Author Topic: DG4000 - a firmware investigation  (Read 161775 times)

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Offline TurboTom

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Re: DG4000 - a firmware investigation
« Reply #450 on: October 26, 2020, 07:15:53 pm »
I guess I got lucky with mine... It started live as a DG4102.  >:D

 

Offline bgm370

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Re: DG4000 - a firmware investigation
« Reply #451 on: October 26, 2020, 07:35:23 pm »
I had the same calibration problem with my 4062 “enhanced” to a 4202 a while ago. Both 1.12 and 1.14 were not calibrating properly. I downgraded to 1.08 (it might have been an even earlier fw version) and it calibrated just fine. Then I upgraded it back to 1.14 and the proper calibration was preserved.
 
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Offline ralphrmartin

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Re: DG4000 - a firmware investigation
« Reply #452 on: October 26, 2020, 09:04:59 pm »
BGM, your suggestion certainly helped, although there's still something not quite right.
I now get a more-or-less flattish trace out to 100 MHz, and while I dont get so many weird jumps up and down now below 30MHz, I still get one jump down of about 0.8dB at 12 MHz or so.
There is then a linear-ish ramp down from about 100MHz to 200MHz, dropping a further 5dB.

I'm not too worried about the latter - perhaps the device just has some default values for this frequency range which wouldn't have needed factory calibration anyway.

However, the step at 12 MHz is rather more puzzling as I would have thought that would have been calibrated out.

On the other hand, the device is 7 or 8 years old now, so perhaps it has just drifted away from the original calibration.

PA0PBZ, I see if you look carefully, your plot also seems to show a bit of a drop at around 12MHz.

Perhaps I'll try to run through the full calibration procedure - but for both channels that seems to involve taking perhaps 300 power and voltage readings, and typing them in, which will be no fun when the DG's keyboard suffers from key bounce.

Thanks again for all the help.
« Last Edit: October 26, 2020, 09:06:46 pm by ralphrmartin »
 

Offline ralphrmartin

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Re: DG4000 - a firmware investigation
« Reply #453 on: October 27, 2020, 03:45:32 pm »
Well, having gone back to 4.08, done the calibration with defaults, and got a not too bad trace, and come back to 4.12, I then spent a morning doing a proper calibration (with multimeter and spectrum analyzer). The net result is back to like that shown in my original sweep: several serious jumps of a few dB up to about 12MHz, flat-ish out to about 100MHz, and then a linear-ish slope losing 4dB by 200MHz. Where it's flat and linear are probably flatter and more linear than before - but the large artefacts, and slope, still exist.

I suspect the slope might be due to different circuitry in the (newer?) higher frequency models.

However, if I do a sweep not from 1Mhz to 200MHz, but from 1MHz to 12MHz, all the jumps go away. So, they are not a calibration issue, but some sort of artefact produced by the sweep function,. Different ranges of sweeps make jumps in different places. Ugly.
« Last Edit: October 27, 2020, 03:49:00 pm by ralphrmartin »
 

Offline tv84

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Re: DG4000 - a firmware investigation
« Reply #454 on: October 27, 2020, 03:56:10 pm »
Let's call it a 30-100MHz model...
 

Offline ralphrmartin

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Re: DG4000 - a firmware investigation
« Reply #455 on: October 27, 2020, 04:37:48 pm »
Haha. Gained 40Mhz, lost 30Mhz, for an overall win by 10Mhz!  :-DD

But even stranger - if I set everything back to the factory calibration - all of the jumps disappear....
This sounds to me awfully like there's a "differencing two big numbers to get a small number" kind of problem somewhere in there.

So I now have a 0 MHz to 110MHz model ...  ;D
So apart from wasting a morning on a useless calibration,  I'm definitely winning!
And as long as I only want a narrow band at even higher frequencies, that's good too, as long as I check the exact output level separately.


