"Vito" wrote in message
...

"Rick" wrote in message
...
The cable should not be shortened at least that is what I was told. It
does not harm the unit to turn it on with out the transducer being
connected.

The transmitter sends a pulse of electromagnetic energy down the coax to
the
transducer at the speed of light. The transducer converts that to sound
which travels at (yup) the speed of sound in water; then it listens for
echos and converts them back to electromagnetic signals sent via the same
cable to the receiver. The receiver measures the total time required by
all
this to determine depth. If you cut 10' off the cable that determination
will be off by 2x the time required for a speed of light signal to do that
10'. Since the speed of light (186,000 miles PS IIRC) vs sound (about
1100
feet PS) that error is small.

It's not the cable delay that counts in this case. The cable capacity is
important here and is used as part of the tuned circuit that drives the
transducer. If you change the cable length, you change the capacity of the
cable and therefore the resonance frequency of the tuned circuit. The result
is that the sounder cannot generate a sufficient high voltage to drive the
transducer.

Meindert