What's this inductor doin'?

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.

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

"Airy R. Bean" wrote in message news: snipped-for-privacy@uni-berlin.de...

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 circuits. 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 parts.

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

Airy, 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)

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

Steve Nosko wrote: >. . .

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. regards john

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. regards john