[PSUBS-MAILIST] Personal_Submersibles Digest, Vol 136, Issue 29

Tue Apr 29 20:41:43 EDT 2025

I suspect there is a problem with the shield of the transducer cable
"floating" with respect to the hull.

On Tue, Apr 29, 2025, 20:30 via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

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>    1. Re: OTS and motor controller noise
>       (Alec Smyth via Personal_Submersibles)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Tue, 29 Apr 2025 20:29:49 -0400
> From: Alec Smyth via Personal_Submersibles
>         <personal_submersibles at psubs.org>
> To: Personal Submersibles General Discussion
>         <personal_submersibles at psubs.org>
> Subject: Re: [PSUBS-MAILIST] OTS and motor controller noise
> Message-ID:
>         <CABECYQ6ZWO=k9Jgk2pJWGOzNDfPX3U_oiZ=
> GyPXCpfbQqyGWuA at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Just finished another round of experimentation. This is fun.
>
> 1) Changing channels did absolutely nothing at all. All four were
> equally noisy.
> 2) Turning on squelch was the opposite, it was so effective it completely
> eliminated the noise. There was not even minimal white noise and I wondered
> if the comms box was still on. However, I do not expect it to work that
> well in the water. I know I've tried it on dives and it was an improvement,
> but not to this extent. My guess is that it's because with the props
> spinning in air, thruster currents are drastically lower.
> 3) Shielding with aluminum foil was super interesting. I could hear the
> attenuation go up and down just as I held a sheet of foil in my hand and
> moved it in and out of the space between one of the controllers and the
> comms box. D'you guys know what a Theremin is? Wrapping the OTS box in foil
> certainly did help attenuate the noise, but isn't a complete solution
> because of small gaps remaining, for instance for the cables. I'd say the
> noise reduction was probably 50-75%.
>
> Conclusion... I'll plan to both relocate the OTS box to the quietest area,
> and use squelch. Maybe get fancy by making an aluminum pocket into which
> I'll slide the SSB-2010, as a method of mounting it to the hull.
>
> Alec
>
>
> On Tue, Apr 29, 2025 at 4:46?PM Jon Wallace via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
> > Alec, can you also test channel 3.  I'm literally getting no interference
> > on Channel 3 which is 31.25khz upper side band.  Using this channel would
> > be a good work around until an electronic fix can be achieved that
> protects
> > all channels.
> >
> > Jon
> >
> >
> >
> > On Tuesday, April 29, 2025 at 01:01:03 PM EDT, Alec Smyth via
> > Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> >
> >
> > 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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