Bifilar Wound Balun Transformer

Discussion in 'Electronic Design' started by rickman, Nov 3, 2012.

  1. rickman

    rickman Guest

    I am learning a bit about antenna design and one of the references I
    found talks about coupling the antenna to the feedline with a bifilar
    wound balun transformer. I dug a bit and although I found any number
    of references talking about bifilar wound baluns, none explained clearly
    why it is important to be bifilar wound.

    Any pointers?

    Rick
    rickman, Nov 3, 2012
    #1
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  2. rickman

    rickman Guest

    On 11/3/2012 5:15 PM, rickman wrote:
    > I am learning a bit about antenna design and one of the references I
    > found talks about coupling the antenna to the feedline with a bifilar
    > wound balun transformer. I dug a bit and although I found any number of
    > references talking about bifilar wound baluns, none explained clearly
    > why it is important to be bifilar wound.
    >
    > Any pointers?
    >
    > Rick


    Ah, a picture is worth a thousand words. I finally found a page that
    shows a bifilar balun in the application circuit I would be using it
    with and it makes perfect sense now. Well, mostly. The circuit is
    single ended to differential coupling.

    I get why the thing is wired up the way it is, I suppose it is important
    to use a bifilar winding to keep the two windings as identical as possible.

    Actually, I've looked at too many pages. I had two pages mixed up. I
    see the one that showed a toroidal core matching transformer is not the
    same page as the one that said to bifilar wind the balun. Seems the
    first one is a transformer like I'm used to seeing, but the bifilar
    wound balun is used in a different way that can't match impedance over
    the range I believe the toroid is doing.

    It's pretty amazing how many web pages there are that cover in such
    detail so many highly specialized topics! And most of these are hobby
    pages!!!

    Rick
    rickman, Nov 3, 2012
    #2
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  3. rickman

    Bill Sloman Guest

    On Nov 4, 8:15 am, rickman <> wrote:
    > I am learning a bit about antenna design and one of the references I
    > found talks about coupling the antenna to the feedline with a bifilar
    > wound balun  transformer.  I dug a bit and although I found any number
    > of references talking about bifilar wound baluns, none explained clearly
    > why it is important to be bifilar wound.
    >
    > Any pointers?


    A balun is actually a transmission line transformer.

    http://en.wikipedia.org/wiki/Balun

    The twisted pair that constitutes the bifilar winding is a
    transmission line, with a particular characteristic impedance which
    depends on the diameter of the wire involved and the thickness and
    natire of its insulation.

    IIRR a twisted pair twisted out of enamel-insulated transformer wire
    has characteristic impedance in the ball-park of 120R.

    Google throws up a few tutorial papers

    http://home.earthlink.net/~christrask/TraskTLTTutorial.pdf

    http://www.highfrequencyelectronics.com/Archives/Jan06/HFE0106_TraskPart2.pdf

    Transmission line transformers keep on working to much higher
    frequencies than conventional transformers - the inter-winding
    capacitance becomes part of the transmission line rather than a simple
    parasitic load - and in fact only start falling over when the
    wavelength of the frequency being transmitted approaches the length of
    the winding.

    And - for John Larkin's benefit - this is electronics.

    --
    Bill Sloman, Sydney
    Bill Sloman, Nov 3, 2012
    #3
  4. rickman

    Phil Allison Guest

    "Bill Sloman"

    > Any pointers?


    A balun is actually a transmission line transformer.

    http://en.wikipedia.org/wiki/Balun

    The twisted pair that constitutes the bifilar winding is a
    transmission line, with a particular characteristic impedance which
    depends on the diameter of the wire involved and the thickness and
    natire of its insulation.

    IIRR a twisted pair twisted out of enamel-insulated transformer wire
    has characteristic impedance in the ball-park of 120R.


    ** For clarity, it needs to be said that twisting of a pair of parallel
    wires in incidental to their operation as a transmission line. Twisting
    merely serves to eliminate radiation and pick up of external EM fields.

    A "bifilar wound " transformer may well have no twisting of the wires at
    all, but simply has them laid side by side in smooth layers.


    .... Phil
    Phil Allison, Nov 3, 2012
    #4
  5. rickman

    Tim Williams Guest

    "Bill Sloman" <> wrote in message
    news:...
    > A balun is actually a transmission line transformer.


    Not a necessary construction method; a balun is just a transformer with
    tapping such that it inverts one side.

    > The twisted pair that constitutes the bifilar winding is a
    > transmission line, with a particular characteristic impedance which
    > depends on the diameter of the wire involved and the thickness and
    > natire of its insulation.
    >
    > IIRR a twisted pair twisted out of enamel-insulated transformer wire
    > has characteristic impedance in the ball-park of 120R.


    I got closer to 30 ohms last I measured a pair. Enamel is a whole lot
    thinner than extruded jacketing. It's going to be even lower in a
    piled-up winding due to the crowding.

    The low frequency way to think of it: your leakage inductance is almost
    exactly the inductance of the windings as a transmission line.

