Blind simulation without understanding

That's why I got the SignalHound USB spectrum analyzer so I can schlepp it in a carry-on bag. Plus the tracking generator, not so much for filters but to be able to gauge the attenuation of undesired noise intrusion paths.

If this IBZ sampling box really does 8GHz and the risetime is well under

you're

algebra and

whatever, I

Yep, those KABOOM!, one-thousand-one, one-thousand-two, one-thousand-three, one-thousand-four, one-thousand-five, one-thousand-six, CLANG! can be quite scary. I've experienced a couple of those of my own :-)

Trying to remember now, back in the '60's, we had a whole AZ town disappear when a community propane tank caught fire. TV crews a mile away filming the fire were bowled over by the blast :-( ...Jim Thompson

Unless the Romans built it, then it does.

I've owned old houses and new houses. The new ones are better.

John

Could've fooled me, an oscillator without feedback.

Tim

his

and

se

In the UK they have much lower ceilings which makes the room proportions a bit odd.

California is unusual. The earthquake risk means that houses have to be built to a code that got a lot more stringent after 1906.

-- Bill Sloman, Nijmegen

Obviously there's feedback of a sort, but not of a kind where you could fiddle with the phase shifts.

-- Bill Sloman, Nijmegen

and

whatever, I

I tightened the big nuts under there to the point where I'd think any more would break them and this #%^!! plastic junk still leaks. Unusual shapes, tough to buy anywhere, the usual.

So I guess I'll have to try pipe dope now. Great. Just great.

Actually, it didn't. The codes got serious after the Loma Prieta earthquake in 1989. Our house was built in 1992. It has massive concrete foundations, steel beam framing, and has structural plywood shear walls.

John

Just because the loop is closed doesn't mean the differential equations aren't there. You can gain access easily enough by controlling gain or bias (manipulating the voltage or current into the base supply, or varying the feedback voltage through various methods: pot, variac, old school rotating-axis "tickler" coil, etc.).

For instance, a high impedance bias supply could allow the base supply voltage to vary (large resistance or CCS, with servo if required), and the V-I characteristics would then be easily observed (impedance, step response, squegg damper "best values", etc.).

Tim

testing on

is

no

Last time i was pounding Mathcad i was doing a simulation with it. Got the job done too. I found the user interface to be fine, just very different from everything else i had ever used, well until recently, Macsyma is rather similar.

?-)

They are, but the fact that you get squegging with bipolar transistors and not with MOSFET switches makes it fairly clear that the feedback isn't driving the squegging in any way that would make it sensible to think about manipulating the feedback.

What happens with a too-high feed inductor is that current being fed into the centre-tap overshoots at start-up so that the voltage at the collector/drain of the "off" switch goes below the supply rail (which you can see in the simulations), inverting that switching transistor.

In the simulations that overshoot dies away, and the circuit settles into stable oscillation. In real life - but only with bipolar switches

- it doesn't and it seems more sensible to blame something in the subtleties of the behaviour of the inverted bipolar transistor rather than the differential equations.

-- Bill Sloman, Nijmegen

I haven't tried it since DOS days ;-) ...Jim Thompson

The transistor versions often have a bypass cap in the base bias circuit. The signal swing is rectified by the bases and charges that cap. All that adds another dynamic element to the loop.

Mosfets don't have base current.

John

Don't worry. It's not a problem that's easy to understand. Peter Baxandall only mentioned it in a footnote, which meant that he didn't feel that he understood it either.

-- Bill Sloman, Nijmegen

testing on

born

And

is

no

paper

thought

design.

I find the GUI version a lot easier to deal with. I don't have to remember all the "abbreviations" and their usage rules. If i can find my sim and a 'puter to with Mathcad loaded i will make a pdf and send it to you. Unless you ask for it this will be low priority.

?-)

Thanks! At your convenience. It's not a biggy, I can solve transcendental equations with PSpice, just ducky ;-) ...Jim Thompson