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Re: [VLF_Group] Re: Balanced-Line Driver & Receiver

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  • Ned Lewis
    Hi Joseph, I ve used these for quite a few different circuits. For a long time I used the 555 version ( Also with a T bypass cap across Vcc and ground ). I
    Message 1 of 15 , Apr 1 7:12 PM
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      Hi Joseph,
      I've used these for quite a few different circuits. For a long time
      I used the 555 version ( Also with a T bypass cap across Vcc and ground
      ). I don't remember noticing noise in any of those circuits although I
      do remember noticing that the regulation on the rectified negative
      output of the 555 was not quite as stable ( we're talking 10ths of
      milivolts here ) than the positive supply, and if you feed it through a
      79xx voltage regulator there isn't a lot of current left over for use
      in dual supply op-amps. Not suitable for circuits that need to measure
      extremely tiny voltages.
      I moved to the 766 maybe four years ago because it was simpler and
      used fewer components. I've noticed the oscillator noise in circuits
      for VLF work and also in a couple of very sensitive detector circuits (
      I've also run across a similar problem with a chopper-stabilized op amp,
      but that was solved by changing the parts placement ). In my gyrator
      circuit, the tone was audible if I listened to the output. Once I
      identified this as a problem, I redesigned the power supply and didn't
      spend much time trying to learn much about it, but I did have the
      impression that the noise was being picked up via coupling between the
      766 chip and the input amp. I think don't think it was leaking though
      the output of the 766 or causing the positive supply to oscillate by
      changing the load. I remember wondering if a simple change in placement
      on the circuit board might not solve the problem, but the reciever
      worked so well after the change that I never pursued this ( I have a 200
      foot wire antenna, and catch all class C flares and about the top half
      of class B flares --- and there is very little 24 KHz noise at my
      location ).
      I'd be interested to know how well these problems can be solved,
      because the 766 sure is convenient! Now that I think about it... I
      was using 10 uF electrolytic caps to bypass that 766 circuit in the
      gyrator. I think of Tantalums as being stable with temperature and good
      for bypassing up into VHF. Still, I had the impression that the noise
      was coupling "though the air" in the enclosure.

      I'd like to mention again how much I appreciate this list for keeping up
      the enthusiasm and for lots of great ideas. If I hadn't been reading
      this list, I would not have tried running a couple of twisted pairs out
      to the pre-amp in my backyard.... too much of a gamble for the length
      and cost of wire involved. It works very well and I thank you all for
      the idea! I'm getting close to a very useable home listening setup for
      sferics.

      Ned


      Joseph DiVerdi wrote:

      > At 9:38 AM -0800 3/25/03, Ned Lewis wrote:
      > >Hello Group,
      > >
      > > Just a word of caution. I've used the 555- based negative supply
      > >and the 766 switched capacitor type negative supplies. With both I've
      > >had trouble with the oscillator causing interference. I have not tried
      > >to isolate the "negative converter" in a separate enclosure, and that
      > >might solve the problem. Nevertheless, this is a potential problem with
      > >this strategy for providing dual polarity DC...
      > >
      > > I was using a 766 type negative converter for my version of the
      > >Stoke's gyrator circuit.... and removing it made a *very* dramatic
      > >reduction in noise.
      > >
      > >Ned
      >
      > Ned, you are quite right that these switching power supplies can be
      > problematic. I should note that whenever I use a 555 in a circuit I
      > *always* put a 1uF tantalum capacitor *directly* between pins 8 and 1
      > (Vcc and Gnd). Not doing so is a no-no.
      >
      > Best regards,
      > Joseph
      > --
      > Joseph A. DiVerdi, Ph.D., M.B.A.
      > http://xtrsystems.com/ 970.980.5868 (voice)
      > PGP Key ID: 0xD50A9E33 970.224.3723 (fax)
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    • Ned Lewis
      I could definitely be wrong, but my impression is that the shielding is what did it for you. Mine is not well shielded, but since the circuit itself is not
      Message 2 of 15 , Apr 1 7:15 PM
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        I could definitely be wrong, but my impression is that the shielding is
        what did it for you.
        Mine is not well shielded, but since the circuit itself is not
        oscillating, I didn't worry much about it.

        Ned


        Richard Gagnon wrote:

