Noise cancellation

Discussion in 'General Technical Questions and Answers' started by KP4SX, Jul 12, 2019 at 3:08 AM.

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  1. KP4SX

    KP4SX XML Subscriber QRZ Page

    Trying to help a friend with a bad electric line noise problem.
    He has built the VK5TM canceller and it works as advertised. Problem is too much cancellation of the desired signal as well. I suggested he needed a small puny antenna that would receive the noise much more than the desired signal. The offending HT line only runs about about 10ft away from his second-story roof and his real antenna is about 30 ft away.
    I suggested placing the noise antenna as close to the offending line as possible.

    Hoping that's enough introduction...what would be the 'best' antenna configuration for receiving the noise and being poor with received signals? A few feet of wire laying on the roof? Some sort of directional loop?
     
  2. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    NH7RO and N0TZU like this.
  3. WA7ARK

    WA7ARK Ham Member QRZ Page

    I tried a noise canceller, and concluded that the noise antenna must be small, but tightly-coupled to the noise source, while the receiving antenna must be as far away from the noise source as possible, with excellent common-mode blocking along the receiving antenna feed-line.
     
  4. KD0CAC

    KD0CAC Ham Member QRZ Page

    I think the 1st thing to do with noise is to - eliminate the source .
    In this case contact the power company and tell them , probably something going bad with there gear , insulator etc. they do not like there gear going bad , noise being the 1st indicator of an issue .
    If you can find the exact source , you may get better service .
    Remember polarization of signals , same vertical / horizontal for signals you want the closer they are - line of site , not so much for distant HF etc.
    Perpendicular for the ones you don't like .
    So do not run a dipole parallel to the power lines - especially if the are making noise .
    But still call the power company .
     
    K7TRF and KA0HCP like this.
  5. KP4SX

    KP4SX XML Subscriber QRZ Page

    Long story but this isn't in the USA. They haven't offered any more than a shrug to the complaint.
     
    KD2ACO, KM1H and NH7RO like this.
  6. WA4ILH

    WA4ILH Subscriber QRZ Page

    Maybe think about a magnetic loop receive only antenna. There is a post started on this under the low band VLF (sic) catagory below. I borrowed a magnetic loop from a friend and was amazed. Sadly, I had to return it after a week.
    Tom WA4ILH
     
  7. W8AAZ

    W8AAZ Ham Member QRZ Page

    IT seems to me that vertical antennas pick up manmade noises better than horizontal so I would try a vertical whip. Maybe collapsible type so that it can be set to the optimum length for picking up the local noise but not sigs.
     
  8. K8JD

    K8JD Ham Member QRZ Page

    Why not track down the source of this noise,?
    If it is the local utility companies, you have to find out where to send a complaint to, and know the location where the noise is worse.
    Use a portable receiver to run down the peak noise location .
    Work with a Radio club in your locale and see if others have worked on noise hunting.
    If the first try contacting the utility fails you have to go up higher than a receptionist who just answers the phone.
    Get into the engineering department and tell them they are loosing money when the power just arcs to ground, the bean counters would not like loosing money and you can help THEM !
     
  9. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    The noise sense antenna should be of the same polarization as the tx/rx antenna.
     
  10. G3YRO

    G3YRO Ham Member QRZ Page

    The problem is that Noise Phasing Units are only any good at nulling out noise from a point source . . .

    Noise from a Power Line will be radiating from all along the line, and so is like multiple sources. So I doubt if you will be able to null it out effectively (regardless of what noise antenna you use).

    The biggest noise source here in Britain is currently from Broadband Internet sent to houses using the old overhead telephone lines. Again, a noise phasing unit does nothing to get rid of it.

    What CAN make a big improvement is to use a small Receiving Loop. They're not usually that directional on signals, but they have a sharp null. So you rotate the Loop to null out the noise, and leave it set in that position.

    I have a homebrew one in my loft for DX-ing on 160m - details here:
    http://rogerkennedy.co.uk/g3yro/160mrxloop.htm

    Roger G3YRO
     
    K7TRF likes this.

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