transducer cable length

[fiestaMojo]

I searched the forum before posting this, I don't think my question has been answered in any threads - I've read that performance of a depth instrument can be affected by shortening the transducer cable, but what about increasing the length (given a good splice)?

 

[Roy10289]

To my understanding any change in the length of the cable effects the calibration of the instrument and its overall performance.

 

[Bill Roosa]

Cable length and depth transducers

The longer the cable the more capacitance (storage of charge) is shows. This results in less "signal" to the receiver unit if it is an analog type connection. Making the cable longer makes the voltage levels slightly lower is all that really means. If the transducer is sending digital information then that is not going to affect it one bit till you can make the cable long enough to drop the voltage a few volts (1000s of ft of cable).
You will lose more volts in your splice than you ever will on making the cable longer for the boats we are talking about so a good splice is important. Remember to "splice" the ground shield also as a break in the shield can introduce noise to the signal. Splicing a ground shield just means the entire wire bundle is surrounded by a conducting (aluminum foil) substance. And that substance is electrically connected to the wire loom ground shield. The easiest way to do that is to put the whole splice inside a metal terminal junction box and attach the wire loom shield to the inside of the box to both wires. Check by testing for continuity between the shield pins at each end of the cable. No continuity means no shield.
If you use a terminal block in the box is also makes a handy place to re-splice if you need to replace the transducer or remove it for maintenance.

 

[higgs]

Contact the manufacturer.

 

[Bob Poff]

Changing the length would also make the propagation time through the cable different.
Which would upset the timing of the return echos. Thus wrong depths being indicated.

 

[Johnb]

Changing the length would also make the propagation time through the cable different.
Which would upset the timing of the return echos. Thus wrong depths being indicated.

Perhaps not - the sound waves travel through water at about 5000 feet per second and the electrical siganls at maybe 2/3 the speed of light or 650 million feet per second, so to get an error of 1 foot you would need about 124 miles of wire (taking into account going and returning).

 

[Ron20324]

Ditto to replies #2 and #4. Contact the maker.

 

[Don12364]

Echo sounders RESONATE their PZT transducers at their natural frequency. (47KHz or 200KHz or what have you).
The capacity of the cable is a part of the resonant circuit so making it longer or shorter will tend to knock this tuned circuit off resonance. The result will be less transmitted power and less of the returned sonar energy being converted into signal pulses at the receiver i.e. double jeopardy. It should not affect the depth measuring ACCURACY.

Having said all this the tuning is fairly 'flat' and so small lengthenings or shortenings will not make too much difference to the SENSITIVITY. Probably changes of 5% of cable length would be tolerated by the unit.
Anyway you can always try and see. If it still works both at maximum depth and minimum depth you will have got away with it. If it does not work then you will need to reconnect the plug at the original point.
Because the frequency is low by radio standards you should not experience any significant losses at the joint. Just make sure it is waterproof. I would use self amalgamating tape fully stretched to cover the joint.
Most transducers come with plenty of cable for a typical boat anyway and it is often necessary to coil up the spare rather than cutting it off.
Are you installing it in an aircraft carrier?

BTW: My H376 has a conduit running the whole way from the depth and log transducers beneath the mast to just below the cockpit. It is a PVC tube which runs on the starboard side, under the cabin sole, bypasses the engine bay, under the aft cabin and passes through the rear bulkhead. From here the cable runs upwards into the steering console via the stern locker.
This pipe is well hidden but by feeling around you might find a 1½" PVC tube too.
Your present transducer cable should be in it already.

 

[LloydB]

If the cable were shortened and the performance changed, would you expect no change in performance were the length restored? What about adding the restoration length to the original? I think the question has been answered but just not stated as asked.

 

[garyc]

If you need a longer cable just buy an extension cable. No need to splice.

 

[SamLust]

Most of the manufacturers have extension cables available. I've used them on my Horizon and Navman sets, and I think, on my Raymarine stuff. Did not make a whits worth of difference. All of the units can and should be calibrated. If you insist on splicing you'll want to be real careful because the wires are very fine. I've done it, but only when there was no alternative, like buying it premade from the maker.