        > When I built my Gyrator I considered the possibility of noise so I
        > equipped my
        > receiver with headers to quickly go from two nine volt batteries to
        > the 7662
        > and back with the 7762 disconnected and I saw no difference. I did
        > this for at
        > least a week while observing Cutler. I did this also with a 75 ohm
        > termination
        > on the antenna input, that is no outside antenna. When I built my
        > receiver I
        > decoupled with 10 ohm resistors in each chip power lead with the .1uf
        > cap,
        > 330uf cap on the + and - buss and I installed 3/4 inch high pc board wall
        > around the input chip that does the tuning. I made sure all leads to
        > input and
        > output, plus controls were all shielded. I also used a ground plane
        > around each
        > TL0-82. This might have made the difference. I am a strong believer in
        > shielding.
        > I am still in the learning stage but I did record the four flares a
        > couple of
        > days ago. I did not see the GRB.
        >
        > Cheers
        >
        > Richard
        >
        >
        >
        > --- Ned Lewis <ned@...> wrote:
        > > Hello Group,
        > >
        > > Just a word of caution. I've used the 555- based negative supply
        > > and the 766 switched capacitor type negative supplies. With both I've
        > > had trouble with the oscillator causing interference. I have not tried
        > > to isolate the "negative converter" in a separate enclosure, and that
        > > might solve the problem. Nevertheless, this is a potential problem
        > with
        > > this strategy for providing dual polarity DC...
        > >
        > > I was using a 766 type negative converter for my version of the
        > > Stoke's gyrator circuit.... and removing it made a *very* dramatic
        > > reduction in noise.
        > >
        > > Ned
        > >
        > > Richard Gagnon wrote:
        > >
        > > > Hello Group
        > > >
        > > > I have been using the ICL7662 for negative supplies. It only requires
        > > > two 10
        > > > ufd capacitors.
        > > >
        > > > Richard
        > > >
        > > >
        > > >
        > > >
        > > >
        > > > > The dual power supply is a nuisance but I have found the 555-based
        > > > negative
        > > > > supply generator to work well in a number of battery-powered or
        > remote
        > > > > situations.
        > > > >
        > > > > Best regards,
        > > > > Joseph
        > > > > --
        > > > > Joseph A. DiVerdi, Ph.D., M.B.A.
        > > > > http://diverditech.com/ 970.980.5868 (voice)
        > > > > http://xtrsystems.com/ 970.224.3723 (fax)
        > > > > PGP Key ID: 0xD50A9E33
        > > > >
        > > >
        > > >
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      • Joseph DiVerdi
        Dear Ned, ... Yep, while the current available with an inductor-based system is really good this one isn t too shabby if it s tweaked. I ve put some actual
        Message 3 of 15 , Apr 1 9:25 PM
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          Dear Ned,

          At 7:12 PM -0800 4/1/03, Ned Lewis wrote:
          >Hi Joseph,
          > I've used these for quite a few different circuits. For a long time
          >I used the 555 version ( Also with a T bypass cap across Vcc and ground
          >). I don't remember noticing noise in any of those circuits although I
          >do remember noticing that the regulation on the rectified negative
          >output of the 555 was not quite as stable ( we're talking 10ths of
          >milivolts here ) than the positive supply, and if you feed it through a
          >79xx voltage regulator there isn't a lot of current left over for use
          > in dual supply op-amps. Not suitable for circuits that need to measure
          >extremely tiny voltages.

          Yep, while the current available with an inductor-based system is really good this one isn't too shabby if it's tweaked.

          I've put some actual test data in a few images up on a temporary spot of my web site at http://xtrsystems.com/vlf/dc_power/ where a test circuit can be viewed together with some voltage-current and some efficiency curves. 150mA at -5VDC isn't too bad nor is 20mA at -8VDC (all with a +10VDC supply and over 50% efficiency).

          I like to use this circuit when I'm in a pinch or am resisting buying some more specialized part. ;)

          I haven't attempted a voltage tripler or quadripler to get the voltage up to the incoming positive rail but maybe I'll need to do it...

          > I moved to the 766 maybe four years ago because it was simpler and
          >used fewer components. I've noticed the oscillator noise in circuits
          >for VLF work and also in a couple of very sensitive detector circuits (
          >I've also run across a similar problem with a chopper-stabilized op amp,
          >but that was solved by changing the parts placement ). In my gyrator
          >circuit, the tone was audible if I listened to the output. Once I
          >identified this as a problem, I redesigned the power supply and didn't
          >spend much time trying to learn much about it, but I did have the
          >impression that the noise was being picked up via coupling between the
          >766 chip and the input amp. I think don't think it was leaking though
          >the output of the 766 or causing the positive supply to oscillate by
          >changing the load. I remember wondering if a simple change in placement
          >on the circuit board might not solve the problem, but the reciever
          >worked so well after the change that I never pursued this ( I have a 200
          >foot wire antenna, and catch all class C flares and about the top half
          >of class B flares --- and there is very little 24 KHz noise at my
          >location ).

          I'm not familiar with the 766 at all and will look into it. (Always like to learn about alternatives.)

          > I'd be interested to know how well these problems can be solved,
          >because the 766 sure is convenient! Now that I think about it... I
          >was using 10 uF electrolytic caps to bypass that 766 circuit in the
          >gyrator. I think of Tantalums as being stable with temperature and good
          >for bypassing up into VHF. Still, I had the impression that the noise
          >was coupling "though the air" in the enclosure.

          Could very well be. It's all so layout and application dependent which is why it is so important to actually build something *and* try to measure something to learn something.

