Transducer replacement

[tolhurstorganic]

Need to replace damaged transducer Bon NASA Clipper duet. Manual says not to cut cable. But is it ok to cut and rejoin to existing cable close to transducer providing the same total length is maintained.? To replace cable all way back to cockpit is a bit of a mission.

 

[Plum]

Need to replace damaged transducer Bon NASA Clipper duet. Manual says not to cut cable. But is it ok to cut and rejoin to existing cable close to transducer providing the same total length is maintained.? To replace cable all way back to cockpit is a bit of a mission.

I cut and joined my NASA sounder to the old cable, although the ovrrall cable length was roughly the same, and is still working well after 3 years.

 

[bedouin]

I've cut and soldered depth sounder cable with no problems. You could also cut and join with a coax connector but that is probably overkill. Just take care to make good connections

 

[Refueler]

Need to replace damaged transducer Bon NASA Clipper duet. Manual says not to cut cable. But is it ok to cut and rejoin to existing cable close to transducer providing the same total length is maintained.? To replace cable all way back to cockpit is a bit of a mission.

The reason they say not to cut cable is a matter of 'Timing' .... the length of cable is part of the timed phase to calculate the depth. Small change in length is not a problem ... but imagine some people would want to cut out a large amount of cable ..

Cut and joining - maintaining correct length is not a problem ... just try to make insulation of centre wire and then screen good order ...

 

[bedouin]

The reason they say not to cut cable is a matter of 'Timing' .... the length of cable is part of the timed phase to calculate the depth. Small change in length is not a problem ... but imagine some people would want to cut out a large amount of cable ..

Sorry I am not buying the one!

Signals travel along the cable at close to the speed of light (300,000,000 m/s) but the depth is calculated using sound signals (1,500 m/s) the impact on the timing of removing a couple of metres of that is going to be measured in nanometres - and my depth sounder doesn't measure that accurately

There are other ways shortening the cable could impact the system, e.g. by reducing the impedance or capacitance of the load seen by the transmitter, but I can't see that being an issue with something as simple as an ultrasound pulse.

 

[Refueler]

Sorry I am not buying the one!

Signals travel along the cable at close to the speed of light (300,000,000 m/s) but the depth is calculated using sound signals (1,500 m/s) the impact on the timing of removing a couple of metres of that is going to be measured in nanometres - and my depth sounder doesn't measure that accurately

There are other ways shortening the cable could impact the system, e.g. by reducing the impedance or capacitance of the load seen by the transmitter, but I can't see that being an issue with something as simple as an ultrasound pulse.

I don't disagree with your reasoning ... I am only quoting what Marine Tech told me .. I too felt that SoL was enough to say nuts to it .. but ...

 

[bedouin]

Just seen that Airmar (who make all transducers) do a junction box to join transducer cables that contains what looks like choc box style connectors.

Airmar Junction Box and Terminal Block

And their instructions make it clear it is fine to cut the cable and rejoin with one of those

 

[Refueler]

Just seen that Airmar (who make all transducers) do a junction box to join transducer cables that contains what looks like choc box style connectors.

Airmar Junction Box and Terminal Block

And their instructions make it clear it is fine to cut the cable and rejoin with one of those

Fine ... who's arguing ...

But would be interesting to see if any comment in any instructions given with that junction box ..

Just a comment - do not forget that Co-Ax cable has a property that other normal cables do not have ... the form of the Co-Ax works with the screen surrounding an insulator with central wire ... a Radio Tech I sailed with years ago showed a method of joining Co-Ax that maintained as best as possible that relationship :

He stripped back outer .. laid back the screen .... stripped the inner insulator ... cleaned the centre wire. He then joined the centre wires - he chose to lay alongside each other and run solder along ... he then used a sliced length of the inner insulator to rebuild the inner insulator with tape till it matched the cables ... then spread the screen along - meshing the two into each other ... no need to solder or join - just made sure well meshed into each other. He then used Self amalgamating tape to cover and secure ...

