Loading ...
Sorry, an error occurred while loading the content.
 

Re: VLF beginner.

Expand Messages
  • ssshoema
    Currently with the recommendations of the group I have switched from Mic input on on USB sound to line. Also denoiser is now off. Positive results are a lower
    Message 1 of 12 , May 1, 2013
      Currently with the recommendations of the group I have switched from Mic input on on USB sound to line. Also denoiser is now off.
      Positive results are a lower noise floor, a higher density of sferic/tweak activity, the ability to eliminate the use of denoiser in SL. I did have to initiate the P Nicholson hum filter in L4/5 and it seems to be working flawlessly.
      Negative results is a narrow peak centering at 6.2Khz that still needs resolving. This was present while using Mic input but not as narrow and strong.
      Overall recommendations thus far has made, in my opinion, a marked improvement in audio quality and sferic/tweak reception.
      You can view the spectrum at http://vlf.ssbwx.net to get an idea of what I am talking about.
      Thanks to the group!!
      http://vlf.ssbwx.net
      http://www.ssbwx.net:7777/VLF.mp3

      --- In VLF_Group@yahoogroups.com, Tom Becker <gtbecker@...> wrote:
      >
      > On 04/29/2013 08:46 PM, ssshoema wrote:
      > > Cat6, 40 feet, to the loop...
      >
      > Transformer(s) on the twisted pair? The least you should have with a
      > wired loop is an isolation transformer at the sound card Line input to
      > balance the pair and loop. Two transformers (an additional one at the
      > loop end of the twisted pair) might improve noise, too.
      >
      > If you have insufficient signal for the Line in, maybe you need more
      > loop area or turns, or make some gain with the transformers (e.g use a
      > 8:2kOhm instead of 1:1). You can also, though, add gain to the ADC
      > output in SL's L4/L5 amplifier, but it's better to find or make the gain
      > ahead of the ADC. What is the loop?
      >
      > Denoiser off. Eliminate the noise source, don't hide it.
      >
      > Tom
      >
    • Tom Becker
      ... That is pretty severe; it sounds like a high-Q filter. Also, what is the source of the ~1pps up at 15kHz? You are receiving spherics, certainly. Your
      Message 2 of 12 , May 2, 2013
        > ... peak centering at 6.2Khz...

        That is pretty severe; it sounds like a high-Q filter. Also, what is
        the source of the ~1pps up at 15kHz?

        You are receiving spherics, certainly. Your stream is about two seconds
        ahead of my Cape Coral and Joel's Sebring feed (via Paul's server), so
        putting them on opposite speakers makes pattern comparison pretty easy.

        You just need to get that peaking under control. You might try feeding
        some convenient low-impedance audio - a radio maybe, or a sweeping
        signal generator - instead of the loop to see if the peak is caused by
        the loop or downstream from it. Just for grins, try turning SLs filters
        off altogether briefly to see what happens. Hum will come up, of
        course, but does the 6kHz peak disappear, too? Maybe you have an
        inadvertent filter curve working?

        Tom
      • ssshoema
        With your recommendation went from Mic to Line input and did a step by step from antenna to soundcard. Checked/cleaned all connections. Installed 1:1 600 ohm
        Message 3 of 12 , May 5, 2013
          With your recommendation went from Mic to Line input and did a step by step from antenna to soundcard. Checked/cleaned all connections.
          Installed 1:1 600 ohm audio transformer.
          Peak is gone -- Also SNR is much better with some tweaking of line input level and L4/5 AGC and not trying to drive audio so hard with line input instead gaining with AGC. Sounds much better.
          Took my dunce hat off and connected to Cape Coral, Sebring, and my stream at the same time and realized that I was just trying to drive audio harder when spheric activity was low. I have tried to match as closely as possible the same "listening level" that the two Florida stations have. In comparison my noise level is still higher but not by much. Thanks for the tips...they worked.
          The 1pps at 15 is something I have been struggling to pin down since I have started. It is not constant, some days it's there, some it's not. I have gone thru my house and shut off everything electric one at a time with no success. I would suspect it is from an outside source.
          So as it sits from antenna to speaker, Degauss Loop, 40' CAT6, 1:1 audio transformer, Line In at 25%, 48000, SL Filter with notch on, denoiser off, L4/5 AGC at 25db gain and out. Of course my intent is to squeeze all I can so I will be fiddling with SL. As of today I have narrowed bandpass to help limit the 1pps at 15k.
          My next plan is to relocate the loop to a higher, clearer part of my yard. I had heard that wrapping it with foil also reduces noise???
          Also in SL on a loud spheric the notch filter seems to drop out and return leaving a "notch trail" after the spheric has occurred, any clues?

