Help I get AC voltage through DTV coaxial cable from antenna

Discussion in 'Wireless & RF Design' started by dssence, Mar 13, 2010.

  1. dssence

    Thread Starter New Member

    Mar 13, 2010
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    HI guys I'm having a huge problem with this AC voltage I'm getting through the coaxial cable coming from my DTV Antenna.
    Everything started when I was going to plug my USB external hd to my computer, and I saw some little sparks on the metal shield of the connector. Then I was driving myself mad trying to figure out what's going wrong, I thought It must be the phases on my home circuit could be swapped or something like that like inverted fase or neutral.
    Till I used a tool like a screwdriver to check for AC voltage, I touched the metal shield of the male USB connector from my hard disk with one hand and with the other one I touched the female shield or the chasis of my pc case and the it lighted up. So there was AC voltage then I measured it with a digital tester and there was 0.4 volts AC. So then I disconnected the Coaxial cable from my DTV receiver and this AC voltage was gone.
    Odd thing is that if I make the same test touching the male usb conector with the tool to measure AC voltage and with the other hand I touch the metallic border of my window I get ac voltage as well. So I was thinking on doing an RF AC ISOLATOR ( do any of you have a simple circuit so I can do it myself I did ones with only caps about 10nf but I cannot see some channels I think cause it's filtering some frequencies) to place in the coaxial cable going to my DTV receiver but how the hell is AC voltage coming from the antenna if the antenna has no voltage feeding it. Hope you guys can help me on this cause I don't know what to do.
    I don't have a ground cable connection to connect my devices.. so all I got left is the way they are.
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    This is a common problem found here too.
    It's the voltage induced in the coax shielding that you are getting, the level will vary from a mere sting to a "WTF" :eek: shock..if you know what I mean ,:D the variation comes in humidity, the dampness of the ground, and also how dry the body of the victim.

    If you disconnect the cable then every equipment in the household earth will be at zero volts. Once the cable is connected the earth voltage rises. The loop comes from the antenna jack connecting to the body of the box or TV, which has no earth connection. I used to earth the cable box or the TV. and also use a better earthing for the main house supply. Better means to drive a separate earth rod with a cable deep into the ground where water is able to touch the rod. The wire should be used as the main earth for all the power outlets in the house.
     
  3. dssence

    Thread Starter New Member

    Mar 13, 2010
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    Hi R!f@@ thanks for your help, I still don't understand something, how on earth does the AC or potential flow through the coaxial cable, if the antenna is not feeded with any voltage. I'm asking this cause I did the test to disconnect the antenna from the receiver and there's no voltage. Yesterday I stayed waked up and played around with some creamic caps to make a filter to the coax and the voltage went away, but I couldn't see some channels, cause I guess the caps were filtering those super duper high frequencies some transponders trough stuff at. I think with an RF isolator it might solve this problem what do you think?.
    Aside from this I did the test to touch the metal shield of the male usb connector and with the other hand I touched the metalic border of my room window using a tool to measure AC voltage with is like a screwdriver which lights up, and I had voltage in my window? hows that possible could there be a voltage flow coming from somewhere onto the window.. this is completely independant to what's happening on the coaxial cable. I completely understand what you're telling me about poor grounding and that would be an effective solution, but there's no other way to avoid this ? I'm talking about the AC voltage on the coax, and about AC voltage in my Window .
    Something I would like to know and I always had a big doubt, is if this kind of voltage flow or potential going through my computer could affect it's stability as there are oscillators and other components. or It's some kind of myth.
    Once more thanks so much for your help ! big Hug! Paul :)
     
  4. retched

    AAC Fanatic!

    Dec 5, 2009
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    To you have large power lines near the window?
     
