"Bruce in Alaska" wrote in message news:bruceg-
I hate to rain on your parade here Meindert, but most, if not all,
consumer Marine Depth Sounders, have Transformer Coupled outputs that
are resonate in and of themselves, and really don't care what is
connected to their output link as long as it isn't shorted.

That is technically impossible. And you as a radio man should know this.
Just like it is impossible to create a fixed antenna tuner that matches
anything between a screwdriver and a full size dipole, without changing a
tuning element.

Please read http://www.airmar.com/pdfs/technical/sensor.pdf. Specifically,
at page 21, right column, last bullet, it says that if the cable must be
extended, it requires removal of capacitance in the tuning circuit. So if
you short a cable, adding capacity is required.
In the example at the next page, a calculated capacitance of 2428 pF s shown
for the crystal. To get the example resonating, the calculations show that
6776 pF is to be added for proper operation.
Now, if you would cut a 10 meter cable in half, you remove 500pF from the
equasion, which will have significant influence on the proper operation.

Meindert