[PSUBS-MAILIST] OTS and motor controller noise

Sun May 4 18:40:41 EDT 2025

 Thanks David.  It sounds like your tests confirm what others have said about using these units on their own internal batteries.  If you connect your STX-101 to an external battery with about 5-6 feet of wire you'll likely experience much worse results that match my experience.  One question about your controllers, were you testing with the minn-kota or Roboteq?
Using squelch with internal batteries is likely a good option for some of the channels.  With external batteries I could also attenuate the noise by using squelch but only with the setting at 100%.  The problem with using too much squelch is that it attenuates the incoming comms signal as well as the noise thereby diminishing the effective range of communications.  If the incoming signal from the transducer isn't strong enough to override squelch, you're not going to hear it.
The best solutions available to us are likely a combination of internal batteries, squelch, faraday cages, and filters.  If you can isolate your OTS into one of your VBT voids you are going to have a pretty good built-in faraday cage for it.  If you do end up connecting to an external battery, armored cables or metal conduit should help protect the wiring from EMI.  You have another advantage in that your Roboteq controllers are fully encased in a metal container and should vastly help contain EMI compared to my existing controllers which have a plastic cover.
Filtering is something I am investigating.  I believe we would benefit from an LC filter, and better yet a Pi LC filter.  I've got parts on order to fabricate one with a cutoff frequency of 1.5khz and am looking forward to testing it however I won't be able to do any more work on this OTS issue until the end of the month due to other commitments.  If somebody is inclined in the meantime, Amazon sells automotive noise filters for radios that may (or may not) work for our purposes.  They are cheap at $10-12 and readily available however I haven't found any that specify the cutoff frequency so it's a crap shoot as to whether they would suffice.  However, automotive noise is typically in the same range (8-20khz) so I think it would be a valid test.
This one has the best reviews I could find:https://www.amazon.com/Pipemans-Installation-Solution-Suppressor-Eliminator/dp/B07HZ4RSS7/

Jon

    On Sunday, May 4, 2025 at 05:21:33 PM EDT, David Colombo via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 Hi Jon, I've run some preliminary tests and the results are interesting. I'm going to rerun and try to document in better detail and frequencies. 
Here's my observations. To save me typing Topside unit =TS and Diver unit= DU. Ran the tests with the TU both sitting on my external fiberglass deck with the Transducer from the TU placed adjacent to my builtin transducer located externally at the rear of the hatch. Both Transducer cables are mfg full 25' cables with no cuts. Both TU and DU are on their own battery power. The DU is located on the starboard side, held with magnets onto the original VBT tank. Both Port and Starboard VBT have been cut open with a 16"x14" opening. Inside each of the VBT are located one PWM from MinnKota wired to the cutoff selector switch and then to the LiPo4 36v battery bank. Currently I have both the Minnkota speed selector switches adjacent to each other so they can lay over my knee to run the test. The DU is attached to my headset with channel set to 1, transmit: PUT, squelch on.  The TU was sitting on my feet inside the sub, speaker on, and I set the TU to the same settings except the squelch was set to off on the rotation dial. The TU is about 30" from either PWM.  With this setup I can hear my DU headset and the TU speaker at the same time.Test 1 with my DU only. Run each of the 4 channels through a series of starting out with one thruster and slowly running the speed scale in forward and then in reverse.Test 2 same test with both thrusters on and running the speed scale.  
Test 3 and 4 same test with the TU onlyTest 5 run both thrusters and both TU and DU.Note the DU is sitting closer to the PWM than the TU. TU is in its TU ABS case, with no additional shielding The thruster control cables are the mfg cables and I believe there is no shielding. 
Before I ran tests 1-5, I did a 6th test with  the transducer of the TU into the sub and placed it near the PWM units, and then again adjacent to the thruster speed control wires. 

In Test 6,I found  considerable frequency oscillation adjacent to the speed cable and less at the PWM units ( the PW units are incased in the mfg aluminum finned sealed case) all for channels (squelch off) I used this as a comparative baseline against the DU to see if Transducer proximity to the PWM made a difference and Initially I believe it does. 

So here are my observations:Test 1 & 2 DU: sometimes on start-up of a thruster I might get a short squelch burst and then no thruster noise for the rest of the speed scale. I believe that the DU which only has squelch on or off, is automatically compensating on all 4 channels, hence the reason I'm not getting any speed controller noise. No difference between test 1 & 2
Test 3 &4 TU: on all four channels with squelch off, there is a high frequency tone,  each different on the 4 channels and when on test 4 with both thrusters double the db of the frequency tone. No difference if I ran one thruster forwards and one in reverse at the same time.
Here is the interesting part: on each of the 4 channels there is a point on the squelch dial where you can eliminate the tone. approximately 25% on channel 1, 50 % on channel 2, 75% channel 3 and 100% on channel 4.  So if I am using channel 1, preset the squelch to 25% +/- and you're good to go, same with the other channels. The other interesting thing is the proximity of the TU  to the PWM. Outside the hull and about 3ft away from the PWM the intensity of the Tonal variation is substantially less, which might imply that additional shielding around the electronics of the TU could improve the reduction of the tonal frequencies. As I am planning to place the TU in the sub into one of the VBT with 1/2" thick steel on three sides, I'm hoping that will be enough shielding, only time will tell. Also I'm going to add some additional shielding on the thruster speed control wires  based upon the test results of test 6.When I rerun the test, I will data log the frequency of each channel and try to calibrate the squelch position for the TU.Any thoughts on how best to filter out frequency noise besides the squelch?  Anyway these are my current observations and I hope they give some insight into how to solve your problem.

Best Regards,
David Colombo

804 College Ave
Santa Rosa, CA. 95404
(707) 536-1424
www.SeaQuestor.com

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