  5. dssence

    Thread Starter New Member

    Mar 13, 2010
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    Hi retched thanks for your reply, well not that I'm aware of , I'm in a residential neighbourhood, and power lines go under the earth. I asked
    R!f@@ , what could be the cause that when I use the test tool for AC voltage like a screwdriver on my window touching the usb male connector I get ac voltage. I really want to solve this firstly without adding a ground rod like R!f@@ told me which I know it's logical... but I feel there's something else going on here. Thanks once more for your help :)
     
  6. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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    It's the same type of effect as when you touch the input to an audio amplifier and get a buzz or hum.

    That's AC and electrical noise being picked up on your body, the antenna cable is doing the same thing.
     
  7. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I have seen the effect on old tv sets.
    In some of them the capacitor on the input of the antenna was not working correct.
    This could lead to a leakage current from the mains to the antenna connection.
    When you connected an antenna or pulled it you could see the sparks.

    Greetings,
    Bertus
     
  8. retched

    AAC Fanatic!

    Dec 5, 2009
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    The window is most likely not the source of the AC, it is probably noise emited from the GND. On your "screwdriver" probe, is it like a soldering iron with a light bulb in it and a ground cord with an alligator clip on the back?

    Do you have a digital multi-meter? Or any metered test equiptment?
     
  9. dssence

    Thread Starter New Member

    Mar 13, 2010
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    Hi guys thanks all for you replies,

    Retched, well I got a digital multi-meter and when I place it on AC scale under 200volts and I touch the PC chassis ground with the window DAMN!!! I GET 05.8 volts ! what the heck!! . That's a lot of voltage isn't it that like 58 volts??? AC !! This is completely independant from the coaxial cable voltage or it's linked to that problem as well?

    Hi Bertus ,

    What you said is that some device I got on my room its leaking current to the mains ? I'm asking you this case maybe " I mean MAYBE" some of the home mains cables maybe touching some piping dunno.. I honestly dunno why the window has AC voltage..

    hope you guys can help me out to make some tests.. and see what could be causing this.. Thanks again
    :)
     
  10. retched

    AAC Fanatic!

    Dec 5, 2009
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    Ok.. Are we 500% sure the meter isnt registering mV ? And do you have Lead crystal windows or something?
     
  11. dssence

    Thread Starter New Member

    Mar 13, 2010
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    Hi retched I checked the digital multimeter scale and it says

    ACV and there I get ... 06.1 under 200 ACV scale. by Mv you meant millivolts.. I don't think it's milivolts it's measuring volts in here.. but by 06.1 on 200 volts scale wouldn't that be 61 volts ac? . The windows here it's aluminnium .. I think .. but it's metal.. so it's conductive..
    I did check touching the pc chassis with one hand.. and with the other I use the srewdriver probe for AC voltage.. touching the windows.. and it didn't light up..so how could that be possible? wasn't lighting up.. and with the digital multimeter I get that reading..
    Retched thanks for your help once more. :) nice to know you guys are trying to help me out solve this.
     
    Last edited: Mar 14, 2010
  12. retched

    AAC Fanatic!

    Dec 5, 2009
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    No, 6.1 would still be 6.1. But check on the screen itself. It should add a 'm' if it is reading millivolts.

    I would be very scared if you had much voltage on the window sill.

    And until now, I thought you meant the glass, not the frame..jeez..
     
  13. dssence

    Thread Starter New Member

    Mar 13, 2010
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    Hi retched, I was taking a shower.. well I did check again. did the test and now it reads 1.6(no Mv meaning millivolts.. so it's meaning volts ) it seems it fluctuates depending the hour.. what could be going on? . And yes I am scared cause that's AC voltage on my window right.. I mean some ppl told me to ground the decoder to the frame of the window .. but I don't think that would be a good idea..
    thanks for helping me out, keep me posted. :)

    UPDATE: I realised something.. I got a window air conditioner those which are bigones not split. And when I turn it on the voltage rises to 3.0 AC , when it starts blowing cold air the compressor starts working rises to 5.1 - 6.1 and when it turn it off completely goes to 1.5 could it be there's a current leak from the air conditioner? and how on earth is the voltage going to the frame of the window.
     