    If you take a piece of twisted pair 1m long, it'll have maybe 0.5uH
    inductance (measured at one end of the pair, shorting the far end, at a
    frequency well below the electrical length of the line). If you wind it
    up onto a form with an air core (making a bifilar solenoid, say), the
    self-inductance of each winding might be a few uH, while the inductance
    between wires remains the same (it's lower, if anything). Note that you
    can measure this leakage two ways: terminus shorted (as a transmission
    line) or secondary shorted (transformer leakage). The difference is, you
    test P1-S1 and short P2-S2, or test P1-P2 and short S1-S2.

    Now if you insert a permeable core, inductance goes way up (into the mH,
    perhaps), and coupling coefficient likewise goes up (some fraction less
    than 1.0). But leakage remains fairly constant.

    Leakage depends almost entirely on winding construction. Self-inductance
    depends on the windings and core. Coupling coefficient is the factor
    relating the two.

    (Yes, you can make a transformer that specifically depends on core
    geometry, not just winding construction. An example would be two coils at
    right angles, with a core snaked through each. Without the core, they
    have zero mutual inductance (infinite leakage). With the core, it's
    nonzero. I'm more interested in applications where you actually give a
    damn about performance in the first place. :) )

    The important thing about transmission line transformers is to forget
    about using them as transformers. Use them as transmission lines! If you
    put a few loops of coax on a core and drive the shield (calling the shield
    the primary, P1-P2), you can't expect any useful kind of behavior from
    that, because the shield carries all sorts of crazy currents, depending on
    how it's looped through, and which turns it's adjacent to, etc. If
    instead you drive the transmission line from one end (P1-S1), you'll get
    the same signal out (P2-S2), delayed, except the core allows you
    common-mode voltage. You could flip the terminal end around (S2-P2), and
    get an inverted signal!
    http://www.picosecond.com/product/product.asp?prod_id=47
    That's more or less what they do here. The shield necessarily does still
    carry a signal (the act of flipping the terminals forces the output
    voltage onto the shield anyway), but this occurs "after" the signal
    propagated through, and what you do with the shield is now an open
    variable -- you could loop it through a whole bunch of ferrite beads,
    damping out any oscillations.

    It follows that you can create any ratio by connecting transmission lines
    in parallel, looping them through a core (it doesn't even matter that the
    same core is used, it's just a common mode choke now!), and connecting any
    desired series-parallel combination on input and output sides to set the
    desired impedance and ratio.

    The dirty secret of transmission line transformers is, they aren't at all
    interested in reducing leakage inductance, or capacitance, or anything
    like that. It's just a big common-mode choke that lets you pipe signals
    from wherever to wherever else.

    Tim

    --
    Deep Friar: a very philosophical monk.
    Website: http://webpages.charter.net/dawill/tmoranwms
    Tim Williams, Nov 3, 2012
    #5
  6. rickman

    Bill Sloman Guest

    On Nov 4, 10:50 am, "Tim Williams" <> wrote:
    > "Bill Sloman" <> wrote in message
    >
    > news:...
    >
    > > A balun is actually a transmission line transformer.

    >
    > Not a necessary construction method; a balun is just a transformer with
    > tapping such that it inverts one side.


    In the sense that the original source of the name was as a contraction
    of "balanced to unbalanced transformer".

    The wikipea article makes it fairly clear that one should understand
    it as a transmission line transformer. As Phil Alison correctly points
    out, you don't actually have to twist the wires together to make them
    into a transmission line, though twisting them is a mechanism which
    does keep the pair close together.

    > > The twisted pair that constitutes the bifilar winding is a
    > > transmission line, with a particular characteristic impedance which
    > > depends on the diameter of the wire involved and the thickness and
    > > natire of its insulation.

    >
    > > IIRR a twisted pair twisted out of enamel-insulated transformer wire
    > > has characteristic impedance in the ball-park of 120R.

    >
    > I got closer to 30 ohms last I measured a pair.


    How thick was the wire? The thickness of the enamel is more or less
    independent of the copper gauge, and the impedances is going to be
    appreciablyb higher for 40# gauge wire than for 10# gauge.

    > Enamel is a whole lot thinner than extruded jacketing.  It's going tobe even lower in a
    > piled-up winding due to the crowding.


    Most of the field is confined between the two wires of the pair. I
    wouldn't think that adjacent wires would make much difference.

    > The low frequency way to think of it: your leakage inductance is almost
    > exactly the inductance of the windings as a transmission line.
    >
    > If you take a piece of twisted pair 1m long, it'll have maybe 0.5uH
    > inductance (measured at one end of the pair, shorting the far end, at a
    > frequency well below the electrical length of the line).  If you wind it
    > up onto a form with an air core (making a bifilar solenoid, say), the
    > self-inductance of each winding might be a few uH, while the inductance
    > between wires remains the same (it's lower, if anything).  Note that you
    > can measure this leakage two ways: terminus shorted (as a transmission
    > line) or secondary shorted (transformer leakage).  The difference is, you
    > test P1-S1 and short P2-S2, or test P1-P2 and short S1-S2.
    >
    > Now if you insert a permeable core, inductance goes way up (into the mH,
    > perhaps), and coupling coefficient likewise goes up (some fraction less
    > than 1.0).  But leakage remains fairly constant.
    >
    > Leakage depends almost entirely on winding construction.  Self-inductance
    > depends on the windings and core.  Coupling coefficient is the factor
    > relating the two.
    >
    > (Yes, you can make a transformer that specifically depends on core
    > geometry, not just winding construction.  An example would be two coilsat
    > right angles, with a core snaked through each.  Without the core, they
    > have zero mutual inductance (infinite leakage).  With the core, it's
    > nonzero.  I'm more interested in applications where you actually give a
    > damn about performance in the first place. :) )
    >
    > The important thing about transmission line transformers is to forget
    > about using them as transformers.


