Tricks of the trade

Lon's saltwater grounding method

Depending on the combination of hydrophone, power source, and local electrical systems and electromagnetic fields, it is not uncommon to get a 60Hz hum in your audio data (low frequency system noise, aka ground loop noise). Here's a technique adapted from a method that Lon Brocklehurst uses for providing a "saltwater" ground to your electrical equipment.

Step 1: Prepare the grounding rod and wire

Braze a 1m length of 1/2" diameter copper pipe to an insulated wire long enough to reach from near or below the low-tide level (where the sand/gravel/substrate is always wet). At the shoreside end, strip the insulation back a bit (and optionally solder on a short lead with an alligator clip).

Here's what the pipe looks like after a year or so in the marine environment (corroded; beaten up by driftwood in storm waves). This one was strapped to the Bush Point wharf over the winter when much damage was done...

Repurposing the Bush Point ground for Sunset Bay involved first cleaning up the brazed area, pipe and wire:

Then I (Scott) used a heat gun to add some heat-shrink tubing over the braze (hoping that the hot inner glue would help seal the pipe-wire connection and maybe help the brazed area resist corrosion longer:

Step 2: Deploy the grounding rod in the ocean

Dig, hammer, or otherwise fix the copper pipe vertically in the nearshore substrate so that it is at least in wet rocks/sand, but ideally so that the deepest point on the pipe extends below the lowest low water level in your site's annual tidal cycle. Then secure the pipe to any available structure that allows you to run the wire back to your audio equipment. We often run it up a piling of a wharf, or just along with the hydrophone cable (e.g. through any intertidal protection).

This is a lousy photo, but you can see the copper pipe strapped with two black cam cleat cargo straps to the big cement pilings under the Sunset Bay wharf:

Joel is running the wire through the joists on the bottom of the wharf and up to the hydrophone streaming computer.

Step 3: Attach the new ground to your hydrophone computer system

Here's how Dave Bain provided a saltwater ground the the Raspberry Pi + Pisound system at Sunset Bay without needing to solder:

Note the yellow jumper cable connecting the white saltwater ground with the shield of the bare 1/4 plug inserted into the Pisound headphone jack.