          Hey, thanks for the instructions, you have been of great assistance.

          Steve - AD4TH
          http://vlf.ssbwx.net


          --- In VLF_Group@yahoogroups.com, Tom Becker <gtbecker@...> wrote:
          >
          > > ... peak centering at 6.2Khz...
          >
          > That is pretty severe; it sounds like a high-Q filter. Also, what is
          > the source of the ~1pps up at 15kHz?
          >
          > You are receiving spherics, certainly. Your stream is about two seconds
          > ahead of my Cape Coral and Joel's Sebring feed (via Paul's server), so
          > putting them on opposite speakers makes pattern comparison pretty easy.
          >
          > You just need to get that peaking under control. You might try feeding
          > some convenient low-impedance audio - a radio maybe, or a sweeping
          > signal generator - instead of the loop to see if the peak is caused by
          > the loop or downstream from it. Just for grins, try turning SLs filters
          > off altogether briefly to see what happens. Hum will come up, of
          > course, but does the 6kHz peak disappear, too? Maybe you have an
          > inadvertent filter curve working?
          >
          > Tom
          >
        • Tom Becker
          ... 25dB L4/L5 gain sounds high to me. To see what the line input signal level looks like, attach the Time Domain Scope to L1 and turn it on. If you see a
          Message 4 of 12 , May 5, 2013
            > ... tweaking of line input level...
            > ... Line In at 25% [] L4/5 AGC at 25db gain...

            25dB L4/L5 gain sounds high to me. To see what the line input signal
            level looks like, attach the Time Domain Scope to L1 and turn it on. If
            you see a flat line you probably should add some front-end gain - either
            or both with a step-up transformer and more Line mixer gain. To get an
            idea of what the level is, turn on the Signal Generator, pick a
            frequency of your choice and a level of -10dB, and connect it via the
            SPDT switch to the L1 summer; you should see the generated tone in the
            scope with peak-to-peak amplitude of~+/-20000 units (of +/-32767). Turn
            off and/or disconnect the signal generator and adjust your line input
            gain so that the hum (assuming it dominates) is about the same level,
            giving you a headroom of 10dB. Assuming the hum dominates, after it
            has been notched you'll be left with a smaller signal that you can make
            up with L4/L5 gain as required. I no longer use Spectrum Lab for VLF
            but, as I recall, I used only 6dB L4/L5 gain to make up the loss of a
            pretty-extreme custom filter I used to minimize TWACS interference here
            - but I use a whip on a VLF-3, not a loop; your loop might produce a
            small signal.

            > ... Peak is gone...

            It is reduced, I agree, but it sounds to me like there is still a
            resonance that needs damping - and a remaining significant noise level.

            > ... wrapping it with foil also reduces noise?

            Yes, a grounded shield layer around the loop can help reduce noise - but
            make certain you leave an electrical gap somewhere in that layer or you
            will have produced a shorted turn that will reduce the loop sensitivity
            greatly.

            > ... on a loud spheric the notch filter seems to drop out and return
            leaving a "notch trail"...

            Yes, a common artifact of a digital adaptive filter which continually
            learns what to remove to produce the notch(es). You'll hear similar
            effects on most of the streams; in severe pops, a reverberating artifact
            seems to leave the filter first, preceding the processed spheric. One
            solution is a series of analog notch filters - or just a high-pass and a
            harmonic-tolerant ear - but the digital solution is otherwise so
            effective that we accept the artifacts. Another, ideal but probably
            impractical, treatment is to move to some place where there is no
            utility power available for many miles and, therefore, no hum filter
            needed; Antarctica, maybe.

            Your loop, though, probably has some directionality (its plane is
            vertical, yes?). You might try rotating it on its vertical mount to
            find an attitude that might reduce the hum (and, perhaps, help identify
            your 15kHz tick source).

            It sounds like you're making progress, Steve.

            73

            Tom
          Your message has been successfully submitted and would be delivered to recipients shortly.