Effects of mismatched depth transducer-head

[whipper_snapper]

What happens if you connect a depth sounder to an incompatible transducer ? Do you get no reading, wrong reading, reduced range or some other symptom?

The reason for asking is that we have a NASA Target depth gauge that gives very accurate readings in very shallow water, but looses the bottom at depths over 10m. This makes it pretty much useless for the sort of sailing we do.

The PO said the reason was that the transducer was for a different device (an old whirling LED thing) and provided the 'proper' transducer in a carrier bag. However, we have since discovered multiple reasons to doubt the sanity of the PO.

Before we mess around cutting holes in the boat, can anyone confirm that accurate readings but very poor range is likely to result from such a mismatch ? My understanding is that there are only two possible frequencies and I would not expect it to work at all with a sender at the wrong frequency, and would be even more surprised if it was accurate.

A complication is that the very steep V profile makes it hard to try it out fitted internally and firing through the hull.

Thanks

 

[steve28]

the transducer from both will be 150khz so will run the target and the older type. The most common reason for losing the depth is the traget does not have an adjustable gain so you have to set it either for acurate shallow water or acurate deep water. the setting in between is sometimesw hard to find.The type of bottom also affects it.

manual is on www.nasamarine.com
steve

 

[rob2]

Exactly as Steve said. NASA use the originally universal 150Khz type. You can check on the Airmar website for compatibility - they make most of the transducers anyway. Another possibility as a limiting factor will be the way the transducer is mounted and how much attenuation that is causing. If it's looking through the hull (in hull mounting), then you will be losing some power across the two interfaces compared with what is possible with a through hull mounting which has only one interface.

 

[cpedw]

I would expect something like that if the frequencies are not matched. The basic measurement is of time from pulse going out to pulse detected coming back. That time doesn't depend on the frequency used. But the size of pulse sent out and the sensitivity to the pulse coming back are both dependent on the frequency in use.
If the wiring is long enough, you can try dangling the new transducer over the side so the business end is in the water. Keep the bit where the cable emerges dry. Then you should be able to confirm if the transducer is compatible.
It may work less well from inside the hull becasue the hull reduces the signal somewhat as it goes out and as it returns, but careful siting should allow similar performance to be achieved.
To find a good location inside the hull for the trasnducer, put it in a plastic bag of water (again, keeping the cable entry dry) then put the bag up against the hull where you hope to fit the transducer. It should show whether it will work there.
Derek

 

[Billjratt]

The frequency may be the same on both units, but is the impedance? Also, has the cable been altered? Any variation will alter the efficiency of the transmitter - weak pulse, and receiver - mismatched, which will give the problems you describe. The Xducer ASSEMBLY must be right for the head unit to get maximum efficiency.