OK to shorten sounder transducer cable?

[ChrisO]

I've just bought a new Garmin Fishfinder 90 to replace a dead echo sounder. To install it requires threading the cable through a narrow metre long channel which the connector at the end of the cable won't fit through.

I want to cut the cable, shorten it and then splice it back together. I've heard that shortening the cable is bad as the unit is calibrated to a particular cable length and that cutting the cable is bad as sonar signal will reflect off the splice and kill the echo sounder. Is this true, or will I get away with it?

Many thanks,
Christopher

[Nasher]

All the advise I've heard is not to do it.

I worked at Raymarine for a while and asked the question.
The 'tuned to cable length' didn't come in to it, more the standard of join that would be made, and the possibility of adding some resistance.

Nasher

[codprawn]

I remember all the fuss about satellite cables needing to be of very high quality and to have proper joints etc. I had a dish that I used to prop up in the garden with the wire coming through the letterbox - all I did was twist the wires together and it worked fine!!!

[jwalker]

.

Originally Posted by codprawn

...- all I did was twist the wires together and it worked fine!!!

...don’t confuse being lucky with being right. ©Jono

[codprawn]

Nah used to do it all the time - because of the winds we get I wouldn't mount the dish on the house. Just propped it in the garden when we wanted to use it. Once the picture went off - turned out a slug had crawled onto the LNB - a bit of salt and the picture was fine!!!

[Limey Linda]

I need to do the same thing so that I can move the transducer from the transom to the bilge sump.That job is a little bit down on the list but I plan to splice the cable using dielectric grease filled wire nuts. I will then place the whole spliced assembly in a piece of tubing and seal the ends with silicoln.

[codprawn]

Nothing beats greased nuts.....................

[Pete7]

Chris, had to shorten Garmin cables twice now, one yesterday, both worked afterwards. The through hull type have two wires blue and black plus non insulated earth, the transom mounted type I think 5 for the speed sensor.

The cable has a foil insulation, replace if you can but it's not critical. Just go for it.

Pete

[Chris]

I spliced in a new transducer when my old one snapped off and I did not want to drag a new cable through the trunk.

I soldered each wire and used heatshrink on each join the covered the lot with a piece Adhesive heatshrink.

I'm confident it will stand the tests of time.

[jyasaki]

Originally Posted by Limey Linda

I need to do the same thing so that I can move the transducer from the transom to the bilge sump.That job is a little bit down on the list but I plan to splice the cable using dielectric grease filled wire nuts. I will then place the whole spliced assembly in a piece of tubing and seal the ends with silicoln.

Use Ancor adhesive lines shrink butt connectors. Two crimps and a heat gun and you're done. If you want to be really anal, add another layer of adhesive lined shrink tubing over that.

jky

[ChrisO]

Many thanks to everyone who replied.

The cable was cut, shortened to a metre in length and spliced successfully.

Inside the cable we found a braided uninsulated wire and two pairs of insulated wires; red and black (probably power), and green and white (probably data). Each pair was wrapped in foil shielding. After cutting the cable each wire was soldered and the join covered in electrical tape . We wanted to use heat shrink but it proved too fiddly. The shielding was too delicate to solder and there wasn't enough to cover the soldered and taped joins so we wrapped each pair of wires in kitchen foil. The whole thing was then covered in self-amalgamating tape.

The echosounder works fine and although we haven't rigorously measured its accuracy it seems accurate to at least within 10%.