Issue with Optical DisplayPort cable and L1 KVM

I’m planning to put my PC’s in a garage server room and running long cables to my office (to get rid of the heat and noise). To test I got a 30m DP 1.4 active optical DP 1.4 cable.

I’ve tested this from my Windows PC to a monitor and it works as you’d expect. However when I connect it to the KVM, there’s no picture.

Any ideas what could be the cause of this, and if there’s solutions (other cables for example) to fix it? I am hoping to connect a total of 6 monitors using these. Although it would be cheaper, and easier, to run the KVM in the garage, I’m having issues with actually being able to change displays with my keyboard, and obviously running to the garage wouldn’t be very convenient.

I have the 4-port, dual-monitor DP 1.2 Switch from L1.

This is the cable I’ve tested with:

Think I figured out the issue - the cable requires power from the display port connection on both sides, and the KVM probably doesn’t provide it. Don’t think this is an issue that can be solved, so might have to look into the other option of running the KVM in the garage.

That requires functional input switching using keyboard shortcuts which I currently don’t have. Worse case, perhaps I can use an extra keyboard specifically for this off to the side somewhere.

most optical display port cables have small power wires in them to provide power to the other end if needed.

I know they are pricey but have you tried a different brand?

I dont have a L1T KVM but I have an IOGear (ATEN OEM) which has worked fine with both Monoprice and Cable Creation Optical display port cables.

I haven’t tried another brand. I got this one because it was relatively cheap (~$115+tax in Sweden). Also just got a response from their support email I sent earlier that confirms that it does need power delivery on the display side (it is a hybrid cable, so it definitely has copper and fiber, but not for power it seems.

On that note, keeping the KVM in the garage IS a cheaper solution in terms of cables since I’ll need just two DP cables, a USB3/2 cable (this is the pricy one, but I found one that does both) and probably a USB2-> fiber setup (this is surprisingly cheap).

I could probably get away with a USB3 over fiber only as well but then I’d have to make sure to plug in USB2 in a USB2 hub, and USB3 in a USB3 hub.

In either case, given that the cable does work as output, KVM->Monitor, this seems like the logical way forward. The main issue is that I currently do have an imac that would remain on the office side of things, so it would complicate things on that end a bit (I used to use a USB-only switch for k/m and change inputs on the monitors manually, and it wasn’t the end of the world)

USB 2.0 over copper is dirt cheap. You can get CATx converters for as little as $7 sometimes.

I didn’t even consider USB2 over copper. That’s certainly an option as well. I’ll have plenty of RJ45 between the two locations. I do hope to get fiber put in as well (new constructions so I really don’t see why that wouldn’t work).

I wish DP to fiber converter weren’t all priced at “ask us” (at least $1k I think) - that would be the most elegant with in-wall fiber.

If you do make sure you run empty conduit too. And run both Multimode and Single mode. I made the “mistake” of only running 24 strands of SM and naturally my USB 3.0 over fiber converters only work with MultiMode SFP’s (8.5gb no less)

I’m definitely doing conduit - and hopefully a pretty sizable one or multiple. Since the original plan was to run 6xDP, 3xUSB cables and all.

Question though, do you really need single mode at all? Single mode seems more like what’d you use for really long distances.

Fibbr brand fiber optic dp cables tested to work fine with the dp KVm.

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not really and difference in price tbh so why not? I have a mix of MM and SM in my (home)lab but I also need SM for specific video over fiber applications.

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I suppose it wouldn’t greatly hurt to get some installed, just in case. Don’t have any use case for it right now though.

Do you know which Fibbr cable(s) were tested? They have multiple models.

I have an Aztebe fiber optic displayport cable and I can confirm it does not work with the L1 KVM. I’d hate to buy and run another cable that won’t work with it.

Interesting. It was the only listing on Amazon at the time.

There is a directionality to the cables. Do you have the cable you have going in the right direction?

If its between the GPU and KVm it’ll get power from the GPU. If its between the KVM and monitor it’ll get power from the KVm. Those are also different situations and one may work vs the other. The KVm doenst have much sayso in it not working if it’s between gpu and KVm unless the output signal is so weak at the KVm it can’t push the signal through the KVm and another dp cable. (remember no repeater in the KVm).


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Hi Wendell!

Thanks for the prompt reply. The cable works fine plugged in direct between the GPU and the monitor, just not via the KVM. I unplugged the end that was in the monitor, and plugged that into the KVM. I tried a couple of ports, and I tried different DisplayPort cables between the KVM console port and monitor, but alas.

Since you mention the KVM is not a repeater, do you think it might work if I put a repeater in between the KVM and my fiber optic DisplayPort cable? Club3D makes a repeater which is around $20-$25.

It’s a case of garbage in, garbage out with a repeater.

Think about it this way: the KVm enables one long signal corridor from the GPU connector to the display. Each cord can work fine but if cable has no extra signal margin then it can’t push it through another 1-3 feet of cable.

From the GPU point of view it looks all the way down both wires. Both wires plus the KVm is the corridor the signal has to go down. There is some signal loss across the KVm and that’s normal.

A repeater is a worse problem because if it’s repeating a marginal signal from a marginal “works but barely because of the nature of digital signals” displayport cable AND you lose freesync/gsync compatibility. That’s why we didn’t put one in, in the first place.

Interesting. Thanks for the explanation.

Can you (or anyone else for that matter) point to a particular make and model of fiber optic displayport cable that is known to work with this KVM?

Not sure if it matters, but I’ve got this version of the KVM.

The one I mentioned before seems to still be sold by Amazon but the one I have is over a year old.

@wendell what do you think the chance would be newer Fibbr optical DP cables would not work where your year old ones does?

I have a Samsung Neo G8 on the way and currently have 2m Club3D 8K DP1.4 cable between my PC and KVM, and a 1m Club3D 8K DP 1.4 cable between the KVM and my monitor. Current monitor is only 1440p60 so it works fine with a 3m total cable length plus any losses due to the KVM.

I read of issues with the Samsung G9, so I’m concerned I may run into issues with the Neo G8 at 2160p120 and even more so when I upgrade my GPU to one that supports DSC for 2160p240. I can’t fix the distance issue easily so I was thinking of replacing the Club3D cables with Fibbr ones for this monitor.

What GPU do you have?

You might have to run 8 bit worst case scenario. The g9 issues are a bit overstated imho because only a few of them have problems once you get the firmware updated.

At the moment a 1080ti. Will probably replace when the next generation drops. Does AMD or nVidia behave best with the KVM?