Products > Test Equipment
DG4000 - a firmware investigation
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bgm370:
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.
ralphrmartin:
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.
ralphrmartin:
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.
tv84:
Let's call it a 30-100MHz model...
ralphrmartin:
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.


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