It may sound involved - but according to him - it maintains the signal and shield integrity ...

This is what online says about Co-Ax cable and why its so designed :

"Coaxial cables conduct alternating current instead of direct current, which means that the direction of the current is reversed several times per second.

If a general wire is used to transmit high-frequency current, this wire will be equivalent to an antenna that emits radio outwards. This effect loses the power of the signal and reduces the strength of the received signal.

The coaxial cable is designed to solve this problem. The radio emitted by the center wire is isolated by the mesh conductive layer, which can be grounded to control the emitted radio."

mmmm TBH - I have used that Techs method for various VHF's and radios / TV stuff and I can only say - I have not noted any failures ... SWR and various tests have passed as if there's no joint.

I only post this as a comment ... take or leave as you see fit.

Choc box joiners for Co-Ax ? For me - only on non critical low power joints ... never on anything that carries any real power !!

 

[Alex_Blackwood]

Sorry I am not buying the one!

Signals travel along the cable at close to the speed of light (300,000,000 m/s) but the depth is calculated using sound signals (1,500 m/s) the impact on the timing of removing a couple of metres of that is going to be measured in nanometres - and my depth sounder doesn't measure that accurately

There are other ways shortening the cable could impact the system, e.g. by reducing the impedance or capacitance of the load seen by the transmitter, but I can't see that being an issue with something as simple as an ultrasound pulse.

Refueler is correct. Length is important

 

[bedouin]

Fine ... who's arguing ...

But would be interesting to see if any comment in any instructions given with that junction box ..

Just a comment - do not forget that Co-Ax cable has a property that other normal cables do not have ... the form of the Co-Ax works with the screen surrounding an insulator with central wire ... a Radio Tech I sailed with years ago showed a method of joining Co-Ax that maintained as best as possible that relationship :

He stripped back outer .. laid back the screen .... stripped the inner insulator ... cleaned the centre wire. He then joined the centre wires - he chose to lay alongside each other and run solder along ... he then used a sliced length of the inner insulator to rebuild the inner insulator with tape till it matched the cables ... then spread the screen along - meshing the two into each other ... no need to solder or join - just made sure well meshed into each other. He then used Self amalgamating tape to cover and secure ...

It may sound involved - but according to him - it maintains the signal and shield integrity ...

This is what online says about Co-Ax cable and why its so designed :

"Coaxial cables conduct alternating current instead of direct current, which means that the direction of the current is reversed several times per second.

If a general wire is used to transmit high-frequency current, this wire will be equivalent to an antenna that emits radio outwards. This effect loses the power of the signal and reduces the strength of the received signal.

The coaxial cable is designed to solve this problem. The radio emitted by the center wire is isolated by the mesh conductive layer, which can be grounded to control the emitted radio."

mmmm TBH - I have used that Techs method for various VHF's and radios / TV stuff and I can only say - I have not noted any failures ... SWR and various tests have passed as if there's no joint.

I only post this as a comment ... take or leave as you see fit.

Choc box joiners for Co-Ax ? For me - only on non critical low power joints ... never on anything that carries any real power !!

The use of the choc box came from the installation instructions from an Airmar transducer (and almost all depth transducers are airmar). Their instructions are to cut and join with one of those if necessary (rather than trying to remove the end connector).

You are quite right in general about Coax being rather special wire and care in joining and termination is very important in most applications. Don't mess around with VHF, radar cables etc.

However depth sounders work on very simple pulses of sound at <500kHz - that is close to audio levels so not much more than a loudspeaker - so not going to suffer much by not being coax. Also the functioning of a depth sounder is not really going to be impeded by interference with the signal

 

[Alex_Blackwood]

The use of the choc box came from the installation instructions from an Airmar transducer (and almost all depth transducers are airmar). Their instructions are to cut and join with one of those if necessary (rather than trying to remove the end connector).