    Last edited: Mar 14, 2010
  14. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    This phenomenon has been discussed in other forums as well ...

    http://forums.whirlpool.net.au/forum-replies-archive.cfm/446976.html

    I've had people complain to me about this. I was once compelled to take a video recording unit out of service [for OHS reasons] - even though it was OK from a standard electrical safety test perspective. It seems rather "common" and often relates to double insulated consumer electronic hardware devices which make extensive use of SMPS.

    I contacted the electrical safety regulatory authority in my state about this issue and while they are aware of the "problem" they can do very little about addressing it successfully - with the proliferation of imported hardware of this type. The 'genie' was 'out of the bottle' - so to speak.
     
  15. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Here's another reason
    Do your floor has tiles. And are you wearing any shoes.
    Tiled flow and bare foot grounds you much effectively, making you a better conductor to sense these kinds of leakage.
     
  16. retched

    AAC Fanatic!

    Dec 5, 2009
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    You shower? I gotta look into that. :)

    The window AC unit is case grounded. Compressors are very noisy (electrically speaking) You are putting a voltmeter in line measuring your ground potential. You are actually measuring the voltage that is leaving the unit, heading to ground. This should be on the order of very few milliamps at best. Are you using a 2 prong plug for you AC? Sometimes customers that have used a 3 prong to 2 prong adapter will have higher instances of ground noise.
     
  17. dssence

    Thread Starter New Member

    Mar 13, 2010
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    Hi guys thanks for all your answer, I didn't quite understand what's wrong with double insulated devices.. and switched mode power supplies as TNK said


    . I mean my DTV decoder has ony 2 connectors neutral and live. What I still don't understand is where is that AC voltage coming from the COAX antenna. Is that AC voltage coming from the satelite the dish is positioned? I know a small amount of milliwatts is sent from the Sats transponders.. .but I would find extremely weird if that was the case. Secondly well I don't have any tiles on my floor it's just carpet and I was wearing shoes. What I said about measuring AC voltage from the pc chassis and to the window frame while the Air conditioner unit was working I still don'tunderstand how I get those voltages going up and down.. seems to me like if there's some kind of voltage leak somewhere.. could be the reason.. Retched I'm using a 2 prong plug .. cause I don't have ground earth connection in this building.. so I suppose the Earth ground connection is not real earth, could that be the problem that the real ground connection should exist.. and that voltage instead of going and being discharge to ground ... cycles through the circuit? leaving that voltage I'm measuring? . Thanks to all of you guys. :)
     
  18. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    U r getting static discharge dude...
    Ground all the appliances properly before you blow up any thing
     
  19. dssence

    Thread Starter New Member

    Mar 13, 2010
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    R!f@@ you say it's static cause I said I had a carpet instead of a tiled floor?.. how do you know it's static .. and not some other kind of leakage? . And how am I supposed to ground all devices if I don't have ground conenction in my home mains ..?
     
  20. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    walking on carpet, rubbing on them, fury things will built up static.
    it will discharge when ever you touch a grounded object.
    If the appliances are grounded then they are safe.
    on the other hand the charged human is walking little taser :D.

    If you are walking on carpet and by any chance if you touch a semiconductor thingy, it will damage it..
    Always be sure to discharge oneself by touching an earthed metallic object, when you handle remotes or phones or pc, or any thing electronic.

    Try this : wear a fury coat and also put on some bugs bunny fury shoes and walk on the carpet dragging you feet very quickly for a few secs.
    This will build up static voltage on you.
    Next thing to do is go and very quietly touch some ones ear with just one pointed figure, really slowly, as the finger touches the grounded human, the static charge that was build up in you will discharge via the other person causing him or her to jump from a minor shock :D.
    Fun stuff....but dangerous to semiconductors :eek:
     
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