    <snip>

    This is wrong. I've certainly used them as 1:1 isolating transformers
    and they worked fine.

    > It follows that you can create any ratio by connecting transmission lines
    > in parallel, looping them through a core (it doesn't even matter that the
    > same core is used, it's just a common mode choke now!), and connecting any
    > desired series-parallel combination on input and output sides to set the
    > desired impedance and ratio.


    There is some interesting literature on creating integer ratio
    transmission line transformers, and if you are clever enough I'm
    fairly sure that you can create non-integer ratios - I think there's a
    famous paper on the subject. There are also a lot of ways of getting
    it wrong.

    > The dirty secret of transmission line transformers is, they aren't at all
    > interested in reducing leakage inductance, or capacitance, or anything
    > like that.  It's just a big common-mode choke that lets you pipe signals
    > from wherever to wherever else.


    That's certainly one way of using them.

    --
    Bill Sloman, Sydney
    Bill Sloman, Nov 4, 2012
    #6
  7. rickman

    Tim Williams Guest

    "John Larkin" <> wrote in
    message news:...
    > We do exactly that in a bunch of products, namely use the shield as a
    > primary winding and the inner as the fully isolated secondary of a
    > transformer. We do 1:1 and 1:2 (voltage step up) at levels from 5
    > volts to over 100.
    >
    > https://dl.dropbox.com/u/53724080/Circuits/Xfmrs.JPG
    >
    > This makes a transformer with very low leakage inductance, so we get
    > sub-ns rise times into a 50 ohm load.


    Except that, as I said, the leakage is not particularly low. One gets
    better performance in that regard from, say, copper foil pairs (which,
    ultimately, is still doing the same thing, but with a low impedance
    symmetrical stripline, not 50 ohm coax). Which is often done in power
    circuitry. But "very low leakage" is not what you're going for, so it's
    best not to claim that's what you're doing.

    Tim

    --
    Deep Friar: a very philosophical monk.
    Website: http://webpages.charter.net/dawill/tmoranwms
    Tim Williams, Nov 4, 2012
    #7
  8. rickman

    rickman Guest

    On 11/3/2012 9:28 PM, Jeff Liebermann wrote:
    > On Sat, 03 Nov 2012 17:15:27 -0400, rickman<> wrote:
    >
    >> Any pointers?
    >> Rick

    >
    > If you're connecting to an antenna, this might be helpful:
    >
    > A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing
    > <http://audiosystemsgroup.com/RFI-Ham.pdf>
    > Quoting:
    > The primary function of most baluns, at least in our ham
    > stations, is to minimize the interaction of our antennas
    > with the transmission lines that connect them to our radios.
    > There's more to baluns than just impedance matching.
    >


    Wow, that's a lot of reading. Thanks.

    Rick
    rickman, Nov 4, 2012
    #8
  9. rickman

    rickman Guest

    On 11/3/2012 9:42 PM, John Larkin wrote:
    > On Sat, 3 Nov 2012 20:40:37 -0500, "Tim Williams"
    > <> wrote:
    >
    >> "John Larkin"<> wrote in
    >> message news:...
    >>> We do exactly that in a bunch of products, namely use the shield as a
    >>> primary winding and the inner as the fully isolated secondary of a
    >>> transformer. We do 1:1 and 1:2 (voltage step up) at levels from 5
    >>> volts to over 100.
    >>>
    >>> https://dl.dropbox.com/u/53724080/Circuits/Xfmrs.JPG
    >>>
    >>> This makes a transformer with very low leakage inductance, so we get
    >>> sub-ns rise times into a 50 ohm load.

    >>
    >> Except that, as I said, the leakage is not particularly low. One gets
    >> better performance in that regard from, say, copper foil pairs (which,
    >> ultimately, is still doing the same thing, but with a low impedance
    >> symmetrical stripline, not 50 ohm coax). Which is often done in power
    >> circuitry. But "very low leakage" is not what you're going for, so it's
    >> best not to claim that's what you're doing.
    >>
    >> Tim

    >
    > But it works.


    See, this is the sort of stuff that, if I were a potential customer,
    would turn me off to doing business with you. Geeze, if I am talking to
    someone about what is going on in a system and they say to me, "but it
    works", I would think they didn't understand it at all.

    Do you not see how your posts make you look?

    Rick
    rickman, Nov 4, 2012
    #9
  10. rickman

    Fred Abse Guest

    On Sat, 03 Nov 2012 18:50:54 -0500, Tim Williams wrote:

    > The important thing about transmission line transformers is to forget
    > about using them as transformers. Use them as transmission lines!


