NASA TARGET 2 depth sounder

[charlesmarchcambs]

I need to adjust the sensitivity (swept gain) but the handbook is not clear if a big number is more or less sensitive. Can anyone help please?

 

[VicS]

I need to adjust the sensitivity (swept gain) but the handbook is not clear if a big number is more or less sensitive. Can anyone help please?

The number you set is the depth, in metres, beyond which the sensitivity increases. That's why they call it the sensitivity threshold.

The larger the number set the deeper that threshold will be.

 

[charlesmarchcambs]

Thanks VicS. that helps me a lot. If I understand you correctly with the factory setting at 0.0 the receiver sensitivity is relatively low as at shallow depths there might be false echoes around that we do not want to receive. I am installing it on a RIB between the two hull skins (wet often) using the In-Hull kit. I wondered if there is any point in fussing with vegetable oil in the tube as it will gradually be replaced over time with water, which I guess is just as good anyway. Am I wrong please?
Charles

 

[VicS]

Thanks VicS. that helps me a lot. If I understand you correctly with the factory setting at 0.0 the receiver sensitivity is relatively low as at shallow depths there might be false echoes around that we do not want to receive. I am installing it on a RIB between the two hull skins (wet often) using the In-Hull kit. I wondered if there is any point in fussing with vegetable oil in the tube as it will gradually be replaced over time with water, which I guess is just as good anyway. Am I wrong please?
Charles

No I think you will find that when set to 0.0 there will be no band of low sensitivity so that reflections from nearby surfaces etc will disrupt the true reading of the depth. You increase the setting to create and increase the width of this band of low sensitivity.

With a rib you have no keels and about the only thing that will upset the reading will be air bubbles entrained in the water passing under the hull. I'd start with it set to a low figure and increase it progressively until it gives consistently sensible readings for the depth.

You may have point about the oil in the tube but I think I would use oil and seal the top to prevent water entering ... you don't want it to freeze if you forget to tip the water out in the winter.
OTOH
I am thinking about resiting mine. If I do I wont bother with the tube of oil. I'll make a bracket to support the stem and stick the face of the transducer down to the hull with a good dollop adhesive sealant.

 

[charlesmarchcambs]

Thank you VicS.

So I understand:
a) With the 0.0 initial factory delivered setting, all depths have the same high sensitivity, and as you say at shallow depths any spurious reflections might cause errors in the reading.
b) If I set the sensitivity to for example 5.0m, only depths between 5.0m and 100.00m have high sensitivity.

Do you have a RIB situation? If so I guess a limitation on your 'good dollop adhesive sealant' is ensuring that the sealant flows well and does not introduce any air bubbles but that should not be too difficult. I do however wonder if sealant would provide enough strength in the water slushing chamber. Perhaps this is the point, the opoxyed tube is the strength and the oil is the good air gap free medium. I am now inclined to follow your idea of using oil in the tube and sealing the top against the water.

My main use is to protect the prop in shallow depths and in particular the slip. The prop is 0.4m below the transducer. The NASA Target 2 minimum measured depth is specified to be 0.8m.

c) If I set Keel Off-Set to 0.4m and the Shallow Alarm to 1.0m, so the alarm will go off when the sea-bed is 1.4m below the transducer and 1.0m below the prop. The problem with this is I have about 60 members who helm to be confused about the effect of the depth non-linearity after the alarm goes off.

d) I am now wondering about setting the Keel Off-Set to 0.8m and the Shallow Alarm to 0.5m. If I am understanding correctly this will effectively give me 'display-linearity' and the alarm will go off when the sea-bed is 1.25m below the transducer and 0.85m below the prop.

Is my logic in d) OK, seems to good to be true!

I hope I an not too boring.

Charles

 

[ghostlymoron]

I've found with NASA equipment it's best to ring the excellent after sales team rather than get various opinion on this forum well intentioned as it is. Their always helpful and the advice is spot on.

 

[PaulRainbow]

If sticking transducers down the best and generally recommended stuff to use is slow drying epoxy. Silicon/Sikaflex type sealants are not recommended.

 

[Bliss]

Is this chat still open. With a half meter under the keel the nasa target sounder is fluctuating from 2m to 25m. I know for sure there is only half metre because Iv checked with a drop line. Should I bring the threshold up or down. Please help

 

[VicS]

Is this chat still open. With a half meter under the keel the nasa target sounder is fluctuating from 2m to 25m. I know for sure there is only half metre because Iv checked with a drop line. Should I bring the threshold up or down. Please help

If the reading was fluctuating between a very low reading and a larger true reading I'd suggest you try increasing the threshold but that is not what is happening.
How does it behave in deep water?

Id check connections to the transducer and the oil in the transducer mounting, assuming its in a oil bath

 

[Bliss]

If the reading was fluctuating between a very low reading and a larger true reading I'd suggest you try increasing the threshold but that is not what is happening.
How does it behave in deep water?

Id check connections to the transducer and the oil in the transducer mounting, assuming its in a oil bath

Hi Vics. ...Thanks for replying. In deep water it behaves normal. It only fluctuates in shallow water under 1m. Iv tried playing with the threshold with no response. both oil bath and connections seem to be ok.