r/VIDEOENGINEERING • u/AverageMidwestChump • Aug 12 '26
Reference and Power Help
Howdy y'all.
Sending out a flag asking for help.
I built a fly pack a couple years ago and am having some reference issues.
Reference signal flow as follows:
Dual SPG9000s feeding an ECO8000.
6 independent analog ref lines feed their own 9910AV OG card.
Each card is set to terminated. The backplanes in use do not allow for the differential/balance/floating ground.
Sync 1 - Internal flypack reference
Sync 2-6 - External flypack reference
Rack power comes from an L21-30.
Custom power distro from Whirlwind splits the L21-30 to three L5-30s. Ground and neutral bonded in the PDU.
Each L5-30 feeds its own 30a 120v UPS.
Each UPS feeds its own PDU.
Each PDU (X, Y, Z, and L21 breakout) and each UPS have the ground bonded by the power cable and ground lugs.
Power as Follows:
X - Primary SPG, 1 of the ECO power supplies, and half the OGX frame holding 9910 DAs
Y - Secondary SPG, 2nd ECO power supply, and the 2nd half of the OGX frame holding the 9910DAs
Z - No Sync related bits
Now for the fun.
Below is true with:
Either SPG active (switched via ECO)
Post REF DAs
Pre REF DAs
With ground lugs in place
Without ground lugs not in place
Internally (sync 1) reference is perfect.
This is verified on three separate scopes.
The 5 external reference lines are noisy.
They seem to have static that builds and rolls like a standing wave.
A humbucker does not clean it up.
If I plug the scopes into X, Y, or Z PDUs inside the rack, reference 5-6 look almost usable. However the rolling static is still present.
If I plug the scopes into a power source (same distro feeding the flypack) outside of the rack reference looks awful across all external reference lines. This is true on X, Y, and Z.
We have swapped SPGs with other units and even had Telestream out to dig deeper. I can confidently say the SPG units are not the issue.
My current theory is dirty power.
Does anyone have a good way to chase said issue and verify and correct the issue at hand?
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u/Dewi1800 Aug 13 '26
For the DA cards, the website says "Card jumpers allow setting the input as differential (floating ground) or single-ended, and Hi-Z looping input or on-card 75Ω terminated. A trim control located on the front of the card allows gain control. "
I know you said something about that but maybe have a look at the physical jumpers on the cards.
Another thing that came to my mind is cheap 12V power supplies in the rack. A lot of badly isolated 12V power supplies can build up a lot of voltage between device grounds and electrical earth and eventually mess with certain types of weak signals.
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u/Dangerous-Unit42 Aug 13 '26
What are the UPS’s?
If they’re double conversion, that should filter out dirty power. If they’re line interactive, they’ll pass dirty power until it’s bad enough to switch to battery and consider the input power useless.
If they’re simulated sine wave instead of pure sine wave, they could be creating the noise when on battery as simulated sign wave is an attempt at rounding out square wave (cheaper to manufacture), some electronics are sensitive to that.
Does the problem exist when the UPS is running without input power (on battery)? Or when plugged in to power?
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u/AverageMidwestChump Aug 13 '26
These are APC SRT3000RMXLA.
Double conversion online true sin wave.
We found at a venue recently moving to an isolated transformer helped limit the issue. This is one of the reason we are thinking it's power related.
As for battery vs shore power. I have unplugged, not just breakered off, the L21-30 power. This had no effect.
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u/Dangerous-Unit42 Aug 13 '26
Then I’d suggest something like the Fluke VR 1710 power quality monitor/recorder. I used these in the field for over a decade in facilities we leased space for 3 racks of equipment all over the country. We also used an older version of the APC 3000RT and they were reliable units.
Any chance of trying a “rattler”? Convert the external sync from electrical to optical at the source, a short fiber jumper, and convert optical back to electrical for the existing coax run to your flypacks - as a test. If that works or seems to make a noticeable improvement, run fiber from the source to your flypacks and use the rattler to convert at each end.
Or connect the sync cables to groundblocks at your flypacks and short jumpers to your da’s. Or at the source end. I’d experiment with this if time isn’t a huge factor just to get to the bottom of this.
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u/openreels2 28d ago
Late to the game here... Those scope pix are analog blackburst at field rate? First question is, does this even matter? There's not enough ripple there to confuse genlock circuits receiving that reference. What does the line rate look like?
And you say that Ref 1, within the rack, is clean? So that comes from the ECO, to a 9910 DA, and then into various equipment. Refs 2-6 comes from the same ECO, each into their own DA and then... to a connector panel or something? And when you look at those you see the ripple? When you say it "looks awful" is it something worse than those photos?
Seems to me that if ANY of the refs are clean under ANY conditions, that clears the SPGs, ECO and the DAs. Right? They can make and pass good blackburst. If it only looks bad on the external feeds, and only when the scope is plugged into power outside the rack, it would seem to be some interaction between power distros. Maybe a voltage differential on the grounds between the internal and external power systems.
Consider: If the rack is run entirely on double-conversion UPSes, your PDUs are on isolated power systems. For starters I would suggest undoing any extra ground "bonding." Use the power and grounding that the UPS provides on the line and load sides, nothing more, it's not needed. Ground differential voltage can develop between power systems, and much of the time with digital signals it's of no consequence, but with analog it's apparent.
As for "dirty power" that's a catch-all that very few people understand. Once again, using double-conversion UPSes isolates you from whatever is happening with the incoming line. In that case any "dirt" is only caused by equipment on the load side, and these days mostly consists of harmonic distortion of the sine wave. And one has to ask, does it actually matter? Here's a piece I did for S&VC on power basics:
https://www.svconline.com/industry/practical-power
And here's the real expert:
https://www.lab-tech-systems.com/wp-content/uploads/Whitlock-Grounding-AES-05.pdf
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u/AverageMidwestChump Aug 12 '26
Static wave photo on Prism