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Re: [VLF_Group] Re: Todmorden receiver

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  • Paul
    ... Sorry, I meant AD823. It s a dual op-amp and I only need one stage so I may as well run them in parallel to lower the noise. ... I ve been thinking along
    Message 1 of 18 , Nov 13, 2010
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      I wrote:

      > [new E-field front-end] uses a pair of AD797s in parallel in
      > the front-end,

      Sorry, I meant AD823. It's a dual op-amp and I only need
      one stage so I may as well run them in parallel to lower
      the noise.

      Johan wrote:
      > I have found hum currents in the ground,

      I've been thinking along the same lines. For a time I wondered
      if somebody nearby was returning some of their mains current
      to earth instead of neutral. But the smoothness of the daily
      amplitude variation convinces me that it isn't a single or local
      source.

      Of course, there will be ground currents anyway - induced by
      the incident field. The question is whether there's an extra
      non-induced component due to some wiring defect nearby.

      Wolf wrote:
      > During the last trip to the southern germany, I was amazed
      > to find the VLF hum / harmonics to be *much* lower there
      > than anywhere around here ...

      > In contrast to that, on a 'very remote' place in the hills
      > near Bielefeld ...

      My experience too. Taking a portable rx way out onto the
      moors, not a building or powerline in site, and the hum doesn't
      any less. I think I have to agree that the hum is a regional
      thing where a 'region' is something like 50 or 100km or so.

      Also, experience here is that the E-field hum is quite a bit
      less than the H-field hum, when both are compared with typical
      sferic amplitudes. The hum filter on the loop rx has to work
      a lot harder. I wonder why that is. Is that generally the
      case or just here? Soon I will have a calibrated E-field
      rx too and then we can look at the E/H ratio and see how the
      impedance compares with free space. I suspect it will be
      smaller than 377 ohms. The E-field and H-field hum don't go up
      and down in unison so that must mean we are in the near field
      of the source, which sets an upper limit to the source region
      and means that the E-field and H-field hum coupling are
      independent mechanisms.

      Peter wrote:
      > ...SAVNET/Brazil about loops at ground level. I was told that
      > they have decided using elevated loops only ...

      The lower leg of my rectangular loops runs along the ground.

      It would be nice to raise this but it would have to come up
      at least a metre and a half otherwise the sheep will just chew
      on it. There's about 1000pF capacitance between the loop and
      ground, hopefully spread evenly either side of the feed point.
      Grounding or floating the loop makes no difference to signals
      or hum. This C to ground will take advantage of any imbalance
      of the loop or poor CMRR of the amplifier. Hopefully this
      isn't a problem with the installation.

      It would be much more important to reduce the C-to-ground
      if the rx wasn't isolated from the domestic ground.

      I think I'll have to do some tests with a small loop.

      Changing the subject again... some time ago I mentioned having
      large phase angles between the loops, and also see quite large
      shifts in apparent bearing. For example GQD should be on 335
      degrees but often drifts east as far as 015 or 020 degrees.
      The effect is strongest on signals originating within a couple
      of hundred km. I've been reading and measuring and now
      understand the reason for this. It's simply a consequence of
      the mix of ground wave and sky wave. As well as being delayed,
      the sky wave undergoes quite a lot of rotation of polarisation
      when it is reflected, and the mix of this delayed and rotated
      signal with the direct wave gives the bearing shifts and large
      phase angles. There's much less bearing error and phase
      difference on distant signals such as NAA because they're
      arriving at quite a low angle anyway. The only other signals
      that I get virtually no phase angle on are locally generated
      test signals. So I'm sure now that this isn't some fault in
      the system.

      Beginning of the week I ordered parts from three suppliers,
      all next day delivery. Typically none have arrived so we
      wont see the new rx ready for another week. There's 200m of
      cable sat in a depot somewhere which I could really do with.
      By some fluke of evolution, small animals with sharp teeth
      just love cat5. Maybe they find the 18 volts quite tangy.
      --
      Paul Nicholson
      --
    • Jean-L. RAULT
      Dear all IMHO, the mains hum is everywhere, and at any time ... Please look at my attached ELF record showing 50Hz power lines, 82 Hz russian submarine
      Message 2 of 18 , Nov 13, 2010
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        Dear all

        IMHO, the "mains hum" is everywhere, and at any time ...
        Please look at my attached ELF record showing 50Hz power lines, 82 Hz
        russian submarine transmissions and US 60 Hz power grid
        ...
        This was recorded with an home-made E field receiver located t at 5km
        from the nearest 50 Hz power line.

