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Go Back   SailNet Community > General Interest Forums > Gear & Maintenance
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  #1  
Old 01-19-2011
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New Depth Sounder / Old Transducer (How To)

So it's mid season, your boat is in the water, and your old depth sounder dies. What are you to do? There is often a good chance that your transducer is fine and it's only the display that has died. Despite the transducer being old there is a chance it may be the same frequency as the new depth sounder. If it's a 200Khz transducer it will likely work with Raymarine and some others that are 200Khz. I've done this a number of times. While certainly not ideal, or the "perfect" solution, mixing old and new, this can save you hundreds of dollars in a short haul expenses if you need the changing out of a drilled through the hull transducer. Either way, if you're in a pinch, it is worth a try.

The new transducer that came with the display can always be installed when you haul for paint, or for the winter, if you are in an area where the water gets hard for half the year.

To use an old transducer you will want to ascertain what the model number or brand is and then hopefully you can track down the frequency. Often times the old depth sounder manual will tell you the frequency in the specs. The transducer frequency must match that of the display head to make it work.

In order to do this you will likely need to cut the old connector off the end of the coax. Many older depth sounders used an RCA connector and some used a BNC type. The center conductor of the coax cable is hot or the signal send wire and the shield becomes ground or the signal return wire.

To confuse everyone the new Airmar transducers, Raymarine, Garmin, Furuno and many others use Airmar as their transducer supplier, are often three wires, hot, ground and a shield. When using an old coax transducer just make the center conductor hot and the shield the ground. On the Raymarine ST-60 for example you can just ignore the shield input and use ground/black and hot/blue and it will work fine if it is a 200Khz unit.

Most of the old transducers for depth were 200 or 210 Khz but there were also some other frequencies used as well. If if your old transducer is a 210 Khz it won't work at all or accurately with a newer 200 Khz display. For this post I used a 31 year old Radarsonics 200Khz transducer with a 2010 Rayamarine ST-60+. This transducer also worked with my 2006 ST-60 non + model before it got hit by lightning. Interestingly enough the ST-60 and every other piece of electronic gear was wiped out by that lightning strike. The only thing still working was my trusty 31 year old Radarsonics transducer!! I also have the Raymarine/Airmar P-79 unit that came with the ST-60 mounted as a "shoot through" for back up but currently disconnected at the instrument.

STEP #1 Strip the jacket back about 3" and be careful not to cut the shield wires of the coax cable.




STEP # 2 - Using a mechanics pick or other pointy object carefully un-braid the shield wires all the way back to the wire jacket.




STEP #3 - Once the coax shield strands have been un-braided, carefully straighten them and then twist the wires into a single conductor.




STEP #4 - Cut a piece of heat shrink about 3" long that is large enough in diameter to get two smaller pieces of heat shrink under, one for the pos/send and one for the neg/return wires. Once this is on you can slide it out of your way for now.




STEP #5 - Using a smaller diameter piece of black heat shrink slide it over the twisted shield wire leaving enough poking out the end for a crimp fitting.




STEP #7 - Using a heat gun shrink the tubing then simply crimp on your terminals.




STEP #8 - When the negative/return wire is done strip a little off the end of the main conductor to fit a terminal. Next wrap the main conductor with aluminum foil, this replaces the shield you just removed, and slide some red heat shrink over it. Now hit it with the heat gun and shrink it.




This is what the finished cable ends will look like. You don't have to use red for your signal/send wire and could ideally use whatever color matches your new instruments color codes. In this case, with a Rayamrine ST-60, that would be blue. For DC simplicity I chose to used the standard red/black for pos/send and neg/return. Alternatively, yellow can also be used as a DC negative color.




This photo shows how NOT to hook you your old transducer to an ST-60. The silver square on the ST-60 is simply for the third shield wire of the newer Airmar three wire transducers. The blue is hot and the black square is for the neg wire. The red wire in this photo is in the correct socket but the black/neg/return signal wire is not.
WRONG WAY!