    Anybody know how to accurately model a transmission line transformer in
    Spice, taking into account core properties?

    --
    "For a successful technology, reality must take precedence
    over public relations, for nature cannot be fooled."
    (Richard Feynman)
    Fred Abse, Nov 4, 2012
    #10
  11. rickman

    Fred Bartoli Guest

    Fred Abse a écrit :
    > On Sat, 03 Nov 2012 18:50:54 -0500, Tim Williams wrote:
    >
    >> The important thing about transmission line transformers is to forget
    >> about using them as transformers. Use them as transmission lines!

    >
    > Anybody know how to accurately model a transmission line transformer in
    > Spice, taking into account core properties?
    >


    For a simple one, just as it is:
    use a TLine/RLC tline and between the 2 ""shield/ref plane" connections
    you just tie the magnetizing inductance, with maybe your core model
    (losses, non linearities, hysteresis,...)


    --
    Thanks,
    Fred.
    Fred Bartoli, Nov 4, 2012
    #11
  12. rickman

    Fred Bartoli Guest

    John Larkin a écrit :
    > On Sun, 04 Nov 2012 18:57:27 +0100, Fred Bartoli <" "> wrote:
    >
    >> Fred Abse a écrit :
    >>> On Sat, 03 Nov 2012 18:50:54 -0500, Tim Williams wrote:
    >>>
    >>>> The important thing about transmission line transformers is to forget
    >>>> about using them as transformers. Use them as transmission lines!
    >>> Anybody know how to accurately model a transmission line transformer in
    >>> Spice, taking into account core properties?
    >>>

    >> For a simple one, just as it is:
    >> use a TLine/RLC tline and between the 2 ""shield/ref plane" connections
    >> you just tie the magnetizing inductance, with maybe your core model
    >> (losses, non linearities, hysteresis,...)

    >
    > What's interesting about the LT Spice transmission lines is that they
    > have no common-mode DC continuity between ends. They act as if there
    > is an ideal 1:1 isolation transformer in the circuit.
    >
    > That sort of makes sense, since, say, the outer conductor of a coax
    > has its own complex impedance against the universe, and Spice elects
    > to not model that. Still, it can throw you if you don't know about it,
    > and make baluns seem to work much better than they will in real life.
    >


    If you want to accurately model a coax cable you need two TLines. One
    modeling the center/shield transmission line, and a second one to model
    the shield WRT to "space".

    > So a txline can make a handy 1:1 ideal transformer. Unlike a 1:1 VCVS,
    > it's bidirectional and the output loads the input.
    >


    The "standard" perfect transformer is composed of a vcvs to transport
    voltage to the secondary and a CCCS to reflect the secondary current
    back to the primary, and a 0 voltage source to probe it.
    It is much less computationally demanding than the Tline which has to
    maintain history.


    --
    Thanks,
    Fred.
    Fred Bartoli, Nov 4, 2012
    #12
  13. rickman

    John S Guest

    On 11/3/2012 10:25 PM, rickman wrote:
    > On 11/3/2012 9:42 PM, John Larkin wrote:
    >> On Sat, 3 Nov 2012 20:40:37 -0500, "Tim Williams"
    >> <> wrote:
    >>
    >>> "John Larkin"<> wrote in
    >>> message news:...
    >>>> We do exactly that in a bunch of products, namely use the shield as a
    >>>> primary winding and the inner as the fully isolated secondary of a
    >>>> transformer. We do 1:1 and 1:2 (voltage step up) at levels from 5
    >>>> volts to over 100.
    >>>>
    >>>> https://dl.dropbox.com/u/53724080/Circuits/Xfmrs.JPG
    >>>>
    >>>> This makes a transformer with very low leakage inductance, so we get
    >>>> sub-ns rise times into a 50 ohm load.
    >>>
    >>> Except that, as I said, the leakage is not particularly low. One gets
    >>> better performance in that regard from, say, copper foil pairs (which,
    >>> ultimately, is still doing the same thing, but with a low impedance
    >>> symmetrical stripline, not 50 ohm coax). Which is often done in power
    >>> circuitry. But "very low leakage" is not what you're going for, so it's
    >>> best not to claim that's what you're doing.
    >>>
    >>> Tim

    >>
    >> But it works.

    >
    > See, this is the sort of stuff that, if I were a potential customer,


    Well, apparently you're not.

    > would turn me off to doing business with you.


    Oops! One potential customer lost! Damn, John, this will put you out of
    business.


    Geeze, if I am talking to
    > someone about what is going on in a system and they say to me, "but it
    > works", I would think they didn't understand it at all.


    Maybe the foot is on the other shoe. Maybe you didn't understand it at all.