        Jean-Louis F6AGR






        See attached , Le 12/11/2010 15:39, dl4yhf a écrit :
        >
        > Greetings all,
        >
        > Very interesting observations, thanks for the details Paul.
        >
        > Tom wrote:
        >
        >> I think the noise generated by dense population centers
        >> seems to extend more than 100km.
        > I can only second that. During the last trip to the southern germany, I was amazed to find the VLF hum / harmonics to be *much* lower there than anywhere around here (in northern germany).
        > The place is only a few hundred meters away from a village...
        >
        > 47°49'18.60"N 9°19'13.31"E ...
        >
        > but despite that the hum level was incredibly low (no audible hum at all).
        > In contrast to that, on a 'very remote' place in the hills near Bielefeld :
        >
        > 52° 7'14.51" 8°15'27.04"E ...
        >
        > it was impossible to find a place *without* hum, even deep inside the woods, with no signs of underground / overground cables. Also, during a long walk through the Teutoburger Forest, the hum level didn't change change (at least, not audibly).
        >
        > This also seems to confirm Johan's theory about long-range earth currents.... maybe the power system in southern germany is more 'balanced' (i.e. almost no earth currents) than here, near Bielefeld.
        >
        > All the best,
        > Wolf .
        >
        >
        >
        > ------------------------------------
        >
        > Post message: VLF_Group@yahoogroups.com
        > Subscribe: VLF_Group-subscribe@yahoogroups.com
        >
        > Members may request the option of receiving just one e-mail per day which contains all of the days comments. Simply send an e-mail to the list owner (VLF_Group-owner@yahoogroups.com) requesting digest mode.Yahoo! Groups Links
        >
        >
        >
        >
        >
        >



        [Non-text portions of this message have been removed]
      • Paul
        Hi All, Some alterations today to the E-field rx: two new isolating transformers, removed a gain stage and took out almost all the LP filtering to try to
        Message 3 of 18 , Nov 13, 2010
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          Hi All,

          Some alterations today to the E-field rx: two new isolating
          transformers, removed a gain stage and took out almost all
          the LP filtering to try to straighten out the phase response.
          Not quite there yet but a lot better. Response now to 96kHz
          through the M-Audio 192 at 24 bits per sample. It seems a
          bit cleaner at audio frequencies,

          Vorbis stream at http://67.207.143.181/vlf1.m3u

          I had to leave two poles of LP before the first op-amp, the
          intermod is chronic without. There's still just a little bit
          of intermod creeping through. Hopefully the AD823 will handle
          it better, but I've just heard they won't be delivered until
          6th December.

          Heard a couple of nice 2-hop whistlers in the last 20 mins.
          For some reason the whistler detector didn't catch them.
          Looks like the causative lightning was a hundred km or so
          out into the Atlantic, N/W of Ireland. It's not much of
          a storm but the whistlers were good. There's probably a nice
          duct right above us but without the lightning there's no way
          to detect it. This is where we need a radio amateur to be
          transmitting a suitably chirped beacon but there doesn't seem
          to be any interest. Might have to apply for a NoV myself to
          do the experiment but would have to find a tx site.

          PCs in the dog kennel are now thoroughly overloaded. Both are
          on their chinstraps with the extra load. A neighbour kindly
          offered to build me a customised equipment cabinet which is
          nearly finished - he's done a really nice job on it and it
          has room for another 2 PCs so that should solve that problem
          and I'll be able to run a camera again too.
          --
          Paul Nicholson
          --
        • Clive
          Dear Jean-Louis Grateful if you can give some details of your E-Field receiver. 73 s Clive GW4EYO
          Message 4 of 18 , Nov 13, 2010
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            Dear Jean-Louis

            Grateful if you can give some details of your E-Field receiver.

            73's

            Clive GW4EYO

            --- In VLF_Group@yahoogroups.com, "Jean-L. RAULT" <f6agr@...> wrote:
            >
            > Dear all
            >
            > IMHO, the "mains hum" is everywhere, and at any time ...
            > Please look at my attached ELF record showing 50Hz power lines, 82 Hz
            > russian submarine transmissions and US 60 Hz power grid
            > ...
            > This was recorded with an home-made E field receiver located t at 5km
            > from the nearest 50 Hz power line.
            >
            > Jean-Louis F6AGR
            >
            >
            >
            >
            >
            >
            > See attached , Le 12/11/2010 15:39, dl4yhf a écrit :
            > >
            > > Greetings all,
            > >
            > > Very interesting observations, thanks for the details Paul.
            > >
            > > Tom wrote:
            > >
            > >> I think the noise generated by dense population centers
            > >> seems to extend more than 100km.
            > > I can only second that. During the last trip to the southern germany, I was amazed to find the VLF hum / harmonics to be *much* lower there than anywhere around here (in northern germany).
            > > The place is only a few hundred meters away from a village...
            > >
            > > 47°49'18.60"N 9°19'13.31"E ...
            > >
            > > but despite that the hum level was incredibly low (no audible hum at all).
            > > In contrast to that, on a 'very remote' place in the hills near Bielefeld :
            > >
            > > 52° 7'14.51" 8°15'27.04"E ...
            > >
            > > it was impossible to find a place *without* hum, even deep inside the woods, with no signs of underground / overground cables. Also, during a long walk through the Teutoburger Forest, the hum level didn't change change (at least, not audibly).
            > >
            > > This also seems to confirm Johan's theory about long-range earth currents.... maybe the power system in southern germany is more 'balanced' (i.e. almost no earth currents) than here, near Bielefeld.
            > >
            > > All the best,
            > > Wolf .
            > >
            > >
            > >
            > > ------------------------------------
            > >
            > > Post message: VLF_Group@yahoogroups.com
            > > Subscribe: VLF_Group-subscribe@yahoogroups.com
            > >
            > > Members may request the option of receiving just one e-mail per day which contains all of the days comments. Simply send an e-mail to the list owner (VLF_Group-owner@yahoogroups.com) requesting digest mode.Yahoo! Groups Links
            > >
            > >
            > >
            > >
            > >
            > >
            >
            >
            >
            > [Non-text portions of this message have been removed]
            >
          • Clive
            Good Day All Whilst in UK and Europe power utility companies use either 2-wire single phase or 3-wire three phase HV distribution (50Hz) I observed a few years
            Message 5 of 18 , Nov 13, 2010
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              Good Day All