These three wires are from the Airmar transducer that came with the Raymarine ST-60 Depth. The black is the transducer neg/signal return wire, blue hot/signal send and the silver wire is the wires shield which they attach to the display.
Factory Wires:




Here is how to correctly connect an old 200 Khz transducer to a new Raymarine ST-60 depth display. Your transducer will work very well wired this way and can buy you time until a haul out. Shield goes to the black socket and the center conductor goes to the blue socket.
RIGHT WAY:




This whole mating of the new display to the old transducer will take about 20 minutes to perform, and it works very well.
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Old 01-19-2011
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Just curious, but is that RF Base unit for the Smartcontroller autopilot remote?

Nice article btw...
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Old 01-19-2011
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A nice, neat install. Should last a very long time.
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Old 01-19-2011
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Very timely!. I have new ST60 toys and the old instruments all do not work. That is two depth and one speedo. Does this technique also work for the speed trasducer?
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Old 01-19-2011
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Quote:
Originally Posted by NICHOLSON58 View Post
Does this technique also work for the speed trasducer?
Usually no, unless same brand, and even then it often does not work.
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I have all B&G stuff with a central computer and programmable remote displays. Supposed to interface with the Simrad autohelm, GPS, etc. All sounds great. Its like that 'blonde' joke. "lights on but nobody home". I get system check and all LCDs are alive but no useful output from anything. There is even an old stand-alone depth with the hot orange segmented digits, the kind that never fails. All of these and the Furuno radar are just ornaments. Simrad autohelm works PTL! The alternator was our final 'clue' with 14 of 16 diodes fried. Must have been lighting before we bought the boat. The plus side is that the stuff is old and we can replace at will. Muskegon is a nice place for a 'blind' boat. It is a big deep sand basin; no rocks. A hand-held GPS plotter is enough to keep you from running aground.
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Old 01-19-2011
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Maine, first off, good post! ..although I'd second SD's question

Here's a question from someone planning to do the reverse: I have a Raymarine Fishfinder Triducer installed (a long old story) and don't have several thousand$ for the proper display. I'm hoping to hook it up to an old Navman 3100 Depth display pretty-much following the same procedure you outlined above.

The old Depth transducer was 200kHz - the new one is 50/200kHz. I assume this is still ok??

Just checking..
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Old 07-09-2011
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Maine,

That's some crimper. it looked so much more effective than the ones I have, I looked it up, found it likely certified for aviation use and can cost new over $1,000.

Followed your directions to connect a 20 year old airmar to an ST40 and it works about 90% of time. The other sounder, a very old datamarine indicates all the time - except flutters in wakes, as does st40.

At anchor right now and not getting indication. Will toggle off every imaginable source of rf interference, then dive the transducer to see if it needs a clean-up, then reroute the cable, remake the connection, put ferrites on both the seatalk-power cable and the airmar cable, then ask Raymarine if there is an undocumented sensitivity adjustment in the st40, then pray.

odd that the old seemingly simple datamarine unit has a sensitivity adjustment but the nice new ST40 doesn't.

damn that crimper. I know I won't sleep well until i have one just like it.

john
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Old 07-09-2011
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Tacktick

Great Information Maine! However my 25 year old Impulse depth finder has the transducer tuned to 160 KHz so I'm going to have to do the whole nine yards. I'm going to try and avoid running another transducer cable to the helm so though I would go with the wireless (tacktick). Also will not drill another hole into the boat or try to use the old hole and instead install the new transducer as a shoot thru the hull. The tacktick system will only be for depth only (using their entry level system which calls for 12V at the display which is already there) so I'm not really getting the full benefit of the wireless system since I don't use wind instruments. What are your thoughts about wireless and shoot thru the hull transducer?

I also saw that Raymarine has recently (end of June) had bought out Tacktick and wonder about intergration problems of the two companies.
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fixed

Next time I'll look more closely at the lead-in from the transducer. Mine had a blue and black wire and the shield too. So this time, I put a connector on the blue, one on the black. and one on the shield and Voila!

FWIW, I built a GadgetPoole NMEA/Seatalk Bridge, repeater which has a display so you can see a whole lot of data depending on what you have it hooked up to and transfer it to a pc via a serial connection or serial/usb with a converter - works either way.

I use PolarView - PolarCom to navigate and it's very nice to be able to watch the depth and wind from the notebook. An in fact, this was the whole purpose in getting the st40 - to get digital depth information.

john
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