    > Do you not see how your posts make you look?
    >
    > Rick


    And you understand how your posts look? That's curious.
    John S, Nov 4, 2012
    #13
  14. rickman

    Jamie Guest

    John S wrote:
    > On 11/3/2012 10:25 PM, rickman wrote:
    >
    >> On 11/3/2012 9:42 PM, John Larkin wrote:
    >>
    >>> On Sat, 3 Nov 2012 20:40:37 -0500, "Tim Williams"
    >>> <> wrote:
    >>>
    >>>> "John Larkin"<> wrote in
    >>>> message news:...
    >>>>
    >>>>> We do exactly that in a bunch of products, namely use the shield as a
    >>>>> primary winding and the inner as the fully isolated secondary of a
    >>>>> transformer. We do 1:1 and 1:2 (voltage step up) at levels from 5
    >>>>> volts to over 100.
    >>>>>
    >>>>> https://dl.dropbox.com/u/53724080/Circuits/Xfmrs.JPG
    >>>>>
    >>>>> This makes a transformer with very low leakage inductance, so we get
    >>>>> sub-ns rise times into a 50 ohm load.
    >>>>
    >>>>
    >>>> Except that, as I said, the leakage is not particularly low. One gets
    >>>> better performance in that regard from, say, copper foil pairs (which,
    >>>> ultimately, is still doing the same thing, but with a low impedance
    >>>> symmetrical stripline, not 50 ohm coax). Which is often done in power
    >>>> circuitry. But "very low leakage" is not what you're going for, so
    >>>> it's
    >>>> best not to claim that's what you're doing.
    >>>>
    >>>> Tim
    >>>
    >>>
    >>> But it works.

    >>
    >>
    >> See, this is the sort of stuff that, if I were a potential customer,

    >
    >
    > Well, apparently you're not.
    >
    >> would turn me off to doing business with you.

    >
    >
    > Oops! One potential customer lost! Damn, John, this will put you out of
    > business.
    >
    >
    > Geeze, if I am talking to
    >
    >> someone about what is going on in a system and they say to me, "but it
    >> works", I would think they didn't understand it at all.

    >
    >
    > Maybe the foot is on the other shoe. Maybe you didn't understand it at all.
    >
    >> Do you not see how your posts make you look?
    >>
    >> Rick

    >
    >
    > And you understand how your posts look? That's curious.
    >
    >

    Those that don't know shit, should shit elsewhere ! Get it?

    The doctor made a mistake when you were born, they disposed the best
    part that came out of your mother, the afterbirth.

    Jamie
    Jamie, Nov 4, 2012
    #14
  15. rickman

    rickman Guest

    On 11/4/2012 3:49 PM, John Larkin wrote:
    > On Sat, 03 Nov 2012 23:25:46 -0400, rickman<> wrote:
    >
    >> On 11/3/2012 9:42 PM, John Larkin wrote:
    >>> On Sat, 3 Nov 2012 20:40:37 -0500, "Tim Williams"
    >>> <> wrote:
    >>>
    >>>> "John Larkin"<> wrote in
    >>>> message news:...
    >>>>> We do exactly that in a bunch of products, namely use the shield as a
    >>>>> primary winding and the inner as the fully isolated secondary of a
    >>>>> transformer. We do 1:1 and 1:2 (voltage step up) at levels from 5
    >>>>> volts to over 100.
    >>>>>
    >>>>> https://dl.dropbox.com/u/53724080/Circuits/Xfmrs.JPG
    >>>>>
    >>>>> This makes a transformer with very low leakage inductance, so we get
    >>>>> sub-ns rise times into a 50 ohm load.
    >>>>
    >>>> Except that, as I said, the leakage is not particularly low. One gets
    >>>> better performance in that regard from, say, copper foil pairs (which,
    >>>> ultimately, is still doing the same thing, but with a low impedance
    >>>> symmetrical stripline, not 50 ohm coax). Which is often done in power
    >>>> circuitry. But "very low leakage" is not what you're going for, so it's
    >>>> best not to claim that's what you're doing.
    >>>>
    >>>> Tim
    >>>
    >>> But it works.

    >>
    >> See, this is the sort of stuff that, if I were a potential customer,
    >> would turn me off to doing business with you. Geeze, if I am talking to
    >> someone about what is going on in a system and they say to me, "but it
    >> works", I would think they didn't understand it at all.

    >
    > I'm an engineer. I don't need to understand it, I only need to make it
    > work.


    Amazing. There are times when a line is drawn and a designer says, "I
    understand this well enough", but the way you say it comes off like an
    amateur. I have spent a lot of time in my career fixing systems
    designed by people who obviously "only needed to make it work", but then
    it stopped working for some unknown reason.


    > If a deep theoretical understanding of transmission-line
    > transformers is helpful, I might use it. But if an hour of
    > instinct-driven experimenting works, I'll go with that. My
    > mosfet-transmission-line output stage, which we've used thousands of
    > times, took about an hour of experimenting to design.
    >
    > Some of the stuff that we do is so complex that closed-form solutions
    > are impossible, and serious simulation would cost way too much time
    > and money.
    >
    > In the electronic design business, we seldom really understand what
    > we're doing, at the first-principles level.


    That is scary. I find a lot of people like that though. I just thought
    they were posers. I've never heard any of them brag about it.


    > We usually work further up
    > the abstraction stack. We usually buy parts, read data sheets, and
    > connect them up. It's actually unusual to *make* a part. [1]


    Yeah, that's what everyone does, but when they connect those parts,
    typically they understand everything about them and how to connect them
    that they need to.


