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Help in identifying the schematic symbol

Discussion in 'General Electronics Discussion' started by whompah, Oct 25, 2012.

  1. whompah

    whompah

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    http://electronics-diy.com/tx200.php
    [​IMG]
    Hello there, this circuit seems interesting and I wanted to simulate and construct it, but the problem is I do not know what do the 3 symbols in the circuit represent (1 in audio input, 1 in the middle, and 1 at the antenna). I have never come across with these symbols before.

    Can someone lend a little help here ? appreciate that :)
     
  2. CocaCola

    CocaCola

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    Apr 7, 2012
    The symbol on the input and output is a coaxial connector... Not sure why they have one in the middle, unless there is a secondary tap for some reason...
     
  3. whompah

    whompah

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    Apr 10, 2012
    Yes, in the middle part, the wire shouldn't be connecting to the ground. Middle part confuses me a lot :(
     
  4. CocaCola

    CocaCola

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    It's not, IMO it's showing that another 'connector' or take off could be installed at that point for some reason... If you do not require that take off, just consider it a non-connection like this...
     

    Attached Files:

  5. whompah

    whompah

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    Apr 10, 2012
    I see. THANK YOU VERY MUCH !!! :D
    I will try to simulate that now.
     
  6. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    The one in the middle might indicate a feedthrough through a metal shield wall between the two parts of the circuit.
     
  7. davenn

    davenn Moderator

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    My thoughts exactly, Kris

    very common in RF circuits to stop feedback. They have just represented it poorely

    Dave
     
  8. whompah

    whompah

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    Apr 10, 2012
    But in simulation, can I represent it this way ?

    [​IMG]

    And also, in constructing the circuit physically, 1st stage (modulator) and 2nd stage (amplifier) should be seperated from each other by a metal plate right, but physically connected by a wire without using co-axial cable as shown in the figure above ?
     

    Attached Files:

    Last edited by a moderator: Oct 26, 2012
  9. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    The circuit is probably meant to be constructed in a metal (steel) box or rectangular tube. The metal is the circuit ground. You place a steel sheet with a hole in it between the two sections of the circuit, and solder it to the metal on three sides (the fourth side is formed by the clip-on steel cover), and feed the signal through the hole, using insulation, or a ceramic tube, to insulate the wire so it can't make contact with the plate.

    You can also get complete feedthrough components that you solder to the hole, which have a connection on each side. Open up a TV tuner or modulator; you may see something similar.

    I haven't ever seen coax cable used for the feedthrough.
     
  10. davenn

    davenn Moderator

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    yeah, .... more commonly its just a semicircular notch cut out of the metal shiels so that the PCB track passes though

    Dave
     
  11. davenn

    davenn Moderator

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    yes simulate it that way as shown with no connections at those points :)

    as i said in my previous post, its normally just a PCB track passing through a notch cut out of the metal shield

    will see if I can find an example pic for you

    Dave
     
  12. davenn

    davenn Moderator

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    OK in this pic from my collection of RF gear, there are 2 places in the metal wall where the RF paths move from section to section....
    one on the bottom right and one on the left wall

    [​IMG]

    now just remember and for clarification....
    You CANNOT use feedthrough capacitors to pass RF. The whole idea of feedthrough caps is to stop the passage of RF
    In the image above there is a feedthrough cap on the right hand side metal wall bringing DC into that section. The feedthroough cap stops RF leaveing via the DC feedline


    cheers
    Dave
     

    Attached Files:

    Last edited: Oct 26, 2012
  13. CocaCola

    CocaCola

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    Apr 7, 2012
    A poor way to represent that on a schematic, although to be fair if it was for a repair manual or service manual representing the connection that way would have been obvious to the person upon first glance of the physical circuit, so in that case representation isn't all important...
     
  14. davenn

    davenn Moderator

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    Sep 5, 2009
    a metal screen is normally indicated by using a dashed line eg....


    [​IMG]



    Dave
     

    Attached Files:

  15. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    Now that's an RF enclosure! Very mil spec-esc. ;)

    Chris
     
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