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  1. #51
    I get noise when my stepper motors enable. It affects my FM radio.
    Now.. I have no switches and all circuits etc in a metal control box. The noise is from my estop (un-screened cable in use).

  2. #52
    Quote Originally Posted by Voicecoil View Post
    The weirdest things can happen with EMC issues, at 6Mz a couple of bits of wire running parallel for a few m probably makes a half decent transformer
    This picture shows the output coupling transformer of a Marconi BD272 AM short wave radio transmitter rated at 250KW (that's a whole Megawatt peak output). I cut my teeth on these things in the 80's. All that power is being coupled through this single turn, air spaced transformer. These are the coils for 15MHz I think, but the 6MHz ones are not much bigger. The peak voltage across the primary turn is about 40KV even though it looks remarkably like a short circuit to the uninitiated.

    Click image for larger version. 

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    Quote Originally Posted by Voicecoil View Post
    No chance of that for me either - 'coz of the virus they've been shut here for over 2 weeks
    Same here. The local microbreweries are doing canned takeaways though, so I can still enjoy my favourite local brew at much less than the in-a-glass price they charge if you sit on an old wooden chair in their gravel yard getting swamped by midgies and other people's children. You have to look on the bright side!

    Western Australia has now closed it's borders to all non-essential travellers and travelling between different regions within WA without a good reason can cost you $50,000.
    Last edited by Kitwn; 06-04-2020 at 03:10 AM.
    Engineering is the art of doing for ten shillings what any fool can do for a pound.
    Wellington.

  3. #53
    Quote Originally Posted by Kitwn View Post
    This picture shows the output coupling transformer of a Marconi BD272 AM short wave radio transmitter rated at 250KW (that's a whole Megawatt peak output). I cut my teeth on these things in the 80's. All that power is being coupled through this single turn, air spaced transformer. These are the coils for 15MHz I think, but the 6MHz ones are not much bigger. The peak voltage across the primary turn is about 40KV even though it looks remarkably like a short circuit to the uninitiated.
    Click image for larger version. 

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    Thanks for posting that - awesome bit of kit even if it looks completely illogical to the uninitiated!

  4. #54
    Quote Originally Posted by Voicecoil View Post
    Thanks for posting that - awesome bit of kit even if it looks completely illogical to the uninitiated!
    This machine is 1960's technology. Some of the later, higher power designs, have water cooled the coils. A key difficulty with those was how to clamp the plastic water pipes onto the copper coils. Metal jubilee clips glowed white hot as soon as we switched the bloody thing on and plastic clips went brittle in about a week. We ended up using waxed cotton whipping cord, similar to to an old fashioned cricket bat handle. It's surprising the skills I had to learn as a BBC Transmitter Engineer back in the days when it was still fun.
    Engineering is the art of doing for ten shillings what any fool can do for a pound.
    Wellington.

  5. #55
    Quote Originally Posted by Kitwn View Post
    This machine is 1960's technology. Some of the later, higher power designs, have water cooled the coils. A key difficulty with those was how to clamp the plastic water pipes onto the copper coils. Metal jubilee clips glowed white hot as soon as we switched the bloody thing on and plastic clips went brittle in about a week. We ended up using waxed cotton whipping cord, similar to to an old fashioned cricket bat handle. It's surprising the skills I had to learn as a BBC Transmitter Engineer back in the days when it was still fun.
    Bet it made instant toasties. Seriously though, was all that RF energy hazardous to workers ?

  6. #56
    My standrad reply is "I've spent 40 years working in high RF fields and it nev, nev, nev, never did me any harm!" On one site I worked at you couldn't turn the flourescent lights off in the transmitter building. They wouldn't strike on their own but once lit they wouldn't go out until the maintenance break . They flickered in time to the program so you could set your watch by the lights: the time pips have a very obvious pattern.

    High power wireless has been around for a while now and the only known risk from such non-ionising radiation is the heating effect. VERY rare that anybody gets exposed to that kind of power, only antenna workers in practice. Contact with the conductors can give you an electric shock as well, but that isn't unique to RF.

    Some people claim to have been harmed by mobile phone use. A coleague of mine had a tumour the size of a tenis ball taken out of his head some years ago and it was on the side that he had a phone clamped to for half of the day, but there's no evidence that was the cause.

    Ionising radiation is the dangerous stuff but that's way above even the highest frequencies used for communications.
    Engineering is the art of doing for ten shillings what any fool can do for a pound.
    Wellington.

  7. #57
    Going back to the original topic, Kit, you don't have any transmitter masts near you ?

  8. #58
    Quote Originally Posted by dazp1976 View Post
    I get noise when my stepper motors enable. It affects my FM radio.
    Now.. I have no switches and all circuits etc in a metal control box. The noise is from my estop (un-screened cable in use).
    Have a look at that video Cube3 posted on page 1. Ferrite rings should help you there. You can wind the cable through the ring to increase it's effect.
    Click image for larger version. 

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    Engineering is the art of doing for ten shillings what any fool can do for a pound.
    Wellington.

  9. #59
    Quote Originally Posted by cropwell View Post
    Going back to the original topic, Kit, you don't have any transmitter masts near you ?
    Sorry, I missed this comment first time round:
    Actually, yes. As far as I'm aware it's the largest wireless transmitting antenna in the southern hemisphere and is about 14Km away from the CNC machine.
    Engineering is the art of doing for ten shillings what any fool can do for a pound.
    Wellington.

  10. #60
    Quote Originally Posted by Kitwn View Post
    Sorry, I missed this comment first time round:
    Actually, yes. As far as I'm aware it's the largest wireless transmitting antenna in the southern hemisphere and is about 14Km away from the CNC machine.
    It transmits VLF signals for the US Navy Submarine Fleet. I thought this could be giving your sensor LEDs a buzz. The sensors themselves generate an ac em field, but I don't know the frequency, but there might be some heterodyning.

    Just a thought, but it might have no merit.

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