    >> Do you not see how your posts make you look?

    >
    > I posted pics of actual isolating transformers made with micro-coax.
    > And some nice sub-ns-risetime 100 volt pulses that were pumped through
    > similar transformers. Why would a customer be turned off by something
    > that works?
    >
    > A sub-ns rise time into a 50 ohm load implies equivalent leakage
    > inductance in the 10s of nH.


    I'm talking about the statements you make that sound like they are from
    someone with no level of understanding.

    I shouldn't be posting about this. It is clear that you understand
    completely what you are saying and I expect you understand how it makes
    you appear. So sorry for bothering you with this.

    Rick
    rickman, Nov 4, 2012
    #15
  16. rickman

    Jamie Guest

    John Larkin wrote:

    > On Sat, 03 Nov 2012 23:25:46 -0400, rickman <> wrote:
    >
    >
    >>On 11/3/2012 9:42 PM, John Larkin wrote:
    >>
    >>>On Sat, 3 Nov 2012 20:40:37 -0500, "Tim Williams"
    >>><> wrote:
    >>>
    >>>
    >>>>"John Larkin"<> wrote in
    >>>>message news:...
    >>>>
    >>>>>We do exactly that in a bunch of products, namely use the shield as a
    >>>>>primary winding and the inner as the fully isolated secondary of a
    >>>>>transformer. We do 1:1 and 1:2 (voltage step up) at levels from 5
    >>>>>volts to over 100.
    >>>>>
    >>>>>https://dl.dropbox.com/u/53724080/Circuits/Xfmrs.JPG
    >>>>>
    >>>>>This makes a transformer with very low leakage inductance, so we get
    >>>>>sub-ns rise times into a 50 ohm load.
    >>>>
    >>>>Except that, as I said, the leakage is not particularly low. One gets
    >>>>better performance in that regard from, say, copper foil pairs (which,
    >>>>ultimately, is still doing the same thing, but with a low impedance
    >>>>symmetrical stripline, not 50 ohm coax). Which is often done in power
    >>>>circuitry. But "very low leakage" is not what you're going for, so it's
    >>>>best not to claim that's what you're doing.
    >>>>
    >>>>Tim
    >>>
    >>>But it works.

    >>
    >>See, this is the sort of stuff that, if I were a potential customer,
    >>would turn me off to doing business with you. Geeze, if I am talking to
    >>someone about what is going on in a system and they say to me, "but it
    >>works", I would think they didn't understand it at all.

    >
    >
    > I'm an engineer. I don't need to understand it, I only need to make it
    > work. If a deep theoretical understanding of transmission-line
    > transformers is helpful, I might use it. But if an hour of
    > instinct-driven experimenting works, I'll go with that. My
    > mosfet-transmission-line output stage, which we've used thousands of
    > times, took about an hour of experimenting to design.
    >
    > Some of the stuff that we do is so complex that closed-form solutions
    > are impossible, and serious simulation would cost way too much time
    > and money.
    >
    > In the electronic design business, we seldom really understand what
    > we're doing, at the first-principles level. We usually work further up
    > the abstraction stack. We usually buy parts, read data sheets, and
    > connect them up. It's actually unusual to *make* a part. [1]
    >
    >
    >>Do you not see how your posts make you look?

    >
    >
    > I posted pics of actual isolating transformers made with micro-coax.
    > And some nice sub-ns-risetime 100 volt pulses that were pumped through
    > similar transformers. Why would a customer be turned off by something
    > that works?
    >
    > A sub-ns rise time into a 50 ohm load implies equivalent leakage
    > inductance in the 10s of nH.
    >
    > [1] invite interesting tales of actually making components.
    >
    >

    At least you actually do something, not like a good many here that
    would like to make people think otherwise.

    I spend more time at actually experimenting with what works the best
    instead of fighting with PC software that only gets it close but not
    good enough.

    I just love those that talk shit and most likely hardly even touch a
    piece of equipment. When they do I am sure they're all thumbs and
    fingers with it and most likely end up getting some one else to do it
    for them and take all the credit for it.

    Those guilty of this need not to step forward, I already know who
    most of you are.

    Jamie
    Jamie, Nov 4, 2012
    #16
  17. On Sun, 04 Nov 2012 16:37:19 -0500, the renowned Jamie
    <> wrote:

