Log/sounder interference

[howardclark]

I decided to relocate my instruments this year. After various wiring hiccups (such as acheiving 96 knots when the fridge was turned on) it all now works except for the fact that when the Echo sounder is on it gives about 1 knot on the log display.
The sounder is an Apelco fishfinder. The previous owner had exposed the transducer wires from the display to add a short extension - about 1m. This dosen't seen to affect the sounder's accuracy.
The log is an old Stowe Navigator 2 with a traditional paddlewheel.
The transducer and paddlewheel wires are not in contact - I kept them well apart.
To my surprise, if I detached the Apelco transducer I still had the interference. So thinking the interference may come from the power supply wires, I put the Apelco on a completely different circuit. Still no joy!
I can't think what to do next - any suggestions?

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[Seal_surfer]

Howard,

The problem is very likely to be that I metre extension on the souder signal cable allowing noise to radiate out into the log system. The shielding screen of the cable may not have been properly reinstated at the joint and I believe the sounder pulse would be quite intense and likely to cause interference. Try depowering the sounder or can you substitute/reinstate a complete unmodified echo transducer and lead to prove this is the cause.

Good luck,

Phil.

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[longmoor]

Having recently experienced difficulties with the depth sounder on one of our boats, I know that the length of cable between the transducer and the amplifier (PCB) is critical. Having said that, if you can specify the length of cable the amplifier can be calibrated by the manufacturer/agent. Fish finder?

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