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75 MHz power line interference

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  • #16
    I used aluminum foil too. Works like a Faraday cage.
    Of the 40,000 men who served on German submarines, 30,000 never returned.”

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    • #17
      Originally posted by Thorbrandr View Post

      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
      OMG. I am mortified that i didn't catch that too. A major senior moment - I'm 79 but I've been a HAM radio operator since I was 13. I can't believe I goofed like that. Keeps me humble - almost.

      Anyhoo, glad to hear you're having better luck with a different antenna setup.

      As a HAM, I operate on the 50MHz band - little competition at meets. I started buying up every Futaba 50MHz RF deck I could find about 5 years ago. With my 50MHz Sombra receivers, at my age it's a race to see who goes tits up first me or the electronics.

      Good thread - keep us informed.

      Captain Consternation
      Last edited by roedj; 09-03-2022, 10:10 PM.
      Born in Detroit - where the weak are killed and eaten.

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      • #18
        Originally posted by Das Boot View Post
        I used aluminum foil too. Works like a Faraday cage.
        Just curious. What exactly did you enclose inside your Al Faraday cage?

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

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        • #19
          Originally posted by roedj View Post

          Just curious. What exactly did you enclose inside your Al Faraday cage?

          Captain Curious
          My Honda generator made plug noise on my amateur radio gear while camping. I enclosed the spark plug housing with foil. Problem solved.
          Of the 40,000 men who served on German submarines, 30,000 never returned.”

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          • #20
            Originally posted by Sam Victory View Post
            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.


            V

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            what is int he picture you had? Thanks Chris

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            • #21
              Originally posted by cheapsub View Post
              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.
              Just found some 27 MHz gear. Can give it a try.

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              • #22
                Originally posted by Thorbrandr View Post

                what is int he picture you had? Thanks Chris
                Chris,
                that is simply a capacitor soldered to a connector. It is used to remove the glitching/twitching servos by cleaning up the power.
                peace,
                tom
                If you can cut, drill, saw, hit things and swear a lot, you're well on the way to building a working model sub.

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                • #23
                  Originally posted by trout View Post

                  Chris,
                  that is simply a capacitor soldered to a connector. It is used to remove the glitching/twitching servos by cleaning up the power.
                  peace,
                  tom
                  Interesting...still have some of that after the bigger antenna.....

                  where does it connect? Edited after rereading for content: to the spare channel on the receiver. Was assuming inline to a servo which is what I was expecting.
                  Last edited by Thorbrandr; 09-28-2022, 06:00 PM.

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                  • #24
                    Originally posted by Thorbrandr View Post

                    Thank you. Will put that on the list after the antenna upgrade!
                    Have you tried isolating the metal to metal connections yet-go down to the power lines, duplicate the jitter and disconnect control rods one at a time. This used to be a megahertz mantra with the airplane guys...and the fix will be easy enough if you find the offending culprit. To detune it could be as easy as putting a nylon rod clevis on it...

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                    • #25
                      Originally posted by Bob Gato View Post

                      Have you tried isolating the metal to metal connections yet-go down to the power lines, duplicate the jitter and disconnect control rods one at a time. This used to be a megahertz mantra with the airplane guys...and the fix will be easy enough if you find the offending culprit. To detune it could be as easy as putting a nylon rod clevis on it...
                      I think the extended antenna has taken care of most of it. Went from 18" of rolled up antenna stuffed in the WTC, on top of the rear push rods and brushed motor, to a full meter in a rubber tube outside the WTC. Only one clevis on a metal control horn, but there is metal to metal brass linkage in the stern.

                      In the last three runs I have had only two issues with non response on controls and both of those were at a lengthy distance.

                      Chris

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                      • #26
                        Great Chris if you're happy with the way it's operating don't change it..

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                        • #27
                          Originally posted by Bob Gato View Post
                          Great Chris if you're happy with the way it's operating don't change it..
                          I do have to ask... How did you increase the length of the antenna?... Did you solder on an extension to the 18-in stub that was original to the boat. In order to properly change an RC receiver antenna, the old antenna needs to be unsoldered from the receiver PC board and an exact specified length of antenna wire needs to be soldered in its place.... This wire might be silver plated strands, the number of strands and the gauge of The wire including the insulation (certain insulation types block radio waves)was intentionally specified by the manufacturer. All of these things factor into the tuning of your radio... There are charts on the internet that show the proper length for the receiver antennas at the frequency that you are using..

                          I did a walk test on my 1/64th gato 2 years ago and found that my 75 MHz radio continue to work fine to the point where I could not tell whether the submarine was pointing towards me away from me or sideways towards me... Megahertz radios should have a very long operational range.

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                          • #28
                            Originally posted by Bob Gato View Post
                            Great Chris if you're happy with the way it's operating don't change it..
                            right now yes, but tip filed away for later! Thanks!

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                            • #29
                              Originally posted by Bob Gato View Post

                              I do have to ask... How did you increase the length of the antenna?... Did you solder on an extension to the 18-in stub that was original to the boat. In order to properly change an RC receiver antenna, the old antenna needs to be unsoldered from the receiver PC board and an exact specified length of antenna wire needs to be soldered in its place.... This wire might be silver plated strands, the number of strands and the gauge of The wire including the insulation (certain insulation types block radio waves)was intentionally specified by the manufacturer. All of these things factor into the tuning of your radio... There are charts on the internet that show the proper length for the receiver antennas at the frequency that you are using..

                              I did a walk test on my 1/64th gato 2 years ago and found that my 75 MHz radio continue to work fine to the point where I could not tell whether the submarine was pointing towards me away from me or sideways towards me... Megahertz radios should have a very long operational range.

                              Normally I work with very very large antennas at much higher frequencies and some different element types. These 75 MHz range wire antenna beasts behave a bit differently...so practical advice is a help (thank you).

                              There is the theoretical side of things with getting maximum performance. I considered trying for a resonant tuned antenna, but there are some variables often missed in there (solder leads on PCBs, etc), and I don't have the details on the receiver PCB layout. Also, as was pointed out above, things get theoretically squirrely when you have a wadded up wire antenna anyways. I also did not want to risk a soldier issue on the receiver.

                              So, I simply tacked on a 1/4 wavelength for that channel to the existing wire. Slightly heavier gauge copper, normal PVC coating (not an issue for reception). Siilver soldered. Good joint. Shrink wrapped, and the end sealed just in case of leaks. Started easy - end connection. I considered a T but left that as a next step for a 1/2 wavelength antenna. Yes, there will be some minor effects from insertion loss at the solder joint, and I suspect some undesirable VSWR effects in that wire as well. I am certain it could be better.

                              The extended antenna is in a plugged silicone rubber hose on a nipple on the WTC. The new antenna wire lays straight along the top of the sub inside the hull with much better separation from the internal sources of interference and multi-path.

                              Signal reception is MUCH better. I have 2-3x the practical range, at least, and have not pushed it to the max yet. Jitter is down, although I will add a capacitor, and no more consistent dead areas under the power lines at my local put in.

                              Chris​

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