    >John Larkin wrote:
    >
    >> On Sat, 03 Nov 2012 23:25:46 -0400, rickman <> wrote:
    >>
    >>
    >>>On 11/3/2012 9:42 PM, John Larkin wrote:
    >>>
    >>>>On Sat, 3 Nov 2012 20:40:37 -0500, "Tim Williams"
    >>>><> wrote:
    >>>>
    >>>>
    >>>>>"John Larkin"<> wrote in
    >>>>>message news:...
    >>>>>
    >>>>>>We do exactly that in a bunch of products, namely use the shield as a
    >>>>>>primary winding and the inner as the fully isolated secondary of a
    >>>>>>transformer. We do 1:1 and 1:2 (voltage step up) at levels from 5
    >>>>>>volts to over 100.
    >>>>>>
    >>>>>>https://dl.dropbox.com/u/53724080/Circuits/Xfmrs.JPG
    >>>>>>
    >>>>>>This makes a transformer with very low leakage inductance, so we get
    >>>>>>sub-ns rise times into a 50 ohm load.
    >>>>>
    >>>>>Except that, as I said, the leakage is not particularly low. One gets
    >>>>>better performance in that regard from, say, copper foil pairs (which,
    >>>>>ultimately, is still doing the same thing, but with a low impedance
    >>>>>symmetrical stripline, not 50 ohm coax). Which is often done in power
    >>>>>circuitry. But "very low leakage" is not what you're going for, so it's
    >>>>>best not to claim that's what you're doing.
    >>>>>
    >>>>>Tim
    >>>>
    >>>>But it works.
    >>>
    >>>See, this is the sort of stuff that, if I were a potential customer,
    >>>would turn me off to doing business with you. Geeze, if I am talking to
    >>>someone about what is going on in a system and they say to me, "but it
    >>>works", I would think they didn't understand it at all.

    >>
    >>
    >> I'm an engineer. I don't need to understand it, I only need to make it
    >> work. If a deep theoretical understanding of transmission-line
    >> transformers is helpful, I might use it. But if an hour of
    >> instinct-driven experimenting works, I'll go with that. My
    >> mosfet-transmission-line output stage, which we've used thousands of
    >> times, took about an hour of experimenting to design.
    >>
    >> Some of the stuff that we do is so complex that closed-form solutions
    >> are impossible, and serious simulation would cost way too much time
    >> and money.
    >>
    >> In the electronic design business, we seldom really understand what
    >> we're doing, at the first-principles level. We usually work further up
    >> the abstraction stack. We usually buy parts, read data sheets, and
    >> connect them up. It's actually unusual to *make* a part. [1]
    >>
    >>
    >>>Do you not see how your posts make you look?

    >>
    >>
    >> I posted pics of actual isolating transformers made with micro-coax.
    >> And some nice sub-ns-risetime 100 volt pulses that were pumped through
    >> similar transformers. Why would a customer be turned off by something
    >> that works?
    >>
    >> A sub-ns rise time into a 50 ohm load implies equivalent leakage
    >> inductance in the 10s of nH.
    >>
    >> [1] invite interesting tales of actually making components.
    >>
    >>

    > At least you actually do something, not like a good many here that
    >would like to make people think otherwise.
    >
    > I spend more time at actually experimenting with what works the best
    >instead of fighting with PC software that only gets it close but not
    >good enough.
    >
    > I just love those that talk shit and most likely hardly even touch a
    >piece of equipment. When they do I am sure they're all thumbs and
    >fingers with it and most likely end up getting some one else to do it
    >for them and take all the credit for it.


    I had a guy tell me a cheap scope (he always buys the most expensive
    equipment) I got for him was broken-- turns out the brightness control
    (or whatever you call it on a digital scope) was turned down. Same guy
    claimed an expensive SRS bridge with 0.1% accuracy was giving 10%
    error on a reading-- turned out he was using 100Hz to measure a
    tens-of-pF cap and it was performing well within spec according to the
    manual. He has written peer-reviewed papers on these things.. sad.
    >
    > Those guilty of this need not to step forward, I already know who
    >most of you are.
    >
    >Jamie


    It's a rare person that can get all the theory right and the practice
    right- they deserve to be well-rewarded.


    Best regards,
    Spehro Pefhany
    --
    "it's the network..." "The Journey is the reward"
    Info for manufacturers: http://www.trexon.com
    Embedded software/hardware/analog Info for designers: http://www.speff.com
    Spehro Pefhany, Nov 4, 2012
    #17
  18. rickman

    Tim Williams Guest

    "John Larkin" <> wrote in
    message news:...
    > How deep does your understanding go? Quantum mechanics?


    As a physicist, I can affirm that. Others may vary.

    > String theory?


    Doesn't count -- even the string theorists don't understand the stuff. ;-)

    > Do you do closed-form Maxwell's Equations on every circuit? Or full EM
    > simulation?


    And you don't?

    I do on every single board I make. Not closed-form, but open-form
    approximation, qualitative accuracy. Implemented in wetware, too. Works
    very well.

    > I'm not bragging. I wish I had the tools to fully understand or
    > simulate everything we do, down to the physics. Sometimes you do
    > whatever works.


    Well, if you really wished, you'd buy the entire Ansoft suite and *do*
    it -- but I'm guessing that wish isn't as unconditional as it was phrased.
    In actuality, you don't care at all, and are more than happy enough
    guessing. Which again illustrates your inconsistent self-representation.

    <snip>
    <quoted from proceeding post>
    > I posted pics of actual isolating transformers made with micro-coax.
    > And some nice sub-ns-risetime 100 volt pulses that were pumped through
    > similar transformers. Why would a customer be turned off by something
    >that works?
    >
    > A sub-ns rise time into a 50 ohm load implies equivalent leakage
    > inductance in the 10s of nH.


