<p dir="ltr">I suspect there is a problem with the shield of the transducer cable "floating" with respect to the hull.</p>
<br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Tue, Apr 29, 2025, 20:30 via Personal_Submersibles <<a href="mailto:personal_submersibles@psubs.org">personal_submersibles@psubs.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Send Personal_Submersibles mailing list submissions to<br>
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Today's Topics:<br>
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1. Re: OTS and motor controller noise<br>
(Alec Smyth via Personal_Submersibles)<br>
<br>
<br>
----------------------------------------------------------------------<br>
<br>
Message: 1<br>
Date: Tue, 29 Apr 2025 20:29:49 -0400<br>
From: Alec Smyth via Personal_Submersibles<br>
<<a href="mailto:personal_submersibles@psubs.org" target="_blank" rel="noreferrer">personal_submersibles@psubs.org</a>><br>
To: Personal Submersibles General Discussion<br>
<<a href="mailto:personal_submersibles@psubs.org" target="_blank" rel="noreferrer">personal_submersibles@psubs.org</a>><br>
Subject: Re: [PSUBS-MAILIST] OTS and motor controller noise<br>
Message-ID:<br>
<CABECYQ6ZWO=k9Jgk2pJWGOzNDfPX3U_oiZ=<a href="mailto:GyPXCpfbQqyGWuA@mail.gmail.com" target="_blank" rel="noreferrer">GyPXCpfbQqyGWuA@mail.gmail.com</a>><br>
Content-Type: text/plain; charset="utf-8"<br>
<br>
Just finished another round of experimentation. This is fun.<br>
<br>
1) Changing channels did absolutely nothing at all. All four were<br>
equally noisy.<br>
2) Turning on squelch was the opposite, it was so effective it completely<br>
eliminated the noise. There was not even minimal white noise and I wondered<br>
if the comms box was still on. However, I do not expect it to work that<br>
well in the water. I know I've tried it on dives and it was an improvement,<br>
but not to this extent. My guess is that it's because with the props<br>
spinning in air, thruster currents are drastically lower.<br>
3) Shielding with aluminum foil was super interesting. I could hear the<br>
attenuation go up and down just as I held a sheet of foil in my hand and<br>
moved it in and out of the space between one of the controllers and the<br>
comms box. D'you guys know what a Theremin is? Wrapping the OTS box in foil<br>
certainly did help attenuate the noise, but isn't a complete solution<br>
because of small gaps remaining, for instance for the cables. I'd say the<br>
noise reduction was probably 50-75%.<br>
<br>
Conclusion... I'll plan to both relocate the OTS box to the quietest area,<br>
and use squelch. Maybe get fancy by making an aluminum pocket into which<br>
I'll slide the SSB-2010, as a method of mounting it to the hull.<br>
<br>
Alec<br>
<br>
<br>
On Tue, Apr 29, 2025 at 4:46?PM Jon Wallace via Personal_Submersibles <<br>
<a href="mailto:personal_submersibles@psubs.org" target="_blank" rel="noreferrer">personal_submersibles@psubs.org</a>> wrote:<br>
<br>
> Alec, can you also test channel 3. I'm literally getting no interference<br>
> on Channel 3 which is 31.25khz upper side band. Using this channel would<br>
> be a good work around until an electronic fix can be achieved that protects<br>
> all channels.<br>
><br>
> Jon<br>
><br>
><br>
><br>
> On Tuesday, April 29, 2025 at 01:01:03 PM EDT, Alec Smyth via<br>
> Personal_Submersibles <<a href="mailto:personal_submersibles@psubs.org" target="_blank" rel="noreferrer">personal_submersibles@psubs.org</a>> wrote:<br>
><br>
><br>
> I happen to have my former sub Snoopy back in the shop because her current<br>
> owner has engaged me to recommission her. The job is about 99% done, and<br>
> the comms already installed, so I just conducted an experiment. I have the<br>
> same setup as Dave; SSB-2010 inside the cabin running on its own dry cell<br>
> batteries, connected to the transducer by a cable that is potted through a<br>
> penetrator without cutting. I had left that cable longer than needed, in<br>
> case the owner decided he wanted the OTS unit somewhere different.<br>
><br>
> I turned on the thrusters and started moving the OTS all around inside,<br>
