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Hum suppression/elimination in apartments

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  • Siddhartha Jain
    After running a few tests, seems like it is AC interference after all. I took the antenna away from the apartment and all noise disappeared. Brought it back
    Message 1 of 48 , Apr 1, 2009
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      After running a few tests, seems like it is AC interference after all.
      I took the antenna away from the apartment and all noise disappeared.
      Brought it back into the apartment, turned off all appliances and
      unplugged all cables. The hum noise was still there. I could not turn
      off mains but with everything off and cables plugged out from wall
      sockets, the hum was strong as ever :(

      I tried to ground the antenna by connecting one end of the loop
      antenna to the metal railing on the deck that runs for about four
      stories. That did not help matters either.

      What next can I try to reduce/eliminate hum? Moving away the antenna
      away from the apartment is not an option given the very limited real
      estate, I have.

      Thanks,

      - Siddhartha


      On Mon, Mar 30, 2009 at 1:50 PM, Siddhartha Jain
      <siddhartha@...> wrote:
      > Thanks All. First, I will test the setup far from civilization to
      > ensure everything is alright with the antenna and sound card. Then I
      > can bring it back into the apartment and do device by device
      > elimination.
      >
      > - Siddhartha
      >
      > On Mon, Mar 30, 2009 at 7:21 AM, MarkD <mdennisond@...> wrote:
      >> I agree these dimmer switches are a right pain, I will be fitting a standard
      >> switch soon, when I have my dimmer on the harmonics are right up to the
      >> beacons.
      >>
      >> Also laptop psu causes interference & I've found also when I have my other
      >> laptop switched on there's interference coming from that also & I'm sure
      >> it's from the lcd screen inverter.
      >>
      >> The laptop I use at the moment for my stream, I have had to connect the dc
      >> output ground of the laptop psu to my radiator thus grounding it to stop the
      >> interference from it, the interference from it is awful without grounding
      >> it.
      >>
      >>
      >>
      >> Mark
    • jcal1001
      Congratulations Edgar on the performance of your unshielded indoor loop. I must say that yours is an exception to the rule on several fronts. One of the
      Message 48 of 48 , Apr 4, 2009
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        Congratulations Edgar on the performance of your unshielded indoor loop. I must say that yours is an exception to the rule on several fronts. One of the purposes of an electrostatic shield is to maintain balance to ground and to any nearby objects. With a proper shield the capacitance to ground and to any nearby objects will be the same in all parts of the loop no matter the orientation of the loop. Without a shield there will be a non-uniform current distribution around the windings so that the current induced in one turn will not be exactly in phase with the current induced in another turn. This degrades the performance of the loop.
        John



        --- In VLF_Group@yahoogroups.com, "Edgar" <fmpup@...> wrote:
        >
        >
        >
        >
        >
        > Hi Guys, I just had a "duh" moment and finally realized what that
        > post, about it being inconsiderate to simply hit "reply" and repeat
        > everything that's already been seen by everyone, meant. Here's the post,
        > the way it should be:
        >
        > I'm in a single family home, but the situation should be similar to an
        > apartment. I got reasonable results indoors by using a 12"(30cm) square
        > loop of about 30 turns. I forced the 8 ohm winding of a Radio Shack
        > 273-1380 audio transformer into a balanced low-Z input by connecting a
        > 51 ohm resistor from each end to ground. Note that the resistors also
        > damp out supersonic resonance to reduce interference pickup because
        > ultrasonics can intermodulate into VLF
        > frequencies. The 1 K ohm winding then drives the first op amp in the
        > receiver. The impedance of the loop is low enough to make it rather
        > insensitive to electrostatic interference, therefore no shield is
        > needed. The relatively compact size of the loop permits it to be
        > placed in a magnetic-hum quiet place indoors. A central location
        > indoors, away from current carrying wiring, CRT monitors/TV's, and major
        > appliances can be quiet enough to hear surprisingly distant(1000 miles
        > out for me) sferics, when using hi-pass filters that drop sharply below
        > 1000hz. That's what I found in my experimenting. Edgar
        >
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