Home        Store        Docs        Blog

600m tether length with advanved bluerov2 package

(Kelsey) #1

Hi all has anyone tried using 600m or more tether with the fathom x boards and had a reliable connection?
I have a customer that requires that length of tether to fly a pipeline.
From what i have read it should work in theory but im just wondering if anyone has tried it?

Also if possible @rjehangir could you supply a single length of tether that long?

Regards

DemonRobots

0 Likes

(Rusty) #2

Hi Kelsey,

We haven’t tested that but we can definitely supply at 600m tether. We currently get the tether on 1000m spools.

This is something we could test out here. I’d like to do that at some point.

EDIT 3/7/19: Obsolete information, please see below here.

-Rusty

1 Like

(Kelsey) #3

Hi rusty

That would be great if you could test that out for us.
If it worked on 1000m would be even better.

If you get a chance sometime soon could you try that for us please.

Thanks heaps.

Kelsey

0 Likes

(Luc) #4

Hi Kelsey and Rusty,

I recently made some tests with a simple telecom wire pair, 600m length.
( this one : http://www.alliedelec.com/rs-pro-411784/70791947/ )
The link was ok, with a continuous transfer rate of about 53Mbits/s ( tested with iperf )
I believe that with BR tether it would be about the same.

Hope this help…

1 Like

(Rusty) #5

Luc,

Awesome! That’s very helpful. I’ve also seen the bitrate drop off a bit at longer lengths. I saw 80 Mbps at 100 meters and 60 Mbps at 300 meters.

-Rusty

0 Likes

(Luc) #6

Rusty,

Yes, the FathomX has nice performances !
I’m currently trying to qualify it for a tether length of 1000 to 1500m.
But there are precautions to take to make such tests

The cable must be unwound
( try to disconnect one of the wire when testing with a wound cable, you’ll see that the link will still work ! )

Performances are differents in air and in water.
With the above telecom pair, once immersed (in fresh water !), the maximum length fall down to 290m, with a bitrate around 24 Mbit/s
I’m sure that with a cable with an outer jacket ( like BR tether )result should be far better, but this was intentional to test this “worst case”.

It would be nice to have informations about attenuation vs frequency for the BR tether.
Rusty, do you have such a graph ?

Luc.

1 Like

(Rusty) #7

Hi Luc,

Very interesting. I’m curious to try with the jacketed tether. We don’t have a plot of attenuation vs frequency but that would be useful.

-Rusty

0 Likes

(Rusty) #8

Hi all,

Just for reference, I performed a bandwidth test with 1000m of tether. The tether was wound on a spool and in air during this test.

The maximum bandwidth dropped to about 28 Mbps. That’s plenty for video and the connection remained clear. There was no additional latency on the video stream.

I do think the results could change if the tether was unspooled and/or underwater, so these results should be taken with caution for now.

-Rusty

1 Like

(ocenaman) #9

hi,Luc & everyone
How much can the Fathom X transfer when using 1000m tether?
20Mbps@1000m is OK?

@luc-rossi
@DemonRobots

0 Likes

(Luc) #10

Hi Oceanman,

unable to reply, i’ve not 1000m of tether at this time !
I did some bandwidth test with 150m ( in air ), but i need to make the same tests in water to check for the differences.
I’ll post the results as soon as i have enough time to perform this test !

Luc.

0 Likes

(ocenaman) #11

OK,Thank you very much
I guess that It also depends on ,maybe,the quality of cable

0 Likes

(achat) #12

Hi Luc,

Any new about your testing over long distance cable?

0 Likes

(Luc) #13

Hi,
sorry, I haven’t tested more than 300m of BR tether yet !
But the good news is that the bandwidth is about the same in air and in water!

I also tested 300m of BR slim tether in water and found about the same performances that with 4 pairs BR tether
( about 70Mb/s )

0 Likes

#14

I just found this post from Rusty in 2017 about 28mbps @ 1000m and was wondering if more testing had been done unspooled in water? Did the performance decrease while transitioning from Rev1 to Rev3 tether?

Was trying to order the max slim for the big spool (540m) and this is what BR sales came back with…

“We can sell the slim tether at longer lengths, but we have communication issues using our Fathom interface boards. If you have a different method for communication, then you should not see any issues.”

“The home plug spec is not accurate for this type of tether construction. 200m is the reliable maximum for slim and 300m is the reliable maximum for standard tether. Bandwidth drops to unusable levels above these lengths.”

“Our engineers think it’s a combination of impedance, capacitance, and resistance that determines the bandwidth capability of a tether. Additional shielding will not help in this case.”

Can anyone provide some clarity on their real world experiences using either slim or standard at 500m+?

Anyone know why the standard may be 1/3 better?

0 Likes

(Marcus) #15

There was a report in Australia this week of a unit rescued trying to perform a pipeline inspection losing comms somewhere at the 600m mark-so based on that I would suggest it’s not reliable. Trying to stretch the specs that far is risky

0 Likes

#16

I don’t know what was conveyed and if the risk was accepted by the client, so I won’t judge in that regard. Still, it’s a good sign that it was working, at least long enough to get in there. I wonder if they dropped the video quality and what tether they were using…

0 Likes

(Kelsey) #17

We had a client that went 750m successfully with the copper setup. Like Marcus says it is risky though. The temperature of the environment seemed to make a huge difference to the bandwidth. They also experimented twisting different combinations of twisted pairs together in the tether. I think they were lucky not to loose comms as there are so many variables. We recommended that they go down the fiber optic route due to the risk but they pulled it off.

0 Likes

#18

I’d reeeeeaaaaally like to hit 500m depth, plus a couple/few meters for going over the boat and however much should remain on the spool for strength. The large spool is supposed hold 540m of slim tether, so maybe 510m-520m if trying to keep it as short as possible. From some of what I’ve read, I feel like it’d probably work at 520m if it were standard tether and I’d be willing to take the risk, but if the slim really is 33% worse than the standard, then maybe not. Was hoping Rusty would chime in with some real world comments about the slim. I don’t need the “we can only officially recommend…” thing, I get that, just looking for the “you’re on your own, but…” comment.

The bandwidth is just about all video, so do you know if they had to drop the video quality down to get 750m and what tether they used?

0 Likes

(Kelsey) #19

They used the bluerobotics Revision 2, 7.6mm fathom tether with the standard video settings.
Use all the conductors in the tether, 2 twisted pairs each for positive and negative.

0 Likes

(Etienne Demers) #20

I think that once you start going to these depths and cable length its no longer in the realm of hobby ROV and investing more money on the system is mandatory.

I myself have switched to fiber and never going back to copper.

1 Like