On 27 May 2006 16:41:36 -0700, "Queeg" wrote:

I am installing a Garmin 3010C chart plotter on a new boat. It uses a
Garmin GSD20 black box to show depth & fish. The GSD20's transducer
has a 50 kHz & 200 kHz signal.

I want to have a separate depth sounder that is independent of the
Garmin. I have been told that two transducers on the same frequency
will interfere with each other. I have searched in vain for a
depthsounder that uses other than 50 or 200 kHz. I did find an Airmar
Smart Sensor that uses 170 kHz or 235 kHz, but it sends its signal to a
plotter or radar screen. I want a simple gauge on the dash as a
backup.

1.Does anyone know of a depthsounder that uses other than 50 or 200
kHz?

2. Has anyone run two transducers on the same frequency with success?
Mine will be about 12 feet apart on the transoms of an aluminum
catamaran.

What you need to know is that expensive transducers run on the same
frequency but have lots of crystals in them so they send multiple
signals to the computer and screen. This allows for more detail and
also lets the unit work at high rates of speed. The transducers that
do this cost upwards of 800 dollars and are made for expensive units.

I haven't found details on how they do this, but my guess is that you
have to a computer chip style reciever that is programmed to translate
all the signals and deal with them.

There is work going on to make transducers and systems that not only
tell you where and how big fish are, but also what kind of fish it is.
The idea, is, the unit would be programed to sort this information out
by knowing things about fish that is specific to certain species and a
sonar can gather information on. Since sonar works on the density of
an object and fish bodies are the same density as water, that only
leaves air in the fish for the sonar to bounce off of. So really the
only data sonars work from are air bubbles and airbladders.