75 MHz power line interference

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  • Thorbrandr
    Lieutenant Commander
    • Mar 2022
    • 124

    75 MHz power line interference

    What tips and tricks do people have for dealing with power line interference?

    My test beach has a few high voltage power lines overhead. At two spots under the lines, my R-class will stall if it is oriented the right way. This was a very repeatable thing. In one case the sub was perpendicular, in the other parallel to the lines. Happened 4 or 5 times in both spots. Turning the radio did not help.

    Note, I still have the short antenna wire on my receiver. it is about to get extended to a full wavelength. I'm adding a sealed silicon rubber rat tail (with the antenna wire inside it) to the WTC and laying the antenna along the length of the hull over the WTC.

    Any other suggestions?

    Thanks!
    Chris
  • redboat219
    Admiral
    • Dec 2008
    • 2735

    #2
    Go somewhere else...
    Make it simple, make strong, make it work!

    Comment

    • He Who Shall Not Be Named
      Moderator
      • Aug 2008
      • 12256

      #3
      Faraday Cage.

      David
      Who is John Galt?

      Comment

      • Das Boot
        Rear Admiral
        • Dec 2019
        • 1149

        #4
        Originally posted by Thorbrandr
        What tips and tricks do people have for dealing with power line interference?

        My test beach has a few high voltage power lines overhead. At two spots under the lines, my R-class will stall if it is oriented the right way. This was a very repeatable thing. In one case the sub was perpendicular, in the other parallel to the lines. Happened 4 or 5 times in both spots. Turning the radio did not help.

        Note, I still have the short antenna wire on my receiver. it is about to get extended to a full wavelength. I'm adding a sealed silicon rubber rat tail (with the antenna wire inside it) to the WTC and laying the antenna along the length of the hull over the WTC.

        Any other suggestions?

        Thanks!
        Chris
        A receiver is a receiver. Speakers or antennas. It’s picking up RFI you want to cure.
        Last edited by Das Boot; 08-29-2022, 01:33 PM.
        Of the 40,000 men who served on German submarines, 30,000 never returned.”

        Comment

        • Sam Victory
          Commander
          • Sep 2021
          • 391

          #5
          Replacing your single conversion RX with a dual conversion RX (either PPM or PCM), the 'DSP' filtering technology could perfectly handle the interference from the power source and the motors(brushed). If you only have the single conversion RX, try to add a filtering capacity to the spare channel of your RX, it could sightly work.


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          • Thorbrandr
            Lieutenant Commander
            • Mar 2022
            • 124

            #6
            Originally posted by He Who Shall Not Be Named
            Faraday Cage.

            David
            Wisconsin Energies would be displeased with my solution on those lines!

            Comment

            • Thorbrandr
              Lieutenant Commander
              • Mar 2022
              • 124

              #7
              Originally posted by redboat219
              Go somewhere else...
              in a land with many lakes, that is a consideration. However, this is a nice, clear, sand bottom swimming area, that I can go swim in as well. I have retrieved the R-10 from bad situations twice so far.

              Also, as a professional RF Systems Engineer, I am a bit stubborn. It needs to work where I want to go.

              Comment

              • Bob Gato
                Captain
                • Feb 2019
                • 826

                #8
                Try to eliminate long runs of metal like control rods if possible... use plastic (I am using plastic Sullivan cables) or carbon fiber especially the ends- metal to metal rod ends are problematic. They jiggle during usage and can cause glitching. I had a situation on my Atlantis boat where I went to touch a set screw on the rod end with a Allen key and it caused the servo to jitter.. I had a exact matching servo and rod end on the other side of the boat that would not do it. I changed out all the metal to metal contact to plastic.. everything's been rocksteady ever since. The long rods act as an antenna and they rebroadcast signals. Most of the time the glitching signal does not come from the overhead power lines it comes from something on your boat caused by reception and rebroadcasting.. and it might be as simple as cutting a long run of metal control rod and joining it with a plastic coupling (detuning)... Unfortunately it's all trial and error -good luck...BG
                Last edited by Bob Gato; 08-30-2022, 07:14 PM.

                Comment

                • Thorbrandr
                  Lieutenant Commander
                  • Mar 2022
                  • 124

                  #9
                  Originally posted by Bob Gato
                  Try to eliminate long runs of metal like control rods if possible... use plastic (I am using plastic Sullivan cables) or carbon fiber especially the ends- metal to metal rod ends are problematic. They jiggle during usage and can cause glitching. I had a situation on my Atlantis boat where I went to touch a set screw on the rod end with a Allen key and it caused the servo to jitter.. I had a exact matching servo and rod end on the other side of the boat that would not do it. I changed out all the metal to metal contact to plastic.. everything's been rocksteady ever since. The long rods act as an antenna and they rebroadcast signals. Most of the time the glitching signal does not come from the overhead power lines it comes from something on your boat caused by reception and rebroadcasting.. and it might be as simple as cutting a long run of metal control rod and joining it with a plastic coupling (detuning)... Unfortunately it's all trial and error -good luck...BG
                  Thank you. Will put that on the list after the antenna upgrade!

                  Comment

                  • roedj
                    Captain
                    • Sep 2008
                    • 562

                    #10
                    Originally posted by Thorbrandr

                    Note, I still have the short antenna wire on my receiver. it is about to get extended to a full wavelength. I'm adding a sealed silicon rubber rat tail (with the antenna wire inside it) to the WTC and laying the antenna along the length of the hull over the WTC.

