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Re: [VLF_Group] Re: Telefunken pr761/4 antenna

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  • rinus nienhuis
    Hi John thanks for the reply. In the past i saw somewhere ...a big ferrite , such as these Telefunken , used for ULF and ELF i think using a active antenna in
    Message 1 of 5 , Nov 1, 2008
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      Hi John

      thanks for the reply.
      In the past i saw somewhere ...a big ferrite , such as these Telefunken , used for ULF and ELF
      i think using a active antenna in my situation , for below 15 kHz , making things much worse , <hum and city signals>
      this brought my to the idea of using this big ferrite of such low signals , maybe with different Capacitors <switchable>
      is it just a matter of counting the resonant frequency
      of both , the inductance <ferrite > and capacitance
      to get this narrow frequency
      or is there some kind of other rule , to get a certain portion of the band


      i got this device , 2nd hand , after putting my advertisement
      online for many years
      i was just very lucky
      i searched and searched but couldn't find anything on the antenna.
      if i read somewhere that someone has one i will let you know

      also my question about the rsdn station, which bandwidth to use, i hope someone replies

      regards

      rinus
      ----- Original Message -----
      From: John
      To: VLF_Group@yahoogroups.com
      Sent: Friday, October 31, 2008 4:33 PM
      Subject: [VLF_Group] Re: Telefunken pr761/4 antenna


      --- "rinus nienhuis" wrote:
      >
      > Hi Group
      >
      > Since last week i have a Telefunken PR761/4 Very Big Ferrite antenna
      > it is 73 cm long and there are 4 ferrites of 3 cm thick
      > Over the antenna is 1 thick winding
      >
      > can somebody say if this can be of any use for VLF, 0-15 kHz ?Maybe
      > in use with a capacitor?or something other?
      >

      Hello Rinus,

      I don't think you want to tune your coil with a capacitor unless you
      want to monitor a specific frequency, for example one of the Navy
      comm transmitters used by the SID monitoring community.

      Most of us use untuned, "active" antennas (loops or whips), which are
      naturally not as responsive as resonant antennas, but whose signals
      can be amplified with very hi-gain opamp circuits, and so have much
      greater band width.

      To go below VLF, into ULF/ELF (~100Hz or less), you will need many
      more turns of wire (thousands more). Then you could listen to the
      Schumann resonances and such. (Try the ULF-ELF Yahoo group for more
      info on this).

      Where did you get this device? (... and are there any more
      available? :-)

      John/AF4EX






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    • John
      ... In addition to using active antennas, we all tend to use Wolf Buescher s SpecLab program to view the signals. This is an audio spectrogram program which
      Message 2 of 5 , Nov 1, 2008
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        --- "rinus nienhuis" wrote:
        > i think using a active antenna in my situation , for below 15 kHz ,
        > making things much worse , <hum and city signals>
        > this brought my to the idea of using this big ferrite of such low
        > signals ,

        In addition to using active antennas, we all tend to use Wolf
        Buescher's SpecLab program to view the signals. This is an "audio"
        spectrogram program which uses the PC sound card as the front end.
        It's really a kind of "software defined radio" (SDR), because the RF
        signals that we're sniffing out overlap the 0-192Khz "audio" spectrum
        supported, more or less, by the sound cards.

        A conventional receiver would just amplify the signals and feed a
        speaker or headphones. But with SpecLab we can also "see" the signals,
        which includes very faint stuff that you can't hear, so I would
        definitely recommend this "SDR" approach to the VLF hobby.

        > ... maybe with different Capacitors <switchable>
        > is it just a matter of counting the resonant frequency
        > of both , the inductance <ferrite > and capacitance
        > to get this narrow frequency
        > or is there some kind of other rule , to get a certain portion of
        the band

        Again, you don't necessarily have to tune your coil to resonance.
        You'll get a much broader signal if you leave the self-resonant
        frequency above the signals that you're trying to hear. But they'll be
        a lot weaker, so you'll need some high-gain, low-noise circuits to
        overcome this signal loss.

        Your basic resonance formula is F = (1/2PI)*(1/SQRT(L*C)). The tricky
        part is computing L, since it not only depends on the effective area
        and number of turns, but also the permeability factor of your ferrite
        rods, which I assume is unknown. But since it's military gear I'd
        suspect it's very high, maybe 1000 or so. You'll just have to build a
        circuit and do some experiments.

        Here are some webpages with more info on using ferrite rods:
        http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/RadCom/part7/page5.html
        http://raylcross.net/murod_mm/

        ... and remember, when you get tired of those 75cm ferrite rods, just
        ship them to me. :-)

        John/AF4EX
      • rinus nienhuis
        John Again, many thanks for your help i will checkout SpecLab and the info on the links you gave Lots of friendly and helping people over here regards rinus
        Message 3 of 5 , Nov 1, 2008
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          John

          Again, many thanks for your help
          i will checkout SpecLab and the info on the links you gave

          Lots of friendly and helping people over here

          regards
          rinus
          ----- Original Message -----
          From: John
          To: VLF_Group@yahoogroups.com
          Sent: Saturday, November 01, 2008 2:05 PM
          Subject: [VLF_Group] Re: Telefunken pr761/4 antenna


          --- "rinus nienhuis" wrote:
          > i think using a active antenna in my situation , for below 15 kHz ,
          > making things much worse , <hum and city signals>
          > this brought my to the idea of using this big ferrite of such low
          > signals ,

          In addition to using active antennas, we all tend to use Wolf
          Buescher's SpecLab program to view the signals. This is an "audio"
          spectrogram program which uses the PC sound card as the front end.
          It's really a kind of "software defined radio" (SDR), because the RF
          signals that we're sniffing out overlap the 0-192Khz "audio" spectrum
          supported, more or less, by the sound cards.

          A conventional receiver would just amplify the signals and feed a
          speaker or headphones. But with SpecLab we can also "see" the signals,
          which includes very faint stuff that you can't hear, so I would
          definitely recommend this "SDR" approach to the VLF hobby.

          > ... maybe with different Capacitors <switchable>
          > is it just a matter of counting the resonant frequency
          > of both , the inductance <ferrite > and capacitance
          > to get this narrow frequency
          > or is there some kind of other rule , to get a certain portion of
          the band

          Again, you don't necessarily have to tune your coil to resonance.
          You'll get a much broader signal if you leave the self-resonant
          frequency above the signals that you're trying to hear. But they'll be
          a lot weaker, so you'll need some high-gain, low-noise circuits to
          overcome this signal loss.

          Your basic resonance formula is F = (1/2PI)*(1/SQRT(L*C)). The tricky
          part is computing L, since it not only depends on the effective area
          and number of turns, but also the permeability factor of your ferrite
          rods, which I assume is unknown. But since it's military gear I'd
          suspect it's very high, maybe 1000 or so. You'll just have to build a
          circuit and do some experiments.

          Here are some webpages with more info on using ferrite rods:
          http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/RadCom/part7/page5.html
          http://raylcross.net/murod_mm/

          ... and remember, when you get tired of those 75cm ferrite rods, just
          ship them to me. :-)

          John/AF4EX






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