    Are you aware that ~20nH is ~86mm of 50 ohm, 0.67c coax?

    Assuming the headers pictured are 0.1" centers, the cores are roughly T37
    size ferrites, a bit thicker than usual. I get 14mm for the length of a
    single turn on a regular T37, so it might be closer to 18mm per turn,
    maybe 20mm with coax thickness. That's 60mm total length, or 14nH. The
    soldered connections and board traces have almost as much, depending on if
    there's a ground plane just out of sight or not. But by then it's not
    mutual, which is all the more reason it's not LL you're supposing about.

    Actual performance will show helical resonator action starting around
    1GHz, which is what the under-hump on your leading edge comes from. And
    probably other nasties if you tested it with a ps generator rather than
    the "sub-ns" this particular device produces.

    Tim

    --
    Deep Friar: a very philosophical monk.
    Website: http://webpages.charter.net/dawill/tmoranwms
    Tim Williams, Nov 5, 2012
    #18
  19. rickman

    rickman Guest

    On 11/4/2012 8:43 PM, Tim Williams wrote:
    > "John Larkin"<> wrote in
    > message news:...
    >> How deep does your understanding go? Quantum mechanics?

    >
    > As a physicist, I can affirm that. Others may vary.


    I learned a little in chemistry classes... very little.


    >> String theory?

    >
    > Doesn't count -- even the string theorists don't understand the stuff. ;-)


    My understanding is not that they don't understand it, it just doesn't
    predict anything different from existing quantum theory.


    >> Do you do closed-form Maxwell's Equations on every circuit? Or full EM
    >> simulation?

    >
    > And you don't?
    >
    > I do on every single board I make. Not closed-form, but open-form
    > approximation, qualitative accuracy. Implemented in wetware, too. Works
    > very well.


    Have you solved the Schrödinger wave equation for any of your systems.
    Only then will I call you a real engineer ;)


    > Are you aware that ~20nH is ~86mm of 50 ohm, 0.67c coax?
    >
    > Assuming the headers pictured are 0.1" centers, the cores are roughly T37
    > size ferrites, a bit thicker than usual. I get 14mm for the length of a
    > single turn on a regular T37, so it might be closer to 18mm per turn,
    > maybe 20mm with coax thickness. That's 60mm total length, or 14nH. The
    > soldered connections and board traces have almost as much, depending on if
    > there's a ground plane just out of sight or not. But by then it's not
    > mutual, which is all the more reason it's not LL you're supposing about.
    >
    > Actual performance will show helical resonator action starting around
    > 1GHz, which is what the under-hump on your leading edge comes from. And
    > probably other nasties if you tested it with a ps generator rather than
    > the "sub-ns" this particular device produces.


    Hey, want to help me design a LF shielded loop antenna from coax? It
    sounds like it would be right down your alley! I don't know nothing
    about birthin' no babies, Ms. Scarlett! But it looks like I'm going to
    have to learn...

    Rick
    rickman, Nov 5, 2012
    #19
  20. rickman

    Tim Williams Guest

    "rickman" <> wrote in message
    news:k777h0$knd$...
    >>> String theory?

    >>
    >> Doesn't count -- even the string theorists don't understand the stuff.
    >> ;-)

    >
    > My understanding is not that they don't understand it, it just doesn't
    > predict anything different from existing quantum theory.


    Notwithstanding Feynman's quote, "nobody really understands QM", that's
    more accurately the problem, as I also understand it.

    >
    >
    >>> Do you do closed-form Maxwell's Equations on every circuit? Or full EM
    >>> simulation?

    >>
    >> And you don't?
    >>
    >> I do on every single board I make. Not closed-form, but open-form
    >> approximation, qualitative accuracy. Implemented in wetware, too.
    >> Works
    >> very well.

    >
    > Have you solved the Schrödinger wave equation for any of your systems.
    > Only then will I call you a real engineer ;)
    >
    >
    >> Are you aware that ~20nH is ~86mm of 50 ohm, 0.67c coax?
    >>
    >> Assuming the headers pictured are 0.1" centers, the cores are roughly
    >> T37
    >> size ferrites, a bit thicker than usual. I get 14mm for the length of
    >> a
    >> single turn on a regular T37, so it might be closer to 18mm per turn,
    >> maybe 20mm with coax thickness. That's 60mm total length, or 14nH.
    >> The
    >> soldered connections and board traces have almost as much, depending on
    >> if
    >> there's a ground plane just out of sight or not. But by then it's not
    >> mutual, which is all the more reason it's not LL you're supposing
    >> about.
    >>
    >> Actual performance will show helical resonator action starting around
    >> 1GHz, which is what the under-hump on your leading edge comes from.
    >> And
    >> probably other nasties if you tested it with a ps generator rather than
    >> the "sub-ns" this particular device produces.

    >
    > Hey, want to help me design a LF shielded loop antenna from coax?


    Sure! My work is done:
    http://vk1od.net/antenna/shieldedloop/
    Well, maybe not *my* work, but... helpful nonetheless. Lots of excellent
    analysis on his website.

    Tim
    Tim Williams, Nov 5, 2012
    #20
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