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What's this inductor doin'?

Discussion in 'Electronic Basics' started by Steve Evans, Oct 3, 2004.

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  1. clifto

    clifto Guest

    You owe me a keyboard to replace the one that just died under three
    quarts of drool.
  2. Steve Evans

    Steve Evans Guest

    In my limited experience over the lats 22 months Iv'e read both (well
    looked through both!) and they aer both highly infromative books. Id
    just give the edge to the ARRL version, it's more readable and has
    more coentent, but hte RAdcom version is still well worlth having on
    the shelf. I do'nt see any problem with the Brits anachronistic
    attachment to valve gear.
  3. J M Noeding

    J M Noeding Guest

    I is really a myth, TV sets were fully transistorized in Europe
    compared to USA by several years
  4. Steve Nosko

    Steve Nosko Guest

    Steve (Evans),
    Correct me if I am wrong (like I need to say this here, eh?)
    I believe the underlying basis is the collection of loop / node equations
    used (by Engineers) to model circuits. We know the behavior of resistors,
    inductors and capacitors and have mathematical models for them. To this we
    add the active devices, etc. and develop an "engine" which does all the
    calculations for us. [[we used to do them by hand/slide rule -- yes, I am
    included in this we]]. These loop and node equations provide us with a
    mathematical model of the behavior of electronic circuits. If done
    carefully, this is a general purpose model which applies to all the
    situations for which our component models are valid.
    Some time later there were bare engines into which we had to type the part
    values and node numbers (the sane things you can see in printouts from
    Spice). As computers got more powerful, schematic entry was developed. I
    believe these programs to be very useful, but as with any model or
    simulation, it is best to understand the limitations.
    Thre is an alternate method. It is also possible to derive equations for
    each type of situation and use these calculations each time you need to
    solve that type of problem. I am sure you are familiar with the equations
    for things such as parallel capacitors and resonance and so forth. These
    are specific solutions of the properties of components in those specific
    From some postings here I get the idea that Reg is providing various
    "calculators" in the form of computer programs for hams to use to
    solve/design various circuits. Not one thing wrong with either this or the
    general type of software...Except that the limitations argument applies to
    all calculations and it is our responsibility to determine whether or not
    our situation is adequately covered by a particular math model.
    I am also not familiar with the programs mentioned here (except to have
    heard the names), except for OrCad's PSpice ver 9, which is relatively easy
    to use (for me) and provides results adequate for my purposes--not to
    mention the fact that I was given a CD with the student sample version on
    it). I was introduced to is by the department chair at the county college
    where I was asked to teach some classes and like it. I just draw a circuit
    and can then do various forms of analysis. I modeled a recent project and
    all worked the first time when I assembled the one and only unit. It was a
    simple RS-232 to Kenwood TH-F6A handheld interface.

    I agree 100% with Reg in that a circuit simulation program is not intended
    to *teach* circuit theory, That needs to come first, then the simulation
    tool can help us gain a better understanding by letting us try out the
    things we learn and "see" them happen with out having to collect all the
    parts and wire it up. I find it much faster to "assemble" a PSpice circuit
    and test my design ideas than go into my basement and collecting all the

    BTW it *IS* the cap AND diode which cause the negative voltage in the
    coupling circuit described so long ago...

    While I applaud your desire to understand how these "engines" work and
    perhaps build your own, I suggest that it is a most formidable task by any
    measure. If you understand the concept of loop and node equations then you
    know the math. Now figure out how to write software to handle any circuit
    and you have it...then there is the user interface...(what I believe is the
    most important [and most difficult to do well] part of any program)

  5. Roy Lewallen

    Roy Lewallen Guest

    When solving node/loop equations manually, it's generally necessary to
    resort to phasor analysis with its underlying assumptions, or Laplace
    transforms. The latter does have the capability of producing a time
    response. But the solution requires finding the inverse transform, a
    process similar to integration in that there's no single direct rule,
    and often it's impossible to find a solution except for simple cases.

    Computers can be programmed to solve complex problems numerically, using
    fundamental time-domain current/voltage relationships (such as the
    relationship V(t) = L di/dt for an inductor, or even more generally,
    V(t) = L di/dt + I dl/dt for a time-varying inductance). This is
    basically what SPICE does, and it's able to easily solve problems which
    are simply not possible to do manually, either because of the enormous
    time that would be required, or the impossibility of finding a reverse
    Laplace transform -- or its equivalent, the solution to a high-order
    differential equation if Laplace transforms aren't used. A google search
    on 'SPICE "time step" equations' brought a number of hits. I'm sure you
    can find an adequate explanation of the inner workings of SPICE among them.

    Roy Lewallen, W7EL
  6. john jardine

    john jardine Guest


    The simulators basically offer 2 types of direct analysis ...
    An "AC" analysis and a "Transient" analysis. Their answers come via
    different maths methods.
    Basically the much less useful 'AC' analysis examines all the wire
    connection points 'nodes' in the circuit diagram and enters the found
    components in 2 matrices. Each (square) matrix is sized to hold node^2
    elements. One is for 'real' components, the other for quadrature components.
    All non linear components in the circuit must first be simplified/replaced
    by linear equivalants (messy). Matrices are filled in a manner similar to
    kirchoffs loops anaysis. Reactive components entering the imaginary matrix.
    Ie lots of real/imag simultaneous equations need solving which is of course
    why the computer is handy.
    After they are filled the matrices are mathematically inverted to give a
    complete set of solved phase and ac voltage data for all the node points in
    the circuit. Nice for filters useless for oscillators!.

    The more useful transient analysis is similar to as you mention (Babbage's
    difference engine?) but based simply on the differentials V=L i/t and V=i/C
    and uses near complete maths models for the semicons or other non linear
    elements. Nodes examined in turn and time steps selected purely on the
    basis of how fast the results are changing. time steps can be a problem as
    too long and the final results get 'smeared out' hence phase lag artifacts
    cause overall loop stability problems.
    The TA is conceptually very simple and surprisingly easy and fun to
    programme for set piece or well observed circuits but gets *really* spagetti
    code messy if it is to work smoothly with any input circuit. Big problems
    can turn up getting the results to converge or balance and much progging
    effort is needed in this direction.
  7. john jardine

    john jardine Guest

    To me, Pat Hawker is the defining spirit of UK amateur radio.
    I've also picked up much fascinating stuff from his technical-topics and the
    mentions of his SOE work in WW2.
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