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Re: [PSUBS-MAILIST] Sonar/Telephones was Propulsion
There is a company called Hamtronics that makes a line of ham radio
equipment. There are several modems they have to be used to modulate and
demodulate signals at 2400 and 9600 baud. At these baud rates they shift
tones between two values. I have used the 2400 baud units in kit form for
two applications and they work well. Neither of these modems require
handshaking. You just send and receive RS-232C levels between them. But
you will still have to modulate the transducer's signal with the tones
produced by the modem. Also, if you measured the signal produced by one
transducer using another and each was stationary in the tank, you may have
found a frequency where you got constructive interference in the tank which
may not necessarily be the best frequency for transmission. in open
water. I think if you develop a link that will allow human speech, you
will have no problem modulating and demodulating for data.
It is amazing how well a small transducer sends and receives high
frequency sound under water.
GB
At 08:26 PM 7/29/00 , you wrote:
>Gary, thanks for the info. there was some useful information there.
>Understand that what I was trying to accomplish was to transmit data
>through water using modems. I was just using the ultrasonic waves as a
>signal carrier through the water medium. I used a ~200KHz frequency
>generator, and 2 old military surplus transducers that I bought about 20
>years ago for experimentation. I finally got around to using them. Luckily
>I have a variable output generator and was able to determine the optimum
>frequency in the fish tank. Here's the concept that I used though: Since
>the modems are set up for analog signals (I did not want to use digitals
>for various reasons), I had to vary the signal from a high (1) to a low
>(0) state. To do this,I had to use a pulser to develop a set time rate
>that could easily be interpreted by the software that I designed at either
>high (1) or low (0) for the modem "sending data", (SD) and "receiving
>data" (RD). The receiving computer software essentially read the data in
>the buffer every 50 milli seconds. If the buffer had a value, it was
>considered a 1. If during that time it had no input, it was considered a
>zero. I could have used ASCII characters, but I really wanted to try this
>first. The biggest problem I had was initial handshaking between the
>modems. This turned into a real mess. I eventually realized that since I
>didn't have to dial up over a telephone line, that I could treat the water
>like a leased line and establish the handshaking up front by the software
>and eliminate all other error correction protocols and file transfer
>protocols since I did not need them.
>Any way as a result of my experiment, I think that I can make some
>significant improvements in data transmission. Again, thanks for your input.
>Suds
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