Old NASA Target - Spurious echos on shallow water

[AndersGu]

Just checking in case anyone has seen the same. What I see is pretty logical, but somewhat annoying..

It is an old NASA Target sounder. The transducer is on the inside of the hull. I tried a "cup" with castor oil, but it never worked so I just glued it to the inside of the hull and it works OK, apart from when you are in really shallow water.

Then it alternates between the correct 1.1 and 2.2. I assume that it picks up stray echos that echoed off the hull, back to bottom and up to reciver.

 

[Dipper]

My NASA Clipper mounted in the oil filled tube does the same. It did improve after I reduced the sensitivity but still sometimes gives double the depth in very shallow water.

Try reducing the sensitivity to see if that helps. I assume you can do that on the Target range.

 

[Guest]

You can tell when it's "bounce" echos - as they are multiples of the real depth ... reducing gain normally removes them - but care as it often at shallow depths means only a very slight twitch of the gain knob.
Digital displays are supposed to filter this out and generally are successful. LED dial displays are up to operator.

 

[AndersGu]

Problem is.... There is no gain knob on the Target... At least not that I can see /forums/images/graemlins/frown.gif

 

[Lakesailor]

You can set the sensitivity on the Target.
pdf : http://www.nasamarine.com/Instruments/images/Targetlogdpt.PDF

 

[AndersGu]

Great. Thanks! That manual appears to be different from the one I got when I bought the unit, but I must test ASAP! And set the keel offset too!