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600m tether length with advanved bluerov2 package


(Adam) #21

Hi @corndog,

I’m not sure what answer you are looking for, but the numbers are pretty straightforward:

  • The maximum reliable communications distance over the Fathom tether is 300 m with the Fathom X
  • The maximum reliable communications distance over the Fathom Slim tether is 200 m with the Fathom X

Beyond these lengths, we found our current system becomes unreliable, with bandwidth going off a cliff, communications constantly going in and out, and packets dropping. The difference between working fine and not working at all can be as little as a few meters. We believe the difference is down to the specific properties of the cables, inducing resistance, capacitance, inductance, and overall frequency response. This is what Elisa relayed to you from me.

The homeplug communications standard is no easy task to unravel, as it uses a whole swath of frequencies from 2Hz-28mHz. Unfortunately we can’t really give you an “you’re on your own, but…” comment, as we’re still figuring this out ourselves. However, we are working on it and currently taking a deep dive into the standard and nitty-gritty details of how this communication works, moving towards hopefully raising this current limit. If you want to go beyond our existing ratings you are welcome to do so, but you are truly on your own and in the same boat we are currently in.

At this point to only reliable method to significantly extend tether range is to go with fiber or perhaps switch to serial communication with analog video.

-Adam


#22

Well the answers I’m looking for would be everything in the last 24hrs with a question mark, but what changed between Rusty’s post and BR’s current straightforward numbers? Things seem to be going backwards. Did BR find that when it was unspooled in water that things got worse? Was the older tether better than the newer tether in terms of bandwidth? All I’m looking for is more information to fill the gaps between these data points, to see how we got from there to here. Maybe it’s just the standard “businesses trying to play it safe to protect themselves and keep customers happy” kind of thing, I can’t tell, just trying to figure it out because what I want to do exceeds the recommendations.


(Etienne Demers) #23

Not sure what Bluerobotics tests came out with but I remember that the old tether and communication setup would work fine with 300m. The last ROV I got for a client with new tether and FXTI had really poor performances with lags on video etc.

I didn’t have much time to play with it and the system is now on a shelf at the client’s office until June when I am supposed to go do some onsite training so I hope to get better results and figure out the issue then.


(Adam) #24

Hi @corndog,

I apologize if my response there came out a bit brusque, that was not my intention at all! Upon re-reading I see that it could be taken that way, I was bit careless with my wording. My intention was to make my answer clear to everyone who comes across this thread now and in the future.

What changed was doing multiple thorough tests and spending countless hours on this question rather than a quick bench top test with a tether on a spool like Rusty originally did. We later learned that with tether coiled up, the signal can hop between coils and does not travel the full distance, at least in air. The tweaked construction of the tether may also be part of it, but this is the bulk of the explanation, we’re still figuring this our ourselves.

We aren’t in the habit of censoring previous answers or editing old posts as we want everything to be out in the open and available to the community. However, this thread does bring up an issue with our forum that we should probably address. Largely because we are a young and growing company, some of our older responses may not be accurate anymore. There is a lot of older information in buried threads like this that can be misleading given what we learned at a later date.

An open question to everyone in the thread here as to what we should do with posts like this:

Would you prefer that we edit our old responses that are obsolete or otherwise deprecated with links to more recent relevant and accurate information that has been developed over time with more experience/work? Should we delete the original content, or just add a note at the bottom of the post? Or should we leave them alone altogether?

-Adam


#25

Oh no worries Adam, you’re all good!

That second paragraph is exactly what I was after, though I’d still like to know why the slim is rated lower? Not a big deal though, this all tells me I need to look at a fiber solution.

In my opinion, you couldn’t possibly keep track of everything said throughout the years, so when someone comes across info like I did and had more questions about it, it worked itself out and now all the information is contained in one spot for when someone else comes across it someday. It’s closed loop. And there’s good info in here, I wouldn’t delete anything.


(Adam) #26

Thanks for assurance!

The slim is rated to a shorter distance because it doesn’t perform as well as the standard and bandwidth goes off the aforementioned cliff earlier, leading to a 200 m rating rather than a 300 m rating. We believe this is down to differences in resistance, capacitance, inductance, and overall frequency response due to the different constructions. At long distances, homeplug communication appears to be particularly sensitive to some difficult to nail down cable properties that we are still in the process of understanding ourselves.

My main concern is the case when someone comes across old forum posts directly from a google search or with the forum search tool, and don’t make a post themselves. When something comes up organically like this thread and this discussion continues, it is less of a concern unless someone doesn’t read all the way down.

-Adam


#27

Yeah it would be nice to figure out exactly what’s needed to get closer to those Homeplug specs. Have you guys done any testing with the 500mbps version LX200V30?


(Etienne Demers) #28

Maybe you guys should consider using aluminum foil for your next tether:

image

This is how all commercial ROV tethers I came across have twisted pairs.


(Martin Herren) #29

Deleting is often a bad idea. Maybe adding a bold note on the top (and even bottom) post to mention that the thread is obsolete, and refer a new, to be created, thread.


(Adam) #30

We have tried the 500mbps version LX200V30 and performance is slightly improved, but not much. That module uses higher voltage (12 V), so a separate power supply or boost converter would need to be used topside, as 5 V USB power would not suffice. We decided against upgrading to it due to the minimal improvement and aforementioned additional complexity/drawbacks, we are working on other approaches. That is an option to try however if you are willing to tinker.

Shielding is something on our list to try as well.

-Adam