depth finder transducer frequency question

[RB]

Just found a couple of old transducers tucked away in a desk drawer in my
workshop. No clue as to what they're from, make, model, etc, nor as to
operating frequency.

If I recall correctly, the freq is the most important characteristic. Also
seems like the other thing is not to stick 'em on some depth finder that
overpowers them and pops the circuit that fixes the freq. Is all this
correct?

If so, what's some practical, reasonably simple way to determine their
design freq?

 

[Short Wave Sportfishing]

Just found a couple of old transducers tucked away in a desk drawer in my
workshop. No clue as to what they're from, make, model, etc, nor as to
operating frequency.

If I recall correctly, the freq is the most important characteristic. Also
seems like the other thing is not to stick 'em on some depth finder that
overpowers them and pops the circuit that fixes the freq. Is all this
correct?

Yes - it's a question of how much current the crystal can handle in
terms of RMS power from the signal transmitter - if they are older
transducers, it's a pretty safe bet they will handle 600 watts.

If so, what's some practical, reasonably simple way to determine their
design freq?

Jeeze - those can be anywhere from 25 to 200 Khz. depending on their
age and what they came off of.

Are there any identifying marks on them?

Later,

Tom
S. Woodstock, CT

 

[RB]

No marks whatever. That's why I am trying to figure out some simple,
practical way to figure out what the design freq is. Nothing comes to
mind, though.

 

[Gary Schafer]

No marks whatever. That's why I am trying to figure out some simple,
practical way to figure out what the design freq is. Nothing comes to
mind, though.

If you have a variable audio generator, hook it to the transducer.
Place an AC voltmeter across the transducer and slowly tune the audio
generator around the the most common frequencies that the transducer
could be. You should see a sudden rise in the voltage when you hit the
frequency.

Regards
Gary

 

[RB]

OK. Great idea. That should work. I think most of those old units worked
freqs from approx 50-200khz. Don't remember any outside that range for
small personal watercraft.

 

[Bruce in Alaska]

Just found a couple of old transducers tucked away in a desk drawer in my
workshop. No clue as to what they're from, make, model, etc, nor as to
operating frequency.

If I recall correctly, the freq is the most important characteristic. Also
seems like the other thing is not to stick 'em on some depth finder that
overpowers them and pops the circuit that fixes the freq. Is all this
correct?

If so, what's some practical, reasonably simple way to determine their
design freq?

Most of the Professionals would use a Signal Generator, Scope, and
Impedance Bridge, and then sweep the transducer to determine its
design frequency. Shoudn't be to hard if you got the test equipment.

Bruce in alaska

 

[Short Wave Sportfishing]

If you have a variable audio generator, hook it to the transducer.
Place an AC voltmeter across the transducer and slowly tune the audio
generator around the the most common frequencies that the transducer
could be. You should see a sudden rise in the voltage when you hit the
frequency.

Interesting, but how would you hook the unit across the transducer
without taking it apart?

Later,

Tom
S. Woodstock, CT

 

[RB]

}}} Interesting, but how would you hook the unit across the transducer
without taking it apart? {{{

If I understand the question, you would simply put the audio generator and
ac voltmeter across the coax lead at some point (between the braid and the
center).

 

[Henry]

A lot of talk here of audio signal generators.

Although depth sounders are referred to as "sonar" they do not work at audio
frequencies.

Hi-Fi equipment can work up to 20K (salesmen and status-seekers will clain
more)
This is the upper level for people with good hearing. By the time we can
afford boats and gadgets out hearing has deteriorated to much below this.

Modern depth sounders work at 200K. This is radio frequency.

Some years ago the most popular channel on BBC radio was on 200k. It would
seem that, if you wish to test your fishfinder, you might be better off
using a thirty year old European broadcast receiver and hold the antenna to
the transducer.

Henry

 

[Gary Schafer]

A lot of talk here of audio signal generators.

Although depth sounders are referred to as "sonar" they do not work at audio
frequencies.

Hi-Fi equipment can work up to 20K (salesmen and status-seekers will clain
more)
This is the upper level for people with good hearing. By the time we can
afford boats and gadgets out hearing has deteriorated to much below this.

Modern depth sounders work at 200K. This is radio frequency.

Some years ago the most popular channel on BBC radio was on 200k. It would
seem that, if you wish to test your fishfinder, you might be better off
using a thirty year old European broadcast receiver and hold the antenna to
the transducer.

Henry

It depends on how you propagate it whether it is audio or RF.
If you are transmitting audio you are transmitting an acoustic wave.
If you are transmitting RF then you are transmitting an
electromagnetic wave.

You can have RF transmitted easily at 10 khz. You can also have audio
at 10 khz, as an example.

A depth sounder transmits audio. An acoustic wave.

Although you could use an RF signal generator to test a transducer, if
the signal generator went down that low. Most do not.

While most better audio generators go up to about .5 mhz. Probably
easier to find than an RF generator that covers that range.

Yes RB, you have it correct as how to hook it up to the coax.
50 to 200 khz range will probably be where you find them. There are a
few that go up to 400 khz.

