Cut transducer cable - repair or new?

[slawosz]

Hi,
I have old transducer cable on my boat, which unfortunately was cut before I bought it. I wonder if I should repair it (where I can find new connector), or should I install new one - I am planning to buy Nasa deeper. I wonder how hard would be pulling out old transducer - boat has nearly 50 years, and I think it might be there from new?

 

[lw395]

Transducer are generally matched to the depth sounder, with the length of cable part of the equation.
I expect you will need to use the cable and transducer which comes with the new sounder head unit.
Ancient cable should not be relied on if it's been in the boat a long time.

 

[DownWest]

I just had the same problem, so I soldered the centre core after carefully cleaning it (acid then flux) as the water had corroded the copper. Heat shrink on that joint, then cut back the outer copper about 50mm each way and wrapped some fresh copper from spare co-ax and soldered that at each end. More heat shrink over that and cross fingers. This way the length was kept the same, less about 8mm, which is a small % of the total. Obviously you have to remember to put the heatshrink over the cable before making any joints......

 

[jiris]

Transducer are generally matched to the depth sounder, with the length of cable part of the equation.
I expect you will need to use the cable and transducer which comes with the new sounder head unit.
Ancient cable should not be relied on if it's been in the boat a long time.

Unlike on radar, the length of cable is not critical here. The reason is, depth sounder works with sound where the speed of the signal is negligible in comparison with the speed of the electric signal going through the cable. The age and condition of the cable is something what has to be given some consideration though.

 

[LadyInBed]

Most of the old transducers were either 200 kHz or 210 kHz but there were also some other frequencies used.
If your old transducer is a 210 kHz it won’t work at all or not accurately with a newer 200 kHz display.

 

[jwilson]

You can certainly shorten echo sounder transducer cables, so I can see no reason not to join cables either as long as both joints and cables are good. I might be wrong but I don't think there is anything magical about the exact length of cable supplied with a new transducer (or radar cables for that matter).

 

[jiris]

You can certainly shorten echo sounder transducer cables, so I can see no reason not to join cables either as long as both joints and cables are good. I might be wrong but I don't think there is anything magical about the exact length of cable supplied with a new transducer (or radar cables for that matter).

There is a fundamental difference between radar and depthsounder. Both measure the time between a pulse being transmitted and echo received. But, the pulse in the sounder case is sound, doing some 1,500 m/s. Then it get converted into electric pulse, doing some 3,000 km/s through the cable. The total time is virtually not affected by the length of the cable, unless we are talking kilometres ;-).
In radar, on the other hand, the speed of the signal (radio wave) thorough the air is the same, as the speed of the electric pulse in the cable. If you change the length of the cable, the timing will be out and at the best case you get the image distorted. Some radars allow adjustment, others have to work only with a fixed length of cable.

 

[lw395]

Unlike on radar, the length of cable is not critical here. The reason is, depth sounder works with sound where the speed of the signal is negligible in comparison with the speed of the electric signal going through the cable. The age and condition of the cable is something what has to be given some consideration though.

It is completely unlike a radar cable. It's not really working as a transmission line, it mostly looks like so many pF/m connected across the transducer. Fiddling with it can send it off tune, greatly reducing the sensitivity of the sounder.

 

[William_H]

It is completely unlike a radar cable. It's not really working as a transmission line, it mostly looks like so many pF/m connected across the transducer. Fiddling with it can send it off tune, greatly reducing the sensitivity of the sounder.

+1 it is the total capacitance of the cable that matters hence keep it the same length approximately. OP should IMHO repair and join the cable and try it with the new sounder. As said it is the water proof aspects of the join that matter over the long term. If the old transducer works it may have limited range performance but that may not matter. Certainly a lot easier than replacing the transducer. Which you can do if it proves necessary. ol'will

 

[lw395]

I would use the new transducer.
I would not be connecting a new sounder head to some relic I found in the bilge.

 

[simonfraser]

If you need to replace it, mark the centre of the old transducer on the outside of the hull
Use a hole cutter the same size as the diameter of the existing hole
Chop off the flange
Quite straightforward and possibly less hassle than repairing a very old cable etc.

 

[slawosz]

I bought Nasa Target 2, and installed it on one side. Works perfectly (checked with lead line). Thanks!