Video interferance
Re: Video interferance
REALLY just guessing here Ken, but maybe the baluns are not balancing things properly, or maybe one of the wires in the video pair is getting water into it?
Re: Video interferance
Hi Ross,
I almost sure it is not either of them, for I start I'm not using baluns at the moment as I saw no difference with or without them.
And the interference can be switched on and off like a switch just by putting the rov into or out of the water, it can even be just the light housing on the front (maybe it's them?).
I think it may be some sort of a ground loop issue, not that I have researched that but it sounds about right. It could also be that there are 3 different power supplies involved in the whole process, the Rov, the topside box and the boats. I may try to attach the topside box upto the boats cig socket to see if that somehow balances things out.
If I can get a daylight viewable screen going at a bargain price, I'll just forget about using the boat screen.
There is a guy on ebay selling replacement LED backlights for LCD panels, he claims with two of his drivers and strips I will get about 1000 NITS (cdm2).
This is a copy of his reply Sunlight readable from three feet requires about 800 ca/m^2. For a 13" diagonal-measure monitor you require 10.4" LED strip(s). If the display uses (2) edge backlights, you would get about 1,000 nits with our any-length kit. If your display uses only one back-light tube, you would need two LED driver boards and two 5.2" LED strips. Most LCD displays use a top and bottom edge back-light. I hope this helps. Thank you for your inquiry.
The only problem is that my LCD panel I have only has one strip, he says I can put 2 short ones in there, but I think it would washout the bottom the screen too much??
I almost sure it is not either of them, for I start I'm not using baluns at the moment as I saw no difference with or without them.
And the interference can be switched on and off like a switch just by putting the rov into or out of the water, it can even be just the light housing on the front (maybe it's them?).
I think it may be some sort of a ground loop issue, not that I have researched that but it sounds about right. It could also be that there are 3 different power supplies involved in the whole process, the Rov, the topside box and the boats. I may try to attach the topside box upto the boats cig socket to see if that somehow balances things out.
If I can get a daylight viewable screen going at a bargain price, I'll just forget about using the boat screen.
There is a guy on ebay selling replacement LED backlights for LCD panels, he claims with two of his drivers and strips I will get about 1000 NITS (cdm2).
This is a copy of his reply Sunlight readable from three feet requires about 800 ca/m^2. For a 13" diagonal-measure monitor you require 10.4" LED strip(s). If the display uses (2) edge backlights, you would get about 1,000 nits with our any-length kit. If your display uses only one back-light tube, you would need two LED driver boards and two 5.2" LED strips. Most LCD displays use a top and bottom edge back-light. I hope this helps. Thank you for your inquiry.
The only problem is that my LCD panel I have only has one strip, he says I can put 2 short ones in there, but I think it would washout the bottom the screen too much??
Re: Video interferance
I think you are on the right track thinking ground loop. Earlier I was going to suggest to try tilting the the outboard up out of the water, assuming your boat is outboard powered, glass not aluminium and asking if there were any other grounded fittings in contact with the water. The only other thing I'm thinking of would be to run the fish-finder display and topside box off a separate battery, with a separate or floating negative/ground, so it is not electrically connected to the boat. The transducer is probably small enough not to couple into the water, so you can still use it at the same time. Still not a proper or ideal fix, but an interesting experiment perhaps 
Putting the baluns back in may be a pain but could be the solution. It really is "not the done thing" although you have proven that under good conditions twisted pair and no baluns is OK. When other things come into the equation like conductive water and earth loops and potential sources of interference, baluns become important. Actually, you don't even need a water leak to form a path conductive to noise or any other non-steady-dc signal, all that wiring, even insulated, has capacitance so has the ability to pass signals/interference.
Putting the baluns back in may be a pain but could be the solution. It really is "not the done thing" although you have proven that under good conditions twisted pair and no baluns is OK. When other things come into the equation like conductive water and earth loops and potential sources of interference, baluns become important. Actually, you don't even need a water leak to form a path conductive to noise or any other non-steady-dc signal, all that wiring, even insulated, has capacitance so has the ability to pass signals/interference.
Re: Video interferance
I did try tilting the motor up but it is an Ali boat, regardless it didn't help.
My transducers (airmar SS264) are mounted thru the hull and have a stainless steel body on them, they may be earthed but shouldn't be. Unfortunately there is always an earth path to the hull with Ali boats though, the dealers I bought it from say that it can't be totally isolated, though I don't rely on the boat as an earth conductor at all. I think the starter motor has a lot to do with it.
I will put the Baluns back in, very simple job really, once I have the ROV open again.
Chipping away as always....
My transducers (airmar SS264) are mounted thru the hull and have a stainless steel body on them, they may be earthed but shouldn't be. Unfortunately there is always an earth path to the hull with Ali boats though, the dealers I bought it from say that it can't be totally isolated, though I don't rely on the boat as an earth conductor at all. I think the starter motor has a lot to do with it.
I will put the Baluns back in, very simple job really, once I have the ROV open again.
Chipping away as always....
Re: Video interferance
Hey Ken! Have you got this sorted out yet? I was wondering whether or not there is full-time comms on the tether, like even when motors are not being told to run? Do you have a ground wire in the tether that connects the MAX485s?
Re: Video interferance
Hi Ross,
Waiting a parts, as usual.
I'm using MAX488 chips for my data and no I don't have a ground wire connecting them.
My currently plan is to simply use a wireless av link to the sounder, as it's only the physical link that creates a problem. I'm sure there is an underlying cause as I had the two linked before without a problem, but for now I'm happy just to eliminate the cable between the two.
It's just a matter of time to get it out on the water, I am also working on tweeking some of the code to make better use of a LCD.
ken
Waiting a parts, as usual.
I'm using MAX488 chips for my data and no I don't have a ground wire connecting them.
My currently plan is to simply use a wireless av link to the sounder, as it's only the physical link that creates a problem. I'm sure there is an underlying cause as I had the two linked before without a problem, but for now I'm happy just to eliminate the cable between the two.
It's just a matter of time to get it out on the water, I am also working on tweeking some of the code to make better use of a LCD.
ken
Re: Video interferance
Cool.
Meant to say 488..... though the ground wire theory applies to both chips. FWIW, there is an isolated version of the 488 that uses optocouplers to overcome all but huge differences in ground potentials between each end.
By keeping the sounder/boat and ROV grounds separate with the wireless AV link (and a separate battery for the ROV controls), a ground wire in the tether is probably not needed. You have faced extra challenges due to the fact that the boat is aluminium and you are working in salt water. I would have to assume that most on the forum are in fresh water.
Looking forward to seeing what you do with the wireless link.
Meant to say 488..... though the ground wire theory applies to both chips. FWIW, there is an isolated version of the 488 that uses optocouplers to overcome all but huge differences in ground potentials between each end.
By keeping the sounder/boat and ROV grounds separate with the wireless AV link (and a separate battery for the ROV controls), a ground wire in the tether is probably not needed. You have faced extra challenges due to the fact that the boat is aluminium and you are working in salt water. I would have to assume that most on the forum are in fresh water.
Looking forward to seeing what you do with the wireless link.