If I remember right 50 was common, 80, 120 or 125, 180, 200.
50 and 200 were the most popular. I may be wrong on some of the other
frequencies. Maybe some more that I have forgotten too.

Regards
Gary

 

[Henry]

It depends on how you propagate it whether it is audio or RF.
If you are transmitting audio you are transmitting an acoustic wave.
If you are transmitting RF then you are transmitting an
electromagnetic wave.

Thank you, this makes sense.
I was trained in radio and perhaps was being too simplistic. Yes, I was not
differentiating between acoustic pressure waves and EM waves. I should study
the workings of the transducer. Can anyone help here?
Does a transducer have a diaphragm vibrating at 200K?

I must confess that my training started over 50 years ago (in the RAF). It
was much simpler then (fishfinder, what's that?), and I now feel rather left
behind.

Henry

 

[Peter Bennett]

Thank you, this makes sense.
I was trained in radio and perhaps was being too simplistic. Yes, I was not
differentiating between acoustic pressure waves and EM waves. I should study
the workings of the transducer. Can anyone help here?
Does a transducer have a diaphragm vibrating at 200K?

Yes - actually, a piezoelectric crystal that vibrates at the operating
frequency.






--
Peter Bennett, VE7CEI
peterbb (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

 

[David Flew]

My situation is a little different. I've got a boat built around 1960, it's
got a thru-hull transducer with no markings. Presumably it's a little more
modern than 1960's!
Assuming that I can estimate the resonant frequency ( I've got only a
frequency generator and a decent multimeter, ) how do I decide if it's worth
while getting a plug to adapt the transmitter to my Lowrance X48?

Or do I just wait a year until I pull the boat out of the water for annual
maintenance and fit a new thru-hull transponder?
Regards
David

 

[Short Wave Sportfishing]

}}} Interesting, but how would you hook the unit across the transducer
without taking it apart? {{{

If I understand the question, you would simply put the audio generator and
ac voltmeter across the coax lead at some point (between the braid and the
center).

Thanks - that's not what I meant, but I think I answered my own
question just by thinking about it.

Later,

Tom
S. Woodstock, CT

 

[Larry]

My situation is a little different. I've got a boat built around 1960, it's
got a thru-hull transducer with no markings. Presumably it's a little more
modern than 1960's!
Assuming that I can estimate the resonant frequency ( I've got only a
frequency generator and a decent multimeter, ) how do I decide if it's worth
while getting a plug to adapt the transmitter to my Lowrance X48?

Or do I just wait a year until I pull the boat out of the water for annual
maintenance and fit a new thru-hull transponder?
Regards
David

I'd suggest you wait until you pull the boat out of the water and replace
it. The problem is that you can't identify it. Others have suggested ways
to determine the resonant frequency, but that won't tell you how much peak
power it will handle. I don't know how you can do that without destroying
it.

 

[Bruce in Alaska]

I'd suggest you wait until you pull the boat out of the water and replace
it. The problem is that you can't identify it. Others have suggested ways
to determine the resonant frequency, but that won't tell you how much peak
power it will handle. I don't know how you can do that without destroying
it.

If one can determine the Resonate Frequency of the transducer, then it
would make sense to go ahead and hook up the sounder head. If it blows
the tranducer your not really out anything since it would have to be
replaced anyway, during the next haulout. If it works you save yourself
a haulout, and have a working sounder now.

Bruce in alaska

 

[Bruce in Alaska]

Modern depth sounders work at 200K. This is radio frequency.

Well, maybe, but not for sure. Common sounder Frequencies are:

50 Khz
88 Khz
100 Khz
200 Khz

Most of the consumer type sounders are 200Khz, that is true,
but there are a whole slew of different types and they use different
frequencies, depending on the typical use.

Bruce in alaska

 

[Figment]

The early Seafarer (Flashing neon) sounders in the UK ran at 150kHz.

 

[Bruce in Alaska]

Yes - actually, a piezoelectric crystal that vibrates at the operating
frequency.

True, actually 90% of the piezoelectric crystal tranducers are Barium
Titanate Crystals and most of these are made by one company. (I forget
the name now, but they OEM to all the Sounder producers) The 28Khz
Transducers are Magnetic Restriction types and not crystals, and the old
WWII SubSignal "Big Whoppers" were also Magnetic Restriction types as
well. It's really hard to get crystals to resonate below 50Khz with the
power levels used by typical sounders below that frequency.

Bruce in alaska

 

[RB]

Hey! Great discussions. Thanks for the thoughtful inputs.

}}} Others have suggested ways
to determine the resonant frequency, but that won't tell you how much peak
power it will handle. I don't know how you can do that without destroying
it. {{{

Guess and go by weight is the only clue I'd have on these unmarked ones.

}}} If one can determine the Resonate Frequency of the transducer, then it
would make sense to go ahead and hook up the
sounder head. If it blows
the tranducer your not really out anything since it would have to be
replaced anyway, during the next haulout. {{{

Right on. Nothing to lose, really. Maybe something gained.