splicing transducer cables

I just got off the phone with Eagle Electronics to ask them a couple of questions.  One was about how much power my unit drew so I could figure out the battery life with AA packs (seemed pretty short in practice, but I want to do the calculation) and more importantly, if I could splice the transducer cable.

The answer is yes, you can splice the transducer cable without effecting the function of the unit, so if you all want to do it, go for it.

(btw, my unit draws 350mA w/o the light and 750mA with the light on).

MolBasser

And why would you want to splice the transducer cable?

The only think I could think of would be to make it shorter.  I for one, don't like the extra 7 ft of transducer cable floating around me hull even though it's coiled up nicely.   I'm not sure it bothers me enough though to go through the pain of trying to splice it.

Brian

Yes, I am bothered by the long cable when I only need 1 foot.

I am pretty sure that I am going to splice it.

MolBasser

Sorta off topic but I was wondering if all that extra wire is forming a coil  creating magnet fields and causing interference when it collapses.

I think the cable is shielded-wrapped with foil. If I recall my 50's radio (tubes!) class, that cuts the field.   

I am sure thecoiled cables do create fields to some degree and the foil, if grounded whcih it probably is, will reduce them. I imagine the manufactures expect some of the cable to be coiled--after all if they tell you not to change the length and yet ship you one standard length, then of course it will be coiled to some degree.

Splicing the cable in not the problem, it is changing the length.

Sonar operates on a timing principle, the reflection of the signal is timed. Because the electronic time measuring cricuitry is in the 'head' then the total signal path being timed is: 1) 'electrical signal from head down the wire to transducer, 2) tranducer converts signal to wave and sends through medium (water), 3) refllection of wave received by transducer, 4) transducer sends electrilcal signal back up wire to 'head'. So anything that changes the propagation time from the calibrated time anywhere in this path changes the depth reading because it changes the round-trip time. That includes density changes in the medium (fresh or salt, warm or cold, etc.) and wire length. Manufacturers, striving for accuracy, often allow you to menu-select teh water as being either fresh or salt to preserve accuracy. Now of course electrical signals as very fast in copper wire and sound waves are much slower in water, so the percentage of the timing changed by altering the length of the electrical path (i.e. the wire) is probably a much small percentage of the whole path. But how much and of course it varies by water depth. I am sure I could figure out a formula to incorporate all the parameters and variable, but that's what I padi Humminbird for 

SOwithout devoting more of my time to gather data and analyze it (if we had more rainy days here I'd be tempted but I'd rather fish when not working), it is probably safe to say that it is not consequential. The ironic apart is that the shallower the water, the great a percentage of the time is determined by the electrical signal path, so your shallow readings will be more 'off' than your deeper ones. But again it is a matter of degree and ,without knowing empirically, I'd make an educated guess that it isn't much. However, for the record, I am not shortening mine because I think the accuracy I'd give up is greater than the error induced (if any) by noise from a coiled cable or the inconvenience of coiling the cables ( they stow nicely out of the way on the Marauder). But that's my opnion and preference.

From my understanding, the magnetic field produced by a wire coil is a function of the current.  Higher current produces a larger magnetic field.  Depending on how the measurement is made, it is possible that the current in the wire is quite small so that the field it generates is not significant.

With regard to splicing the wire, Surfingmarmot's analysis rings true.  Many of our sensors work on the same priciple and changes in wire length while potentially significant are usually quite small in comparison to the actual measurement being made.  I will only add that waterproof splices are tricky if not difficult especially if exposed to pressure/submergence.  In this case, you will probably be fine using heat shrink over the internal insulation and then heatshrink with glue or epoxy inside on the outer jacket to provide a water proof seal.  You may also want to rough up the outer jacket of the cable to improve adhesion.  In the absence of heatshrink wiht glue already inside, Liquid Electrical Tape would also work but I would be sure to cover it with regular heatshrink for extra strength.

Yes, I am gonna heatshrink it and use some sort of sealant too.

It is a gamble, but one I am willing to take.

For some dumb diddle reason I tossed (at least I can't find it) the old transducer for the unit that got stolen (same unit).

Anyway, I'm going to go for it this weekend.  I will let people know how it turns out.

MolBasser