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Re: MEG switching-Uwave switching info

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  • dtb1000@yahoo.com
    Stan, I looked at Digitoxin s and Dave Ball s schematics. It appears they are using FETs to switch, transistors are much faster. You have an LCR time constant.
    Message 1 of 7 , Aug 30, 2001
      Stan,

      I looked at Digitoxin's and Dave Ball's schematics. It appears they
      are using FETs to switch, transistors are much faster. You have an
      LCR time constant. You have to determine what you can do to reduce
      the time constant.

      A scope measurement should tell you what the 10% and 90% risetime of
      the waveform is.

      It appears that the path includes a diode which contributes to the
      time constant.

      DTB
      --- In MEG_builders@y..., "Stan Mayer" <StanMayer@c...> wrote:
      > --- In MEG_builders@y..., "Michael Couch" <cmichael_couch@h...>
      wrote:
      >
      > (Replies embedded in original message)
      >
      > > Stan,
      > >
      > > Sorry to be posting so often but...
      >
      > Yeah, you've been a busy guy today :-)
      >
      > > I think the answers you guys want about high speed switching were
      > posted in
      > > the JLNLabs egroup. Check the archive there back about a month
      > ago. Also,
      > > it was probably Russ Jones in there that posted the answers. He
      is
      > a
      > > lightwave engineer with MCI. He'll be glad to help.
      > >
      > > Michael
      >
      > Cool! David Ball will appreciate this info too. As I will be on
      > holiday for the next few days, I won't be checking on this for
      awhile
      > but I will, I am fairly certain. Gee whiz, I have been a busy boy
      > for the past week or so and I yam looking forward to truly resuming
      > MEG experiments.
      >
      > Best,
      >
      > Stan
    • dtb1000@yahoo.com
      The TL494CN has an output spec that states the pulse rise time falls between Min:=100ns and Max=200ns. A faster switching device isn t going to help unless the
      Message 2 of 7 , Sep 1, 2001
        The TL494CN has an output spec that states the pulse rise time falls
        between Min:=100ns and Max=200ns. A faster switching device isn't
        going to help unless the input pulse waveform is better than the
        current spec.

        DTB



        --- In MEG_builders@y..., "Stan Mayer" <StanMayer@c...> wrote:
        > --- In MEG_builders@y..., "Webdrifter" <webdrifter@o...> wrote:
        > >
        > > Tom Bearden is using semiconductor microwave switsching
        techniques
        > for switching the inputcoil of the MEG.
        > > Because of it's ease to control rise and decay times and fast
        > switching possibilities.
        > > What would I need best to do that?
        > >
        > > Webdrifter
        >
        >
        > Webdrifter,
        >
        > VERY good question for which I at least have no answer. David Ball
        > started to pursue this (and I watched with great interest) at our
        > site asking for help but he/we never really got any answers re: a
        > Microwave (aka, very high speed) SWITCHING device. I know that
        > companies like Hewlett Packard make very high speed transistors
        which
        > I think fall in the category of a Microwave switching device but I
        > haven't taken the time to research this at HP yet. An internet
        > search yielded nothing either except CATV switchers, which is a
        whole
        > other animal.
        >
        > Check messages along this line at this site starting with #141.
        >
        > Sorry that I don't have a quick and easy answer for you.
        >
        > Stan
      • Stan Mayer
        ... of ... DTB, I have used both MOSFET transistors and BIPOLAR transistors. The bipolars appear to be somewhat faster, sure. Re: Overcoming LCR time
        Message 3 of 7 , Sep 3, 2001
          --- In MEG_builders@y..., dtb1000@y... wrote:
          > Stan,
          >
          > I looked at Digitoxin's and Dave Ball's schematics. It appears they
          > are using FETs to switch, transistors are much faster. You have an
          > LCR time constant. You have to determine what you can do to reduce
          > the time constant.
          >
          > A scope measurement should tell you what the 10% and 90% risetime
          of
          > the waveform is.
          >
          > It appears that the path includes a diode which contributes to the
          > time constant.
          >
          > DTB

          DTB,

          I have used both MOSFET transistors and BIPOLAR transistors. The
          bipolars appear to be somewhat faster, sure. Re: Overcoming LCR
          time constant as something that needs to be done ... no kidding? ;-
          ) Probably the biggest time constant with "fets", is the D-S
          capacitance. Re: diodes contributing to times. Yes, Ball pointed
          that out to me some time ago so in my latest experiments have been
          testing without any diodes but results have been the same although
          without diodes, the circuit sort of feels better, if you know what I
          mean, as switching is quite clean.

          And my experiments to decrease rise and fall times have yielded (so
          far) improvements at least in rise times but no improvements in
          results. While at the moment I don't recall the exact numbers (see
          my notes in the files section and on my temporary web page) as I
          recall Tr ~=100 nsecs. and Tf = 1 usec.

          In closing, do you have any recommendations (p/n's and sources) for
          relatively inexpensive and readily available fast bipolars? I would
          appreciate SPECIFIC p/ns ... (it seems like everybody thinks I have
          all the time in the world to surf the web and find this stuff and I
          don't ;-) )

          Best,

          Stan
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