RE: [PSUBS-MAILIST] sound transducers

["Andrew Goldstein" <ag@desertstar.com>]

All,

Yes, the input voice signal is usually translated in frequency (heterodyned).  This has several advantages:
1) Get away from a bunch of ambient and possibly ship noise
2) Allow for efficient transmission with smaller transducers
3) Concentrate signal energy in a smaller bandwidth (SSB)
4) Possible some acoustic signal attenuation benefits depending upon what freq mixed to
5) Can mix different transmitters to different freqs (multi channels) so multiple users can use the system and
not interfere.

You can also do more complex mixing to spread spectrum which has noise immunity benefits and offers a lower probability of 
detection in some cases.

How far any transmission will travel depends on the source level and acoustic environment (noise level, water properties,  etc).
Most back of the envelope calculations are pretty inaccurate since the estimation of water properties and noise levels is difficult.

OTS buddy phones are pretty inexpensive, But not as inexpensive or fun and interesting as home built.

Also, as a plug for the Conf. next year.  I think Nuytco has a voice comms system as well....

Best,
-a


-----Original message-----
From: Joseph Perkel joeperkel@hotmail.com
Date: Sat, 15 Nov 2008 11:28:30 -0700
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] sound transducers

> 
> Jay,
>  
> I thought maybe something like this. I had always wondered, how it was possible to have clear voice comm with Alvin several miles down. Knowing that different densities are just going to have to have an effect, I just never delved into the details of how this is done.
>  
> Still, I understand the interest in a short range homemade system. Are the off the shelf solutions expensive?
>  
> I can remember diving and sometimes getting your buddies attention by shouting (grunting really),... "hey look"! Then off course, it's sign language time!
>  
> Joe
> 
> 
> 
> From: bottomgun@mindspring.comTo: personal_submersibles@psubs.orgSubject: RE: [PSUBS-MAILIST] sound transducersDate: Fri, 14 Nov 2008 21:57:58 -0500
> 
> 
> 
> 
> 
> Joe,
> For efficient transmission, the signal is translated in frequency (still audible but unintelligible) to maximize range and single side-band is used to conserve energy.  Anything else will have difficulties of one form or another.  Opening a basic sonar acoustic text will document this, you can?t get around basic physics.
> R/Jay
>  
> 
> Jay K. Jeffries
> Andros Is., Bahamas
> A skimmer afloat is but a submarine, so poorly built it will not plunge?
>  
>  
>  
> 
> 
> From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Joseph PerkelSent: Friday, November 14, 2008 4:55 PMTo: personal_submersibles@psubs.orgSubject: RE: [PSUBS-MAILIST] sound transducers
>  
> David, Not having any field experiences and out of curiosity, this brings to mind a question regarding underwater voice transmission in general. I've seen voice comm between Alvin and Atlantis, Calypso and the saucers, habitats,...etc. Is this voice comm severely scrambled (distorted by the seawater), and then reprocessed by the receiving equipment? Or, put another way, if I swim between divers with voice comm equipment, could I hear the conversation like I do prop noises? Joe  
> 
> 
> 
> From: dbartsch2236@hotmail.comTo: personal_submersibles@psubs.orgSubject: [PSUBS-MAILIST] sound transducersDate: Fri, 14 Nov 2008 15:36:04 -0500   To all:     The transducer for solids from which can be made the broadband voice transmitters are available on e-bay under "underwater speaker" at this time. These are selling for $26.95 but shipping is being provided. This is not a bad price if you were concidering delving into this area of study.   With a singing machine that is battery operated, a voice transmitter can be made from the use of this. (It still needs to be imbedded in molding plastic to survive deep depths.) And you will still need a means of hearing the return responce.   It sure would be great to talk back and forth between two submerged submarines or to your support boat without having to surface first.                                                                                              David Bartsch
> 
> 
> 
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> 



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