 

Offline RoGeorge

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Re: DG4000 - a firmware investigation
« Reply #456 on: October 27, 2020, 04:51:33 pm »
I see no reason why it should jump like that.  Maybe the calibration instruments are not calibrated, or maybe the measuring setup has something wrong in it, maybe a cable is faulty, IDK, but my unlocked DG4102 doesn't show any amplitude jumps in the first 30MHz or so (also never touched its calibration - I suspect the altered calibration might be the most probable cause for seeing jumps).

Does the amplitudes and frequencies of the jumps preserve when a narrower frequency sweep is performed?

Offline ralphrmartin

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Re: DG4000 - a firmware investigation
« Reply #457 on: October 27, 2020, 05:37:21 pm »
It's the voltage settings (not RF power settings) which caused the jumps, and that was done with a 6.5 digit Agilent meter I've no reason to suspect to be out of spec. BNC coax lead to a BNC-banana plug splitter. Same coax lead to BNC-to-N adapter for spectrum analyzer. No problems with these leads etc in other work.

I've tried calibrating twice now, and both times ended up with jumps, once before going back to firmware 08 and redoing things there, and once after coming back to the latest fw.

Note that my machine doesn't show any jumps if you reset to the factory calibration.

Maybe the calibration procedure itself has some issues. It would be interesting to know if anyone has successfully recalibrated their DG4000 with the procedure given, with the current fw.
 

Offline RoGeorge

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Re: DG4000 - a firmware investigation
« Reply #458 on: October 27, 2020, 05:51:39 pm »
Does the same Agilent voltmeter shows the generated voltage (after calibration) as correct (constant) when tested at various fixed frequencies?  If not, then the calibration procedure went wrong.  If yes, then it's either the voltmeter or the spectrum analyzer.

Voltage jumps of 3 or 6 dB should be easy to spot on any instrument.  Does the jumps show on other instruments, too, e.g. an oscilloscope or some other less precise voltmeter?
 
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Offline ralphrmartin

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Re: DG4000 - a firmware investigation
« Reply #459 on: October 27, 2020, 06:43:01 pm »
Thanks for your comment, RoGeorge.

Does the same Agilent voltmeter shows the generated voltage (after calibration) as correct (constant) when tested at various fixed frequencies? If not, then the calibration procedure went wrong.

True (as long as I use frequencies within the meter's AC range), but that doesn't tell us where it went wrong:
- voltmeter not working correctly (e.g. giving inconsistent readings at different frequencies)
- I misapplied the calibration procedure (failed to write some values, entered incorrect values by mistyping for example)
- there's a bug in the user calibration procedure code e.g. it
-- tries to measure voltages at frequencies outside the DMMs capabilities
-- does something wrong with the entered values (stores them in the wrong place, wrong format, etc)

If yes, then it's either the voltmeter or the spectrum analyzer.

Not necessarily. The software in the DG4000 in general, and the sweep function in particular, may make some assumptions about the calibration. It is certainly doing something strange when sweeping, as the jumps may or may not be present depending on exactly what frequency range you sweep. Intuitively, miscalibration should always lead to the same voltage at the same frequency, just the wrong voltage, and that is not happens. The voltage you get at a particular frequency depends on the frequency range of the sweep.

Unfortunately, because of the jumps, I reset it to the factory calibration (which doesn't have them), so I have now way of telling which of these possibilities it is, without wasting another 1/2 day to redo the calibration. Note that lack of jumps observed with the factory calibration indicates that the jumps are real in my calibration (you said to see if they exist using a different instrument).

Furthermore, the factory calibration does give readings on the voltmeter (using the same leads) from 1kHz to 100kHz (in steps of 1kHz) which are within 0.2% or better of the stated output of the DG4000, so I have no reason to think the voltmeter is playing up.

Perhaps the software makes some assumptions about the entered calibration values, and if the calibration values entered are too far from the expected ones, it breaks these assumptions
« Last Edit: October 27, 2020, 06:49:30 pm by ralphrmartin »
 


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