Connect with us

Building Coaxial transmission line on PCB?

Discussion in 'Electronic Design' started by Geronimo Stempovski, Feb 12, 2007.

Scroll to continue with content
  1. Uwe Hercksen

    Uwe Hercksen Guest


    well, if the transmission line is very, very short.....

  2. Uwe Hercksen

    Uwe Hercksen Guest


    look here for FR408

  3. John  Larkin

    John Larkin Guest


  4. werty

    werty Guest

    work. I can imagine that John J. may well also. When you're aiming

    Its all theory . If its open , the RF will leak
    out . Like the holes in a MicroWave dish
    10:1 SWR , open lines ,
    and NO radiation .
    Transmission lines repulse , but that
    does NOT mean magnetic fringing
    and sending mag flds everywhere .

    Study CAT5e Ethernet cable .
    garbage !
    USB cables are much faster .

    I think ppl limit themselves to
    whats avail in PCB , then complain
    when it dont work , but if they'd
    experiment , they'd find the problem
    is using thin PCB .
    Then they limit on putting down
    100 transmission lines per mm .
    You cant learn , unless you experiment.

    you can't choke the dimensions
    and get good results , a transmission
    line needs exact dimensions , or you
    lose .

    In coax for 2.5 Ghz , for example ,
    it WILL have a large diameter and
    the center will have an exact dia and
    ratio .. No substitutes .

    Sending signals that will be amplified
    use high Z ( ~65 ohms ) and
    sending power needs low Z .
    These rules can't be bent .
    Thats what you're doin , is bending
    rules ...

  5. werty

    werty Guest


    You are hoping that we believe switchers
    cause lots of noise ....

    Zero ripple is what switchers do !
    The sudden pulse of current is only
    around a very short loop , it does
    not cause noise .
    They dont even have "ground loops"
  6. Hi John, I'm trying to compare several loss tangent values (I think that's
    the decisive parameter..!?) from several materials, FR4-, PE, etc. over the
    frequency. But it's hard to find such diagrams.
  7. MassiveProng

    MassiveProng Guest

    We cannot use switchers to feed to rails on our 2 to 12 GHz designs.
    NOISE CAN AND DOES get injected into such systems BY SWITCHING POWER

    YOU may not be aware of it, but those of us that work in such bands
    are aware of high frequency switching noise, and it DOES show up under
    spectrum analysis.

    Your brain has a ground loop.
  8. Shite man, what are you using for a computer, a 40-column
    Commodore PET?

    Even a PET wouldn't explain the random indentation.
  9. And the random word and punctuation spacing. Some kind of mobile
    phone? The Microsoft Word Usenet Export Filter?

    I think it's the usenet equivalent of green ink.

  10. John  Larkin

    John Larkin Guest

    No, what are you trying to *do*? WHY do you want a "coax on a pc

  11. I love it! I'd never heard the phrase "green ink" before. It's
    a keeper.
  12. John Larkin

    John Larkin Guest

    Never heard of micro hardline, I guess. Or non-TEM propagation modes
    in large-diameter coax.

  13. John Larkin

    John Larkin Guest

    Please post the schematic of a zero-ripple switcher.

  14. Ah, okay, what I am actually trying to find out is what makes FR4 act worse
    than e.g. teflon at data rates beyond 2,5 Gbps. Is it the loss tangent or
    the epsilon r? How is the frequency-dependent attenuation physically
    describable? Where does the energy go? Heat, ...? It was my opinion that
    higher frequencies can be transmitted over coax but not over FR4 because of
    the geometry. Because in a coax there is (almost) no energy loss because the
    TEM wave is "captured" by the outer shield and in a planar setup like
    stripline or microstrip there are E-field and H-field lines vanish into the
    air environment (or somewhere else...). Therefore I'm trying to design a
    coax on a PCB. Am I right with my thoughts, anyway?
  15. John Larkin

    John Larkin Guest

    A couple of things make pcb's lossy: the loss tangent of the material
    (and FR4 is pretty bad) and the copper losses. Copper loss gets bad on
    conventional FR4 boards because

    1. FR4's Er is high, so for a given impedance traces are skinny.

    2. The underside of the copper is treated to bond to the epoxy/glass,
    and the treatment (black oxide or something) greatly increases skin
    losses. Peel some up and look... it's gross.

    3. In the case of microstrip, the current is concentrated on the
    underside (the dirty side) of the trace, so losses are that much
    worse... the shiny topside of the copper is underutilized. Stripline
    would be better, with balanced current density, except that the trace
    will be much thinner, which has its own penalty.

    A good microwave pcb has a low Er, low loss dielectric; is thick, for
    low current density and wide traces; has very smooth copper, which
    means traces and pads peel off easily.

    I don't think any simple geometry tricks (ie, emulating coax) will
    make FR4 any better, and would probably make it worse. For low losses,
    microstrip on a thick board is probably as good as it gets.


  16. Sorry, but that feature is only available on the 0 volt model.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  17. Indeed there are the topologies of the switchers with exactly zero or
    almost zero ripple, assuming the ideal symmetry of everything.

    Vladimir Vassilevsky

    DSP and Mixed Signal Design Consultant
  18. CBFalconer

    CBFalconer Guest

    All it takes is an infinite capacity capacitor. The turn-on time
    and inrush current may be high. However it avoids the need for a
    UPS. Once they get the breakdown voltage up and get them into
    production we can have all the electric cars we want, and dispense
    with all batteries.


    "A man who is right every time is not likely to do very much."
    -- Francis Crick, co-discover of DNA
    "There is nothing more amazing than stupidity in action."
    -- Thomas Matthews
  19. John Larkin

    John Larkin Guest

    Like a polyphase switcher with *big* inductors?

    But I don't want "almost zero ripple", I want the real thing.

  20. Zero ripple is a real thing.
    Imagine the two identical bucks operating 50/50 duty with 180 degree
    phase shift on the common load. Ideally, there will be no ripple at the
    load at all. There are numerous patents on the variations of this idea,
    allowing to adjust the duty, different topologies and such.

    Vladimir Vassilevsky

    DSP and Mixed Signal Design Consultant
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day