                    Any other suggestions?

                    Thanks!
                    Chris
                    OK, here's the thing where we bring actual physics into the problem.

                    1. You say your antenna is short for a resonant antenna. You're correct. At 300/75MHz = 4 feet being a full wavelength at 75MHz. Here's the rub. That formula is ONLY good for a single element, straight wire antenna which is entirely in free space (= no conductors nearby). Any deviations from those conditions will result in an antennas being resonant at some other frequency. A single wire antenna rolled up in a ball (not a straight line) and stuffed into a WTC (which then adds both capacitance and inductance) which is then made to work under water (not free space) can hardly be said to meet those conditions either. What is the resonant frequency of such an antenna? Only God knows and God's not sharing the info.

                    2. But, IMHO, that's not the problem nor the solution either. Did you ever wonder why the RC receiver manufactures only attach a short wire to their product? It's my guess, and it's just a guess, that the system is not designed to use a resonant antenna but rather an active (non-resonant) antenna.

                    3. My best advice is to try anything but what you have now. Don't bother with a lot of calculations - they're probably way wrong anyway. Best of luck - you'll need it.

                    Captain Calculating

                    Born in Detroit - where the weak are killed and eaten.

                    Comment

                    • cheapsub
                      Lieutenant Commander
                      • Dec 2019
                      • 187

                      #11
                      what make and model of the transmitter and receiver?

                      AM vs FM

                      want to try 27MHz, 433MHz
                      2.4GHz?
                      Last edited by cheapsub; 09-01-2022, 08:58 PM.

                      Comment

                      • Thorbrandr
                        Lieutenant Commander
                        • Mar 2022
                        • 124

                        #12
                        Originally posted by cheapsub
                        what make and model of the transmitter and receiver?

                        AM vs FM

                        want to try 27MHz, 433MHz
                        2.4GHz?

                        FM, 75 MHz. Vex.

                        Would rather do lower hanging fixes than mess with new radios.

                        Don't want to mess with any HAM licenses.Also, availability is even worse than 75 MHz, which I have a good stock on for my projects. Like being able to run her 6 ft under, so no 2.4 GHz.Using that or a surface unit, however.

                        Chris

                        Comment

                        • Thorbrandr
                          Lieutenant Commander
                          • Mar 2022
                          • 124

                          #13
                          Originally posted by roedj

                          OK, here's the thing where we bring actual physics into the problem.

                          1. You say your antenna is short for a resonant antenna. You're correct. At 300/75MHz = 4 feet being a full wavelength at 75MHz. Here's the rub. That formula is ONLY good for a single element, straight wire antenna which is entirely in free space (= no conductors nearby). Any deviations from those conditions will result in an antennas being resonant at some other frequency. A single wire antenna rolled up in a ball (not a straight line) and stuffed into a WTC (which then adds both capacitance and inductance) which is then made to work under water (not free space) can hardly be said to meet those conditions either. What is the resonant frequency of such an antenna? Only God knows and God's not sharing the info.

                          2. But, IMHO, that's not the problem nor the solution either. Did you ever wonder why the RC receiver manufactures only attach a short wire to their product? It's my guess, and it's just a guess, that the system is not designed to use a resonant antenna but rather an active (non-resonant) antenna.

                          3. My best advice is to try anything but what you have now. Don't bother with a lot of calculations - they're probably way wrong anyway. Best of luck - you'll need it.

                          Captain Calculating
                          Wasn't trying for a resonant antenna per se.

                          Also made a bit of a units error. at 75.89 MHz, the wavelength is 3.95 meters, not feet. Alas this RF Systems Engineer read that as feet....I am used to working at much higher frequencies. Not used to working this low frequency stuff, hence my ask. Handling interference in the field tends to be a practical skill set based on experience with that band.

                          What was on the receiver was only about 0.4 meters. As you said: "A single wire antenna rolled up in a ball (not a straight line) and stuffed into a WTC (which then adds both capacitance and inductance)" is not ideal.

                          In general having at least a 1/4 wavelength is good, and more aperture generally doesn't hurt (there ARE exceptions to that!). I have added a meter to the antenna outside the WTC in a watertight tube, running the length of the sub over top of the WTC, and moved the receiver antenna lead off the motor and and other wires. Reception is already much better on the bench, but the real test will be when it goes in the water today.

                          Chris

                          Comment

                          • cheapsub
                            Lieutenant Commander
                            • Dec 2019
                            • 187

                            #14
                            Even the fly boys can't do much about it, on 72Mhz side. When it come to power lines.
                            you could try others receivers, like JR or hitec has some smaller dual conversion receiver. That works with the VEX/Futaba.
                            Should have get back to work on 27mhz stuff. Got the parts just need to hook it up.

                            Comment

                            • Thorbrandr
                              Lieutenant Commander
                              • Mar 2022
                              • 124

                              #15
                              Testing yesterday with the new antenna rig worked like a champ, right up to the point that the battery died! Got to go for a swim to pull her back in. One of the reasons I like that spot as it is a swim friendly area with sand bottom and only one sargasso sea area.

                              I had none of the glitchy behavior in the controls, and handling was much much better. NO leakage from he antenna tube and fittings.

                              Still need to tweak up the trim..from what I can tell the ballast tank is aft of the CG, so she goes from a a good surface trim to being tail heavy when submerged below periscope depth. Slowly making improvements.

                              Chrsi



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