[PSUBS-MAILIST] OTS and motor controller noise

Tue Apr 29 12:59:15 EDT 2025

I happen to have my former sub Snoopy back in the shop because her current
owner has engaged me to recommission her. The job is about 99% done, and
the comms already installed, so I just conducted an experiment. I have the
same setup as Dave; SSB-2010 inside the cabin running on its own dry cell
batteries, connected to the transducer by a cable that is potted through a
penetrator without cutting. I had left that cable longer than needed, in
case the owner decided he wanted the OTS unit somewhere different.

I turned on the thrusters and started moving the OTS all around inside, and
also routing the cable along different paths. Here are the conclusions:

1) As one would expect, there is much less noise when the thrusters are at
either zero throttle or full throttle. All the noise is in between, when
the signal is choppy.
2) The noise is completely insensitive to the position of the cable. BTW
the cable I'm using was the OEM cable on another comms system similar to
OTS. It's a small diameter shielded single conductor, where the shield is
not grounded but used as a second conductor.
3) Almost all of the variation in noise comes from proximity of the OTS
unit to the speed controllers. There is also a bit of noise if its placed
close to the battery cables, but it's nothing compared to the noise
emanating from the controllers.

So... the conclusion, at least in my case, is to place the OTS unit as far
from the speed controllers and battery cables as possible. David, does that
match the location of your OTS unit?

Best,
Alec

On Tue, Apr 29, 2025 at 12:54 AM David Colombo via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> Jon, youve got me thinking on this one. In the VAST, i have the diver unit
> inside the sub, a continuous non cut cable potted to the thru hull
> penetrator. The diver unit has its own 6 AA battery pack. With the pair of
> 36v 101's, and wearing the headset, i have not had any issues with bleed
> over noise. I am planning on adding the topside unit inside as a new comms
> like you. My 101's are controlled by their own minnkota pwm which are on
> the 36v lipo4 battery pack.  The hotel loads are on their own 12v lipo4
> battery pack, which is where i plan on connecting the topside unit.  I will
> run a test to see if i can find any signal interferance using the hotel
> load battery vs its own 2-6v battery pack, and let you know what i find.
>
> On Mon, Apr 28, 2025, 4:24 PM Alec Smyth via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
>> I've had mine to 250', but it was inside the sub. That said, the effect
>> on the audio quality was remarkable. It was perfectly clear, but if you
>> ever talked to your friends through a long garden hose as a kid, that was
>> exactly how it sounded. Which was great, because it made it feel spooky and
>> deep!
>>
>> On Mon, Apr 28, 2025 at 4:35 PM Sean T. Stevenson via
>> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>
>>> I have had a SSB-2010 a bit deeper than 130 as a diver without flooding
>>> the housing, but I don't know how deep it will go without compensation.
>>> That limit is the standard recreational diving depth limit for
>>> no-mandatory-decompression-stop diving, and it is likely that it was both
>>> designed and rated accordingly.   These units have no helium speech
>>> descramblers, so they are of limited utility for ambient pressure divers as
>>> you go deeper. The donald duck voice on top of the limited bandwidth of
>>> ultrasonic comms at all makes intelligibility a challenge.
>>>
>>> I had the unit to ~165 fsw, and I suspect that you could push it deeper,
>>> but you would void any warranty.  I'm using PowerCom 3000D units now, and
>>> these have similar depth ratings.
>>>
>>> Sean
>>>
>>>
>>> -------- Original Message --------
>>> On 2025-04-28 10:59, Jon Wallace via Personal_Submersibles wrote:
>>>
>>> SB-2010 is rated to 130 feet by OTS.  Has anyone tested one to deeper
>>> depths?
>>>
>>>
>>>
>>> On Monday, April 28, 2025 at 01:15:01 PM EDT, hank pronk via
>>> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>>
>>>
>>> Jon, put the whole unit outside the hull.  I have zero issues with
>>> this.  I just put fresh batteries in for each dive
>>> Hank
>>> Sent from my iPhone
>>>
>>> On Apr 28, 2025, at 10:16 AM, Jon Wallace via Personal_Submersibles <
>>> personal_submersibles at psubs.org> wrote:
>>>
>>> 
>>> Not a lot of room to work with of course inside the cabin.  My
>>> controllers are mounted up near the top of the hull, the coax comes in from
>>> the bottom and is probably only about 18 inches laterally from the
>>> controllers.  The coax cable thru-hull is only 5/8 inch diameter (15.8 mm)
>>> so PL259's won't fit through it to allow me removal for maintenance which
>>> is why I opted for SMA.  I suppose I could try it since I won't be removing
>>> the cable regularly but it's definitely going to be a PIA change.
>>>
>>> No I'm not sure whether the noise is electrical or acoustic in source
>>> but now that you've asked I can tell you that the controllers make an
>>> audible tone when the PWM is active, even with the OTS off.  The tone
>>> changes of course depending upon the PWM frequency I select, but it is
>>> always there.  The same tone comes out the OTS, but amplified.
>>>
>>> Jon
>>>
>>>
>>>
>>> On Monday, April 28, 2025 at 11:51:58 AM EDT, Sean T. Stevenson via
>>> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>>
>>>
>>> Two things I would look at:
>>>
>>> 1) Relative location and shielding between the motor controller and the
>>> transducer cable.  Is additional shielding (conduit?) possible?
>>>
>>> 2) I have encountered problems in the past with noise on coax due to
>>> impedance mismatch / partial signal reflection at any connectors. In my
>>> experience, this is solved by moving from RG58 up to RG8, but you don't
>>> have that option because the transducer is a potted assembly. If you have
>>> enough cable tail available to experiment, I wonder about swapping the SMA
>>> connectors for PL259 to see if that makes a difference.
>>>
>>> Are you certain that the noise you are hearing is being introduced
>>> electrically, and not acoustically in the ultrasonic range of the
>>> transducer?
>>>
>>> Sean
>>>
>>>
>>> -------- Original Message --------
>>> On 2025-04-28 06:47, Jon Wallace via Personal_Submersibles wrote:
>>>
>>> Hey folks,
>>>
>>> My OTS STX-101 receiver is picking up some fairly significant and
>>> annoying electronic noise from my Roboteq PWM motor controllers.  I tried
>>> changing channels on the OTS hoping a different frequency might help but it
>>> didn't.  I also tried changing the controller PWM frequency between a range
>>> of 10khz and 24khz but nothing between those frequencies made a significant
>>> improvement.  The noise is enough to override the normal squelch setting
>>> but at the same time a strong communication signal through the OTS
>>> transducer is enough to override the noise.
>>>
>>> My configuration has the transducer outside the hull and receiver inside
>>> the hull which required cutting the cable.  I potted the cable in a
>>> thru-hull and reconnected the cable inside the cabin with RG-58 SMA
>>> connectors (soldered, not crimped).
>>>
>>> In talking with a couple other folks it seems I am not alone in this
>>> experience.  Some others have found that using local batteries instead of
>>> tying into the same batteries used by the motors has significantly reduced
>>> the noise, however in my case I am already using a separate battery
>>> isolated from the motor batteries.  Another choice that has seemed to make
>>> a difference is mounting an SB-1001 outside the hull and running the
>>> headset wires through the hull instead.
>>>
>>> Anyone else have similar experiences with OTS?
>>>
>>> Jon
>>>
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