Sensor Cables

[tim3057]

My B&G Focus echo sounder & log instruction book says don't shorten the spare length of the tranducer cables, just coil them up out the way somewhere. Not much spare room on a 24' boat to permanently store about 50' of pointless cable!

Why can't I cut it short?

 

[bruce]

expect most will say cut it, the maker says not to, because most will not do the job right with a bad splice etc. it is nothing more than 'coax' like for the vhf, and the transponder is the antenna.

 

[Landale]

Hi,

Without going into the physics etc.

Very often the lead and the transducer form a tuned circuit - if the cable is shortened this will change the tuning and so efficiency and sensitivity of the system.

Secondly, if the re-connection is in anyway flakey there will be a reflected return from it giving potentially false indication of depth.

Sorry, but best advice is coil it up unless you are confident of re-tuning the system and make a good connection or finding someone who is competent to do it.

For a further explanation see and don't say I didn't warn you!

cheers

 

[Oldhand]

My first reaction is depth is measured by timing the delay from a transmitted pulse to the received reflected pulse. However as the speed of transmission in the cable is so much faster than the speed of sound in water, I can't see cable length having any significant influence in the timing and subsequent depth calculation. However, as Landale has already suggested, the transducer system includes the cable and the transucer impedence/reluctance may be affected by shortening th cable such that it is no longer properly matched to the design of transmitter/receiver.

Argueing its just coax like for the VHF is irrelevant because VHF's have to be designed to operate with all makes of VHF antennas with a suitable VSWR 1.5:1 or 2.0:1 or whatever. These particular instruments are only designed to operate with the manufacturer's own design transducers and only the designer knows if the cable length is critical to the performance.

 

[Anonymous]

It's the capacitance.

 

[William_H]

So if you really wan to shorten the cable then cut and reterminate. If you find the performance not as good as before in terms of performance at depth then you could try measuring the capacitance of the cable removed and substitute this amont of capacitance across the cable at the join. However you could possibly stuff the whole system in which case reinsert the cable into the system and you may recover the performance. good luck will

 

[bruce]

i did not want to argue that coax was like...just that the wire is a connector between an antenna and a transmitter in simplest terms. being a member of the lower class, not being able to afford the real nice stuff, i have played with recycled heads and transducers, and have had good luck getting mismatched sets to work good enough use.

 

[tim3057]

I other words I should do what it says on the tin! Thanks to all for the advice, I will coil it up out the way somewhere.