The threshold on mine is not very steady. It moves about irregularly. I set it to barely audible over wet sand and if the waves are loud, I set it just a hair higher. Took me several hours of hunting with it before I was hearing deeper targets. The deeper targets move the threshold in a smoother way as the coil passes over the target even if it is a very small change. The normal threshold doesn't have the same change pattern; kind of choppy but not real regular. Sometimes the normal threshold variation makes me go back and recheck a small area when I think I heard a smooth change; then I also slow down the sweep a lot to be sure of what I am or am not hearing. If it repeats on coil sweep, I dig.
I have also had some interference; from other detectors, from some nearby push to talk radios when they are first keyed and one time something that I thought was a shallow target sound, but was too short of a burst and not consistent with sweep; so I raised the coil in the air for a few seconds and got more "hits". Since these random hits got fainter and then went away as a large boat / ship moved out, I think it was related to the boat.
I did have a hunt when the detector sounded off when waves washed over the coil and when I set the coil down on the sand. Unscrewing to coil connector from the detector and then reconnecting it solved that one.
I have found that I don't get as many tabs and bottle tops if I stay in the always wet sand and water with the Sand Shark and hunt the transition and dry areas with a different detector. Still get some junk, mostly hair pins, but not nearly as many tabs and bottle caps.
tvr