          >I'd like to mention again how much I appreciate this list for keeping up
          >the enthusiasm and for lots of great ideas. If I hadn't been reading
          >this list, I would not have tried running a couple of twisted pairs out
          >to the pre-amp in my backyard.... too much of a gamble for the length
          >and cost of wire involved. It works very well and I thank you all for
          >the idea! I'm getting close to a very useable home listening setup for
          >sferics.

          You make a good point about the list - it's a good one, interesting problems, interesting solutions, interesting ideas, and interesting people.

          >Ned

          Best regards,
          Joseph
          --
          Joseph A. DiVerdi, Ph.D., M.B.A.
          http://xtrsystems.com/ 970.980.5868 (voice)
          PGP Key ID: 0xD50A9E33 970.224.3723 (fax)
        • Renato Romero
          www.vlf.it update: On the possible origin, propagation and detectability of ELECTROMAGNETIC PRECURSORS OF EARTHQUAKES by E. R. Mognaschi (upd Apr 2003) 73,
          Message 4 of 15 , Apr 2 11:33 AM
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            www.vlf.it update:

            On the possible origin, propagation and detectability of ELECTROMAGNETIC
            PRECURSORS OF EARTHQUAKES
            by E. R. Mognaschi (upd Apr 2003)

            73, renato romero
          • Herbert E. Plett
            ... I enjoy it. Looking at the circuit on your site I think of a question: -- if I put an extra cap in the line from pin1 to the lower diode (say just below
            Message 5 of 15 , Apr 2 5:57 PM
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              --- Joseph DiVerdi <diverdi@...> wrote:
              ...
              > I've put some actual test data in a few images up on a temporary spot of my
              > web site at http://xtrsystems.com/vlf/dc_power/ where a test circuit can be
              > viewed together with some voltage-current and some efficiency curves. 150mA
              > at -5VDC isn't too bad nor is 20mA at -8VDC (all with a +10VDC supply and
              > over 50% efficiency).
              >...
              > You make a good point about the list - it's a good one, interesting problems,
              > interesting solutions, interesting ideas, and interesting people.
              >
              I enjoy it.

              Looking at the circuit on your site I think of a question:
              -- if I put an extra cap in the line from pin1 to the lower diode (say just
              below the other cap), wouldn't that make for an (ground) isolated supply?
              (am I barking up the wrong tree?)
              -- should the bias be in the same direction, or the opposite one? assuming both
              grounds are fairly close or AC.



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            • Joseph DiVerdi
              ... Hmmm, that s an interesting question and I must admit that I don t know the answer. Best regards, Joseph -- Joseph A. DiVerdi, Ph.D., M.B.A.
              Message 6 of 15 , Apr 2 8:38 PM
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                >--- "Herbert E. Plett" <cachureos@...> wrote:
                >
                >I enjoy it.
                >
                >Looking at the circuit on your site I think of a question:
                >-- if I put an extra cap in the line from pin1 to the lower diode (say just
                >below the other cap), wouldn't that make for an (ground) isolated supply?
                >(am I barking up the wrong tree?)
                >-- should the bias be in the same direction, or the opposite one? assuming both
                >grounds are fairly close or AC.

                Hmmm, that's an interesting question and I must admit that I don't know the answer.

                Best regards,
                Joseph
                --
                Joseph A. DiVerdi, Ph.D., M.B.A.
                http://xtrsystems.com/ 970.980.5868 (voice)
                PGP Key ID: 0xD50A9E33 970.224.3723 (fax)
              • Peter.Schmalkoke@t-online.de
                ... That would make some kind of a DC insulated supply with the effective power transfer capacitance beeing the two caps in series and the effective audio
                Message 7 of 15 , Apr 3 3:43 AM
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                  Joseph DiVerdi wrote:
                  > > I've put some actual test data in a few images up on a temporary spot of my
                  > > web site at http://xtrsystems.com/vlf/dc_power/ where a test circuit can be
                  > > viewed together with some voltage-current and some efficiency curves. 150mA
                  > > at -5VDC isn't too bad nor is 20mA at -8VDC (all with a +10VDC supply and
                  > > over 50% efficiency).

                  Herbert E. Plett wrote:
                  > Looking at the circuit on your site I think of a question:
                  > -- if I put an extra cap in the line from pin1 to the lower diode (say just
                  > below the other cap), wouldn't that make for an (ground) isolated supply?
                  > (am I barking up the wrong tree?)

                  That would make some kind of a DC insulated supply with the effective power
                  transfer capacitance beeing the two caps in series and the effective audio
                  signal coupling capacitance between the left and the right side beeing the
                  two caps in parallel.

                  A second diode/capacitor network could also be used in order to provide a
                  positive supply which behaves symmetrical to the negative one. But a ground
                  insulation at audio frequencies would not be obtained this way.

                  If ground insulation is required then one could use a small transformer
                  (due to the high frequency) for the power transfer between the oscillator
                  and the rectifier section. That transformer should be made of a toroidal
                  core in order not to radiate a magnetic field to the antenna.

                  Peter Schmalkoke
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