Re: [PSUBS-MAILIST] Desert Star Sport

[Jon Wallace <jonw@psubs.org>]

Frank,

Not addressed to me, but I'll throw in my two cents.  Most commercial 
pingers are ultrasonic.  The hydrophone that David came up with uses a 
"sonic" piezo element centered at around 3khz so it would not be 
resonant to the higher frequency commercial pingers and would not detect 
them.

The Desert Star scuba pingers provide both direction and range and can 
be used exactly as you've described.  Unfortunately we have never been 
able to succeed at getting directionality out of the HBH (home-built 
hydrophone) using 3khz piezo elements, however my experience was that it 
was very easy to determine range based upon the loudness of the "ping".  
Therefore, by running a grid-pattern you could "home" in on the pinger 
by just listening to whether the sound was getting louder or softer.  
Not the most efficient way of finding an object by any means, however, 
and similar to what you would have to do with a down-looking sonar or 
fish finder.

Jon


ShellyDalg@aol.com wrote:
> In a message dated 3/14/2010 8:06:39 P.M. Pacific Daylight Time, 
> alanjames@xtra.co.nz writes:
>
>     I have only had experience with cheap fish finders & have
>     questions about their reliability,
>
> Hi David and Alan. Gulping air......well, OK.
> Now back to the question of finding a sub......
> If a sub has a pinger attached, could a surface boat find it with the 
> hydrophone you ( David ) made ?
> Depending on directionality of the array, a direction for the sub's 
> location should be possible. Maybe then the pilot could motor over in 
> that direction and as the pinger got louder you may be able to tell 
> how close you're getting. At least staying within a pre-set minimum 
> distance. By rotating the pick-up you would know if the surface boat 
> needs to go left or right. Now, if you passed OVER the sub and the 
> pinger signal was now coming from behind the pick-up the pilot would 
> then stop or get out of the way in case the sub was ascending to the 
> surface. Be a bummer to ram your own surface crew.
> Maybe you could have two pingers with one stronger ( louder ) or more 
> frequent so by listening you'd be able to tell how close you were. 
> What makes a pinger anyway ? Is it just a thing that sends out a sound 
> wave at a set interval ? It seems the pick-up part is the hard piece 
> to make. So the returning signal can be figured how far away it is ( 
> function of time ? ) and what direction it's coming from ( array 
> set-up in degrees ?)
> Frank D.
>  




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