Mitsubishi Electric MUX-25TV - E1 User Manual download pdf (Page 59)

Fig. 2. A

surplus

hydrophone.

inductive

feedback that can cause the am-

plifier to oscillate

high gain levels. To

further reduce

the possibility of oscilla-

tion,

connect

0.1-

microfarad

capacitor

across the power supply pins of the two

integrated

circuits.

Underwater Hydrophone

the many

experiments I've performed

with

audio amplifiers,

listening

to under-

water

sounds has

been among

the most

interesting. When I was

high

school stu-

dent, some of my friends

and

used a

transistorized

amplifier salvaged from

cheap battery- powered PA

system to es-

tablish

voice

link between the deck and

the

bottom of a local swimming pool.

One of us

would

swim

down

the

bot-

tom

with the microphone

while

the others

remained on top to

listen. As

you

might

expect, the words were bubbly sounding,

but

it was

actually

possible to understand

most

what was

being said.

Later,

I used this same system

to listen

to the sounds produced by a captive por-

poise. For both experiments, the

micro-

phone was

low -cost

crystal

unit placed

inside a

mostly waterproof

plastic bag.

Recently, my interest

in underwater

sounds was revived as I was flipping

through

the pages of

Edmund

Scientific's

catalog and spotted a surplus

hydro

phone (catalog No. 41,759) for $9.95. I

promptly

ordered one.

its name

implies, a hydrophone is

microphone

specifically designed for un-

derwater use. The Edmund Scientific unit

completely encapsulated in black rub-

ber

and

plastic

and can be used

fresh or

salt

water

to a

300 -foot

depth. The

unit

has

a low impedance and

capacitance

approximately 15,000 pF. The hydro

phone's frequency response ranges

from

lOto6,000Hz

±4 dB(

±1

dB from lOto

2,000 Hz). Above 7,000 Hz,

the

hydro

phone's rolloff is

at a rate greater than 12

dB per octave.

Figure

a sketch of the hydrophone I

purchased from Edmund

Scientific.

Ac-

cording to the specification sheet, this hy-

drophone may have one or

two pairs of

leads. If present,

the additional pair of

Fig.

3. Connecting a

shielded

cable to the hydrophone.

L. STRIP LEADS

2. &END

S Row

psi

3. SOLDER LEADS

`. APPLY

HEAT-

SHRINKABLE

TUBING

.. HYD

RO PPoNE LEAD

.F_

SHIELDED

cABLE

SoLOER

Á-- =R

APPLY

510 coNE

SEALANT

leads facilitates connecting from two

four units in parallel. Indeed, you can buy

a string of parallel- connected

hydro

phones

from Edmund

for $39.95.

the

hydrophone

you

receive has an

extra pair of leads, it's

important to insu-

late the exposed end of

the

unused

pair to

prevent

any possibility

of inadvertently

shorting

the hydrophone's output.

small blob

silicone

sealant like that

used to assembled tropical

fish

aquar-

iums works well.

The specification sheet

supplied

with

the hydrophone

explains

how to

solder

shielded cable

to the hydrophone's

leads.

To avoid using the

tape suggested in the

spec sheet,

I used a slightly different

method. First, I exposed the two strands

bare

wire in the connection

lead

and

folded

one strand back

along the insulat-

lead. I then placed the exposed con-

ductors at

the

end

of a length of shielded

cable

alongside the two strands, as shown

in Fig.

After

soldering

the hydrophone's ex-

posed leads to the shielded cable,

I placed

a short

length

heat -shrinkable tubing

over the connection

and

shrank

snugly

over the soldered

wires with the heat from

a soldering

iron. Next, I

coated the entire

connection

with

silicone sealant. Finally,

soldered a shielded Y.

" phone

plug

to the

unused end of the shielded cable.

For best results, the hydrophone

should be securely mounted to

a suitable

handle, rod or pole.

Otherwise,

the

strain

placed

on the connection lead may cause

one or both of the

small

wires

separate.

Edmund

Scientific's specification sheet

recommends

using a

hose

clamp to attach

the

body of the

hydrophone

to the flat-

tened

end

length of

electrical conduit

(available from a hardware store). The

connection leads should then

tied

taped at intervals along the pole.

some preliminary

tests, I've used my

hydrophone

to listen to the

sounds in the

spring -fed

creek

that

flows about 1,000

feet from the old Texas

farmhouse

where

these words

are being entered into

word

processor.

This

stream

populated by

catfish,

bass, blue gill,

gar

and

various

kinds of turtles

and

frogs.

Though these

tests were conducted

during January

when

the

creek's

inhabitants

are much

less

in evidence, I

could

hear

a cacophony

Say

You

Saw It In Modern

Electronics

April

1986

MODERN ELECTRONICS

1 2 ... 54 55 56 57 58 59 60 61 62 63 64 ... 83 84

Comments to this Manuals

No comments

Mitsubishi Electric MUX-25TV - E1 User Manual Page 59

Comments to this Manuals

Related products and manuals for Split-system air conditioners Mitsubishi Electric MUX-25TV - E1