You are quite right in general about Coax being rather special wire and care in joining and termination is very important in most applications. Don't mess around with VHF, radar cables etc.

However depth sounders work on very simple pulses of sound at <500kHz - that is close to audio levels so not much more than a loudspeaker - so not going to suffer much by not being coax. Also the functioning of a depth sounder is not really going to be impeded by interference with the signal

Yes it will. the signal is sent as a pulse from the main unit to the transducer and onward. The the return pulse from the transducer is received back at the unit. Time = distance (Depth) If a spurious signal(pulse) from interference is detected you will get a false reading.

 

[Refueler]

Yes it will. the signal is sent as a pulse from the main unit to the transducer an onward. The the return pulse from the transducer is received back at the unit. Time = distance (Depth) If a spurious signal(pulse) from interference is detected you will get a false reading.

I was just posting based on instructions given with sounders I've handled. Whether shortening cable does create error - I am not about to test ! I'll just stick with the instructions.

But will say that - the wording is usually to not SHORTEN cable .. not about cutting.

Here's Nasa for example :

"
Select a position below the water level where the transducer
will point substantially vertically downwards towards the seabed ,
and where the transducer and its cable (do NOT shorten the
transducer cable) will be well clear of equipment which might be
a source of interference."

Note the capitalised NOT ... seems they really want you to know !!

 

[PaulRainbow]

Older style transducers and current NASA ones used coax, which was not supposed to be cut.

Most modern ones (excluding NASA) no longer use coax, these can generally be cut with no problems at all.

 

[PaulRainbow]

Yes it will. the signal is sent as a pulse from the main unit to the transducer an onward. The the return pulse from the transducer is received back at the unit. Time = distance (Depth) If a spurious signal(pulse) from interference is detected you will get a false reading.

This is not the case with most modern transducers. The pulse is generated within the transducer and data sent back to the display, or often transmitted to the N2K network. It's perfectly OK to shorten the cables to that type of transducer.

 

[Alex_Blackwood]

I was just posting based on instructions given with sounders I've handled. Whether shortening cable does create error - I am not about to test ! I'll just stick with the instructions.

But will say that - the wording is usually to not SHORTEN cable .. not about cutting.

Here's Nasa for example :

"
Select a position below the water level where the transducer
will point substantially vertically downwards towards the seabed ,
and where the transducer and its cable (do NOT shorten the
transducer cable) will be well clear of equipment which might be
a source of interference."

Note the capitalised NOT ... seems they really want you to know !!

Agree. See also #9

 

[Refueler]

mmmmm C'mon guys ... OP has a Clipper Duet and thats co-ax ... and is actually why I pasted words from the Clipper Manual ...

 

[Refueler]

This is not the case with most modern transducers. The pulse is generated within the transducer and data sent back to the display, or often transmitted to the N2K network. It's perfectly OK to shorten the cables to that type of transducer.

I know the Airmar sonar that feeds my Garmin 92sv .. that is not co-ax ... but I don't have the docs for it ... maybe one day I'll be bothered enough to download !

 

[Alex_Blackwood]

This is not the case with most modern transducers. The pulse is generated within the transducer and data sent back to the display, or often transmitted to the N2K network. It's perfectly OK to shorten the cables to that type of transducer.

I will bow to your knowledge on that one Paul. I still maintain that what I said about interference as I described is applicable.

 

[bedouin]

Yes it will. the signal is sent as a pulse from the main unit to the transducer and onward. The the return pulse from the transducer is received back at the unit. Time = distance (Depth) If a spurious signal(pulse) from interference is detected you will get a false reading.

Technically correct but not really an issue with modern electronics - might show up as a fish on the fishfinder though

 

[Scubadoo]

Interesting, I have just installed a new transducer and although I didn't need to make any changes to the transducer cable, I noted the instructions mentioned you can extended the cable with their ready made cables, how does this fit in with cable length and timing.