> and also routing the cable along different paths. Here are the conclusions:<br>
><br>
> 1) As one would expect, there is much less noise when the thrusters are at<br>
> either zero throttle or full throttle. All the noise is in between, when<br>
> the signal is choppy.<br>
> 2) The noise is completely insensitive to the position of the cable. BTW<br>
> the cable I'm using was the OEM cable on another comms system similar to<br>
> OTS. It's a small diameter shielded single conductor, where the shield is<br>
> not grounded but used as a second conductor.<br>
> 3) Almost all of the variation in noise comes from proximity of the OTS<br>
> unit to the speed controllers. There is also a bit of noise if its placed<br>
> close to the battery cables, but it's nothing compared to the noise<br>
> emanating from the controllers.<br>
><br>
> So... the conclusion, at least in my case, is to place the OTS unit as far<br>
> from the speed controllers and battery cables as possible. David, does that<br>
> match the location of your OTS unit?<br>
><br>
> Best,<br>
> Alec<br>
><br>
> On Tue, Apr 29, 2025 at 12:54?AM David Colombo via Personal_Submersibles <<br>
> <a href="mailto:personal_submersibles@psubs.org" target="_blank" rel="noreferrer">personal_submersibles@psubs.org</a>> wrote:<br>
><br>
> Jon, youve got me thinking on this one. In the VAST, i have the diver unit<br>
> inside the sub, a continuous non cut cable potted to the thru hull<br>
> penetrator. The diver unit has its own 6 AA battery pack. With the pair of<br>
> 36v 101's, and wearing the headset, i have not had any issues with bleed<br>
> over noise. I am planning on adding the topside unit inside as a new comms<br>
> like you. My 101's are controlled by their own minnkota pwm which are on<br>
> the 36v lipo4 battery pack. The hotel loads are on their own 12v lipo4<br>
> battery pack, which is where i plan on connecting the topside unit. I will<br>
> run a test to see if i can find any signal interferance using the hotel<br>
> load battery vs its own 2-6v battery pack, and let you know what i find.<br>
><br>
> On Mon, Apr 28, 2025, 4:24?PM Alec Smyth via Personal_Submersibles <<br>
> <a href="mailto:personal_submersibles@psubs.org" target="_blank" rel="noreferrer">personal_submersibles@psubs.org</a>> wrote:<br>
><br>
> I've had mine to 250', but it was inside the sub. That said, the effect on<br>
> the audio quality was remarkable. It was perfectly clear, but if you ever<br>
> talked to your friends through a long garden hose as a kid, that was<br>
> exactly how it sounded. Which was great, because it made it feel spooky and<br>
> deep!<br>
><br>
> On Mon, Apr 28, 2025 at 4:35?PM Sean T. Stevenson via<br>
> Personal_Submersibles <<a href="mailto:personal_submersibles@psubs.org" target="_blank" rel="noreferrer">personal_submersibles@psubs.org</a>> wrote:<br>
><br>
> I have had a SSB-2010 a bit deeper than 130 as a diver without flooding<br>
> the housing, but I don't know how deep it will go without compensation.<br>
> That limit is the standard recreational diving depth limit for<br>
> no-mandatory-decompression-stop diving, and it is likely that it was both<br>
> designed and rated accordingly. These units have no helium speech<br>
> descramblers, so they are of limited utility for ambient pressure divers as<br>
> you go deeper. The donald duck voice on top of the limited bandwidth of<br>
> ultrasonic comms at all makes intelligibility a challenge.<br>
><br>
> I had the unit to ~165 fsw, and I suspect that you could push it deeper,<br>
> but you would void any warranty. I'm using PowerCom 3000D units now, and<br>
> these have similar depth ratings.<br>
><br>
> Sean<br>
><br>
><br>
> -------- Original Message --------<br>
> On 2025-04-28 10:59, Jon Wallace via Personal_Submersibles wrote:<br>
><br>
> SB-2010 is rated to 130 feet by OTS. Has anyone tested one to deeper<br>
> depths?<br>
><br>
><br>
><br>
> On Monday, April 28, 2025 at 01:15:01 PM EDT, hank pronk via<br>
> Personal_Submersibles <<a href="mailto:personal_submersibles@psubs.org" target="_blank" rel="noreferrer">personal_submersibles@psubs.org</a>> wrote:<br>
