM modulation) or directly into clock signal on it's way to PLL... External signal might go different route and might avoid external signal coupling and won't have modulation being stable by itself...
 

Online TurboTom

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Re: Help with Rigol DS4014E on 10MHz external ref
« Reply #22 on: February 08, 2018, 11:46:26 am »
The real peculiarity is that if the PLL locks on the external reference depends on the sequence of application of the external REF signal and enabling the external REF BNC as input.

1. External Oscillator on / connected
2. Switch BNC to REF input
-- Does Work

1. Switch BNC to REF input while the external oscillator is switched off or disconnected
2. Switch on / connect external Oscillator
-- Does NOT Work

What this means for the internal reference oscillator is something still left to find out. I think there's a good chance that the internal oscillator itself is okay. I guess I've got to disassemble the oscilloscope and do some testing with my spare scope and the SA to find out what's really going on. I'm only worried since my MSO4000 is equipped with the single big heat sink that covers all the digital circuitry. Without removing it, I cannot access the relevant areas of the PCB. If I remove it and operate the scope, I risk overheating and damaging the ADCs / FPGAs.

Cheers,
Thomas

 
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Offline picitup

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Re: Help with Rigol DS4014E on 10MHz external ref
« Reply #23 on: February 08, 2018, 11:20:51 pm »
Thanks to all for your replies.  As usual, I'm learning loads :-)

Just for interest I've ordered a 10Mhz xtal oscillator from eBay for £2.98 item 400529955213 so I'll give it a bash when it arrives and report back.

No reply from Rigol yet, but it's only been a day.  I'm away for a few days now but will try and log in.  Here's the email I sent yesterday:

Quote
Hi Christian

I hope you are well.  Thank you for the document.  It took me a long time to get working due to an issue with getting  the scope to sync with an external source.  The issue is as follows:

If you select Utility/RefClock/ClockInput and connect the external reference it does not work.  I tried 1v - 3.9vpp sine and square waves.  If you then select ClockOutput and then ClockInput it works and the scope is in sync.

If you then turn external reference off, you lose sync as expected.   Then turn the ext ref back on and the scope does not sync.  To get it to sync again, you have to cycle ClockOutput/ClockInput with the external ref connected.  Any interruption in the ext ref breaks the sync and can only be repaired by cycling as mentioned above.

The second issue I've come up with is a *HUGE* amount of jitter.  I set the delay to 100mS and the screen persistence to infinite and took a screen shot.  Then I synced up the scope with an ext ref and the jitter disappeared (see pictures).

I'm assuming these are firmware bugs.  I did try to download the latest firmware, but it was dated 2016 and I bought the scope in October last year with the latest firmware.  My scope details are:

Model: DS40142
Serial: ********
Software: 00.02.03
Hardware: 1.3

I'd be grateful if you could let me know if you have a fix for these 2 issues.  Also, an icon of some kind on screen to show sync is achieved would be very helpful, otherwise it's a lot of guessing.

Kind Regards

Steve

Pictures are in previous post :-)
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Offline picitup

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Re: Help with Rigol DS4014E on 10MHz external ref
« Reply #24 on: February 10, 2018, 11:30:13 pm »
Well here's the reply from Rigol

Quote
Hi Steve,

please set the scope to normal trigger.

Christian

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