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Re: H-field receiver at Todmorden

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  • Peter, 54N 10E
    Hi Paul, Happy New Year! ... Ah, that explains the absence of Nulls . ... According to 4Front: It s possible to lock the sampling rate to the S/PDIF or world
    Message 1 of 56 , Jan 1, 2010
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      Hi Paul,

      Happy New Year!

      > > Direction?
      >
      > Varies. It's a 2-channel rx, there are two loops at right
      > angles.

      Ah, that explains the absence of "Nulls".

      > Or maybe there's a way to synchronise the
      > pair of M-Audio 192 cards that I'm using. Any suggestions?

      According to 4Front:
      It's possible to lock the sampling rate to the S/PDIF or world clock inputs by setting the envy24.sync setting in ossmix to SPDIF.

      See:
      sid@sid-fh: > ossmix
      Selected mixer 0/M-Audio Audiophile 192
      Known controls are:
      ...
      envy24.sync <INTERNAL|SPDIF> (currently INTERNAL)
      ...

      Other M-Audio cards (1010?) have a "World Clock Mode" input which can be used by OSS.

      The Kiel Longwave Monitor has moved to a new location, ~30km NW.
      The HBG-receiver works fine there. The broadband receiver still suffers from local interference sources and I'm trying to find a sufficient place for the antenna. Data uplink to the server is performed by UMTS now.

      Peter, 54N 10E (still)
    • Johan H. Bodin
      That reminds me of an unplanned experiment I did a few years ago. I was sitting in an open area in the forest listening to an E-field receiver and I found the
      Message 56 of 56 , Apr 20 5:49 AM
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        That reminds me of an unplanned experiment I did a few years ago. I was
        sitting in an open area in the forest listening to an E-field receiver
        and I found the hum level surprisingly strong as this location was about
        a kilometer from powerlines and houses. With the RX still grounded with
        a large screwdriver pushed into the soil, I rotated the RX and let the
        tip of the 1.5m whip antenna touch the wet ground in various directions.
        There was well defined "hum gradient" in the surface, two maxima ~180
        degrees apart and two minima at ~90 degrees to the maxima. The
        hum/sferics ratio also changed with this angle. I am quite sure that the
        signals I heard was indeed caused by "earth currents". When I tried this
        in some other locations, there was no distinct minimum to be found.
        Perhaps different current phase angle in different directions.

        BTW, this inspired me to try a stereo version with three ground stakes,
        one central stake for "common" and two "signal stakes" for left+right at
        90 degrees to each other (wrt the gnd stake). The signal stakes were
        about 10..20m from the gnd stake iirc. The sound did have some spatial
        effect. My first plan was to build a diff' amp' and use four stakes but
        I changed my mind when I couldn't foresee any common mode trouble that
        far from civilization.

        73
        Johan SM6LKM

        ----

        Paul wrote:
        > Made some tests today at a new antenna site which is three times
        > further away from the nearest mains. Used a 1 metre square
        > loop, about 100 turns straight into the mic input of the N140.
        >
        > Was hoping for a significant reduction of mains hum but the
        > levels are not that much different at the new site. Not what
        > I expected and quite disappointing.
        >
        > I wonder if, at the existing site, I am already far enough
        > away from the neighbourhood power lines and what I'm picking
        > up is actually the hum field from more distant sources.
        >
        > I tested two sites, one a fair way up the hillside, and another
        > lower down where the ground is more horizontal. The hum
        > there was lower. I wonder if the distant hum H vector is
        > oriented vertically and the hillside is distorting that to
        > give a horizontal component. The hum is much stronger in the
        > loop oriented across the hillside.
        >
        > Will try to make another test to see what angle H is to the
        > vertical. Perhaps I will have to tilt the loop away from the
        > hillside to null the hum.
        > --
        > Paul Nicholson
        > --
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