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Tether bandwith bad

After I completed the ROV I took it to a pool and everything worked fine. The tether was just in a open roll then and I had 90 up and 70 down speed with 80m tether. Now I put it on a cheap spool with a slipring and the bandwidth dropped to sub 2Mbps. I have been trying to figure this out for days now and it is driving me mad. Bypassing the slipring I get 10Mbps, resistance is where it should be around 10Ohms. When I connect directly with a short UTP I have no problems. First I thought it was the pigtail of the connector which is around 20cm un-twisted but it worked fine in the pool.

So my question is, if I get the Fathom-X will I increase the bandwidth of the single pair (now I use 2 pairs). If anybody knowledgeable could point me in any direction I would be grateful. Attaching a pic of the setup for reference. Maybe I should point out that I did upgrade the pix and the Pi software to the recent version, not that I think it matters.

Best, Joe

So lemme get this straight…

You were using all 4 twisted pairs without the Fathom X boards?

The FathomX boards will just turn 4-pair wire into 1-pair.

In the water the wire won’t have EMI issues, as the water blocks EM pretty good.

I don’t use a slipring at all, my spool works like a baling fishing reel, winding the tether onto the spool, not spinning the spool.

You could maybe try putting the whole spool inside a grounded metal or foil box. If everything was fine before putting it on the spool…

Thanks Darrell,

I am using 2 pairs as per 10/100 network standard (1,2,3,6) without the Fathom X board

Was not easy to find information on this, mainly since splicing and soldering UTP/STP cables seems to be a big no no. Took the tether to work where we have an IT section with measuring equipment and they found that the 3 splices (slipring, subcon connector in and out) caused the problem. After days of trying I singled out the Subcon to be the choke since (I thought) it has straight cables in the pigtail.

I now have 2 working pairs after trying many combinations and believe that it was Impedance bump at the solder joints and not so much cross talk that caused the problem. Of the 8 wires in the Subcon many combinations simply cancelled each other out but had continuity and proper resistance when measured (witch drove me mad). It seems that everything needs to be very precise, length of solder wires, amount of solder, the length of pigtail etc. For example, I measured 30 on the upload and then started to pinch and bend one pair at the solder joint and it went to 70?

Anyway, I have it working now and will roll the tether in the pelican case (works better for me)

Didn’t know about the EMI water block, tx.

Best, Joe

Is there any reason you’re not using a fathom board? The homeplug protocol is very forgiving in terms of conductors used/soldering etc.

That is the plan eventually since i have other ideas for the three remaining pairs, but when i upgrade to heavy.

Still l think its strange. I have pinpointed this problem to the subconn bulk head and can’t figure it out at all, the wires simply want let anything through but are connected. Was hoping someone came across this in the past.

I haven’t come across it before, but i can imagine it being a problem. Ethernet standard is only 80m max (I think, maybe 100m). Those are going to be based on ideal conditions and uninterrupted CAT5/6 cable. With your setup, you’ve got potential issues at the slipring (solder/straight cables), pigtail connection (solder), pigtail (straight cables), bulkhead connection (another interruption), and then from bulkhead to Pi ethernet port.

I’m confident using Homeplug (Fathom board) will solve your issues (and free up spare pairs) and offer more reliability (even once you have the system working in air, it’s possible you’ll find issues once the unit is submerged).


got the fathom x installed and damn what a difference. Problem solved thanks.