              Whilst in UK and Europe power utility companies use either 2-wire single phase or 3-wire three phase HV distribution (50Hz) I observed a few years ago when I was in the Merchant Navy, that in Korea (60Hz) they had single wire HV distribution system is some areas. Being single wire that required ground return. In my view not a good system. It certainly explained why in all the bars they had a variac transformer so as to adjust their voltage as their supply voltage varied according to load! I believe that there are similar single wire systems in USA which may explain a possible higher than expected 60Hz hum in Europe.

              73's

              Clive GW4EYO


              --- In VLF_Group@yahoogroups.com, "dl4yhf" <dl4yhf@...> wrote:
              >
              >
              > Greetings all,
              >
              > Very interesting observations, thanks for the details Paul.
              >
              > Tom wrote:
              >
              > > I think the noise generated by dense population centers
              > > seems to extend more than 100km.
              >
              > I can only second that. During the last trip to the southern germany, I was amazed to find the VLF hum / harmonics to be *much* lower there than anywhere around here (in northern germany).
              > The place is only a few hundred meters away from a village...
              >
              > 47°49'18.60"N 9°19'13.31"E ...
              >
              > but despite that the hum level was incredibly low (no audible hum at all).
              > In contrast to that, on a 'very remote' place in the hills near Bielefeld :
              >
              > 52° 7'14.51" 8°15'27.04"E ...
              >
              > it was impossible to find a place *without* hum, even deep inside the woods, with no signs of underground / overground cables. Also, during a long walk through the Teutoburger Forest, the hum level didn't change change (at least, not audibly).
              >
              > This also seems to confirm Johan's theory about long-range earth currents.... maybe the power system in southern germany is more 'balanced' (i.e. almost no earth currents) than here, near Bielefeld.
              >
              > All the best,
              > Wolf .
              >
            • Paul
              ... Yes, I think in Alaska and other places where population is thin. Single-wire earth-return is not good news if you re trying to receive VLF.
              Message 6 of 18 , Nov 13, 2010
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                Clive GW4EYO wrote:

                > I observed a few years ago when I was in the Merchant Navy,
                > that in Korea (60Hz) they had single wire HV distribution
                > system is some areas.

                > I believe that there are similar single wire systems in USA

                Yes, I think in Alaska and other places where population is
                thin. Single-wire earth-return is not good news if you're
                trying to receive VLF.

                http://en.wikipedia.org/wiki/Single-wire_earth_return

                Nothing like that in UK fortunately. Although sometimes a
                mean farmer will just run the live to an outbuilding and use
                a ground return. Once had a fault here on the farm where
                the current through the lighting circuit in a barn was returning
                to earth instead of neutral - caused a considerable potential
                difference between rx ground and domestic ground.
                --
                Paul Nicholson
                --
              • Tom Becker
                ... There might be the occasional out-building on a farm, but SWER distribution is uncommon here. You might recall in TWACS threads that the senior engineer I
                Message 7 of 18 , Nov 13, 2010
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                  > ... I believe that there are similar single wire systems in the USA...

                  There might be the occasional out-building on a farm, but SWER
                  distribution is uncommon here. You might recall in TWACS threads that
                  the senior engineer I spoke with at LCEC had never encountered one over
                  his career. The Alaska system was a demo that apparently did not yield
                  more installations. http://en.wikipedia.org/wiki/Single-wire_earth_return

                  Note that the image caption in the Wikipedia piece credits Canada.
                  Blame them.

                  Tom
                  http://www.ustream.tv/channel/bowcam
                  http://www.ustream.tv/channel/cape-coral-marine-radio VHF
                  http://67.207.143.181/vlf9.m3u VLF
                • Walter
                  Single wire is in wide spread use in Iceland for all those remote farm houses.
                  Message 8 of 18 , Nov 14, 2010
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                    Single wire is in wide spread use in Iceland for all those remote
                    farm houses.
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