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Litz wire Q

Discussion in 'Electronic Design' started by Tim Williams, Mar 24, 2013.

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  1. Tim Williams

    Tim Williams Guest

    30MHz? I hear 3MHz or so is usually where it loses value. There's
    probably something about capacitance between strands, too -- the eddy
    voltage (i.e., the voltage between strands, which would've caused eddy
    currents in a solid conductor) just keeps going up.

    Going up much higher requires extremely fine wire to remain valuable.
    Finest litz I've heard of has strands around #46, which is finer than
    human hair. I don't think they make much finer than that.

  2. Jamie M

    Jamie M Guest

    Hi, shows 2.8MHz max recommended
    for 48AWG litz wire. I guess litz is probably used for a lot higher
    than that, but the Q will go down. For 30MHz the skin depth is
    13.9um! I think 48AWG wire is about 30.48um diameter (0.0012") so you
    would need some higher gauge litz wire maybe if it is made!

  3. Robert Baer

    Robert Baer Guest

    Nominally,what is the highest frequency that litz wire been used at?
    I am guessing 30Mhz is the top end.
  4. Guest

    For local oscillator or front ends tuned by a typical 500 pF variable
    capacitor, the inductance required for the long wave band is about
    2000 uH, for medium wave band bout 200 uH and for some HF band 2 uH.
    Since the inductance is proportional to the square of number of turns,
    so for similar cores, the MW coil requires 10 times the number of
    turns than the HF coil and th LF coil 30 times the number of turns
    than HF. The linear length and hence losses are proportional to the
    number of turns. If you try to squeeze 10-30 times the number of turns
    on a coil former, you have to use thinner wires, increasing losses.

    Thus the Litz wire is critical for LF/MF, but for HF/VHF, the low
    number of turns makes it possible to use a thick conductor, but
    actually only use the surface due to skin effect.
  5. Tim Williams

    Tim Williams Guest

    I think of it this way: although the skin is getting thinner, it goes as
    1/sqrt(F), whereas reactance goes as F. So at higher frequencies, Q is
    simply high enough not to care.

    You can still get some amazing Qs with litz. I've heard of Q over 1000
    for a spider wound type with the finest litz. That's up there with
    polypropylene capacitors, maybe even air variables. I think that was
    LF/MF, don't recall if there are measurements and comparisons at HF+ for

    I don't think this works for transformers though. Transformers are about
    two things, flux density and current density. Even for optimal core
    materials, flux density drops (loss limited instead of saturation
    limited), but it's more like 1/sqrt(F), while flux goes as 1/F. So the
    core gets smaller, and length of turn gets smaller. But copper is still
    copper, and if you can only divide it so far, you're actually going to
    need the same or more!

  6. Robert Baer

    Robert Baer Guest

    None specifically; just a randumb idea that was partly linked to Litz
    Much stronger link to surface smoothness VS frequency - as seen in
    Rogers (and other PCBs).
    Am thinking,all else being kept constant, that a better surface
    smoothness gives a better frequency frequency response/capability.
    A little hard to see why the loss at a given high frequency wold be less.
  7. Robert Baer

    Robert Baer Guest

    Somehow what you wrote cot completely lost, so with apologies i copy
    some of it here to give a more coherent response:
    Burst (gated, instant-on) oscillators are fun.

    The trick is to have every edge, especially the first few, happen just
    on time.
    And to have the prop delay from gate to the first edge be minimal.

    I must commend you,the turn-on is virtually perfect; only the first
    half-cycle is slightly wider.
    This turn-on response is not easy to achieve; i lucked out in trying
    that when i tried an ECL (NOR?) gate where one input was the on/off
    control and the other was for the feedback for oscillation.
    Been over 30 years, but i think that yours is better.
  8. amdx

    amdx Guest

    Some may be interested in this thread on Rap N Tap, a crystal radio
    forum. Claim is high Q in the AMBCB using three pieces of 640/46 litz.**+Advanced+Forum&M=False&S=True

    Or, watch the wrap,**+Advanced+Forum&M=False&S=True
  9. Robert Baer

    Robert Baer Guest

  10. amdx

    amdx Guest

    When I pasted the link it showed as 4 lines of text,
    so I pasted it as a quotation and it was one line.
    Obviously it fixed itself when I mailed it.

    But what about the coil with a Q of 2000?
  11. Jamie

    Jamie Guest

    That's just in case you were not watching for the wrap when you looked
    it the first time! :)(

    Actually, we've tested litz wire before, because we use it in a 100khz
    application for a transformer coupling a voltage multiplier in a SF6
    filled vessel. If memory serves, I think 5Mhz was the tops before it
    got hairy.. But then again, there are different constructions of this

    You got spiral twist, braided and straight bunch with a thread wrap
    to hold it together, we use the bunched style.

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