Of hydrophones and transducers

[whiteoaks7]

I want to listen to whatever comes in through the echo sounder transducer (not necessarily with the sounder attached). Does anyone have any technical info on these transducers (eg do they have an amp close coupled or are they passive? - What is their centre frequency etc?). Or, can anyone give me the name of a good technical contact at NASA marine who might be willing to help.

 

[hightech]

Does depend on the manufacturer (most are Airmar) but they are usually passive and their frequency is usually marked on the cable (most are 200khz).

Predominately they are piezo crystal, but some are coils.

Sorry to be a bit vague, but if you give some more detail then I can home it i n better for you.

 

[savageseadog]

You can't listen to the received signal directly the frequency is too high and the emitted and received pulses too short, the interval between the emitted frequency and the received pulse would be very short too. For the former issue the incoming signal would have to be multiplied or mixed with the outgoing signal frequency plus or minus 1000Hz or thereabouts. That way the signals would come into the audio range. The the other two issues would have to be dealt with by signal processing (probably digital). I take it that you are trying to re-create he ASDIC type signal that you get on those old war films with submarines.

It's involved but an interesting idea. It would give you an idea of when to drop those depth charges.

 

[fishermantwo]

As Savage sea dog has already mentioned, the incoming signal needs to be hetrodyned to a frequency such as 1000hz which is about the frequency of the timing pips on the radio. You can often hear low frequency, long range warship sonars through the hull of your boat, thats that high pitched squeal. Time to look around and see if you are about to get run over.

 

[whiteoaks7]

Sorry Guys, I obviously misled you a bit - I don't want to listen to the ultrasound pings or the echoes, just the ambient sea noises. I've used a home made hydrophone to do this (Maplin piezo sounder and a couple of amplifier stages) but (as always with my kit) the mechanics broke down and the housing leaked, so it occured to me that the built-in transducer might work better. I'll give it a try, however, if the piezo is optimised at those hight frequencies I guess it won;t work too well at audio.

Cheers