><br>
><br>
> Jon, put the whole unit outside the hull. I have zero issues with this.<br>
> I just put fresh batteries in for each dive<br>
> Hank<br>
> Sent from my iPhone<br>
><br>
> On Apr 28, 2025, at 10:16?AM, Jon Wallace via Personal_Submersibles <<br>
> <a href="mailto:personal_submersibles@psubs.org" target="_blank" rel="noreferrer">personal_submersibles@psubs.org</a>> wrote:<br>
><br>
> ?<br>
> Not a lot of room to work with of course inside the cabin. My controllers<br>
> are mounted up near the top of the hull, the coax comes in from the bottom<br>
> and is probably only about 18 inches laterally from the controllers. The<br>
> coax cable thru-hull is only 5/8 inch diameter (15.8 mm) so PL259's won't<br>
> fit through it to allow me removal for maintenance which is why I opted for<br>
> SMA. I suppose I could try it since I won't be removing the cable<br>
> regularly but it's definitely going to be a PIA change.<br>
><br>
> No I'm not sure whether the noise is electrical or acoustic in source but<br>
> now that you've asked I can tell you that the controllers make an audible<br>
> tone when the PWM is active, even with the OTS off. The tone changes of<br>
> course depending upon the PWM frequency I select, but it is always there.<br>
> The same tone comes out the OTS, but amplified.<br>
><br>
> Jon<br>
><br>
><br>
><br>
> On Monday, April 28, 2025 at 11:51:58 AM EDT, Sean T. Stevenson via<br>
> Personal_Submersibles <<a href="mailto:personal_submersibles@psubs.org" target="_blank" rel="noreferrer">personal_submersibles@psubs.org</a>> wrote:<br>
><br>
><br>
> Two things I would look at:<br>
><br>
> 1) Relative location and shielding between the motor controller and the<br>
> transducer cable. Is additional shielding (conduit?) possible?<br>
><br>
> 2) I have encountered problems in the past with noise on coax due to<br>
> impedance mismatch / partial signal reflection at any connectors. In my<br>
> experience, this is solved by moving from RG58 up to RG8, but you don't<br>
> have that option because the transducer is a potted assembly. If you have<br>
> enough cable tail available to experiment, I wonder about swapping the SMA<br>
> connectors for PL259 to see if that makes a difference.<br>
><br>
> Are you certain that the noise you are hearing is being introduced<br>
> electrically, and not acoustically in the ultrasonic range of the<br>
> transducer?<br>
><br>
> Sean<br>
><br>
><br>
> -------- Original Message --------<br>
> On 2025-04-28 06:47, Jon Wallace via Personal_Submersibles wrote:<br>
><br>
> Hey folks,<br>
><br>
> My OTS STX-101 receiver is picking up some fairly significant and annoying<br>
> electronic noise from my Roboteq PWM motor controllers. I tried changing<br>
> channels on the OTS hoping a different frequency might help but it didn't.<br>
> I also tried changing the controller PWM frequency between a range of 10khz<br>
> and 24khz but nothing between those frequencies made a significant<br>
> improvement. The noise is enough to override the normal squelch setting<br>
> but at the same time a strong communication signal through the OTS<br>
> transducer is enough to override the noise.<br>
><br>
> My configuration has the transducer outside the hull and receiver inside<br>
> the hull which required cutting the cable. I potted the cable in a<br>
> thru-hull and reconnected the cable inside the cabin with RG-58 SMA<br>
> connectors (soldered, not crimped).<br>
><br>
> In talking with a couple other folks it seems I am not alone in this<br>
> experience. Some others have found that using local batteries instead of<br>
> tying into the same batteries used by the motors has significantly reduced<br>
> the noise, however in my case I am already using a separate battery<br>
> isolated from the motor batteries. Another choice that has seemed to make<br>
> a difference is mounting an SB-1001 outside the hull and running the<br>
> headset wires through the hull instead.<br>
><br>
> Anyone else have similar experiences with OTS?<br>
><br>
> Jon<br>
><br>
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</blockquote></div>