Hi Tokteacher! What sub is it exactly that you purchased? unless i'm missing something, it is not mentioned in your post.

I'm running a Robbe Seawolf v2, and had some similar problems: for no apparent reason the sub would drop dead in the water. I solved this by replacing all the AMP power connectors with DEAN connectors.
For the antenna: you may want to consider weaving it around a circular piece (wood or plastic) that follows tube-shape of the sub. (hope you get what i mean... it's hard to explain). I have a TT Neptune SB-1 in which the antenna is mounted this way and it has excellent reception.
Also check for interference: there may be interference that only exsists around the pond area that you don't have in your workshop.
I may be repeating things you already know but: Subs only benefit from frequencies up to 41Mhz, anything higher then that just doesn't penetrate the water well enough.

One more thing you may find interesting: for my Seawolf i added a digital spirit leveler that controls the aft diveplanes. I got this from Alexander Engel, it is called an LR 2.2It helps running the sub level and prevents it from making hard nosedives. It won't do you any good if the stuck diveplane condition is caused by interference though.

Hope i gave you some ideas!

Grtz,

Bart<br type="_moz" />