Quote:
Originally Posted by CraigS
I may have misjudged the Relaxation Oscillator thingy also.
Alex forwarded us a paper which contained a model of transmission lines.
What's that got to do with a Relaxation Oscillator ? I asked.
Apparently what they're saying is that a pulse entered into that system bounces up and down the transmission line (like what caused power blackouts in the Northern US). The pulse continues bouncing back and forth between impedance boundaries simulated by the combination of modelled elements in the transmission circuit model. This then, starts to emulate the behaviour of a Relaxation Oscillator. Mind you, each time the pulse rebounds, it loses energy and eventually dies out due to losses in the transmission line media.
I'll have to re-read the Peratt/Healy paper again on this one.
This post should also be on our 'Primordial Magnetic Fields' thread. I might copy it over there, for the record (& for Bojan to shoot me down on this .. oh you can, too  )
.. I'm not saying that any of this makes sense, yet .. I'm just seeing that there may be a lot of miscommunication going on as the Electrical speak comes together with AstroPhysics .. not of our making .. it's up to the PC authors to have explained all this much more clearly .. and they haven't.
Cheers |
You didn't misjudge anything.
For an 'oscillator' to be called an oscillator, you have to have amplifier and feedback.
The feedback must be of such a nature, that the 'open loop gain' is bigger than 1 (one), and the phase is close to 0° (or 360°)
If you don't have those elements. you don't have an oscillator.
Now, gain means, there must be an input of power from somewhere (even internal power source will do) to sustain oscillations, otherwise, as you pointed out, they will stop after couple od periods, sometimes even sooner (as in case of relaxation oscillator .. which, BTW, doesn't have frequency selective circuit, like transmission line.. it has TWO amplifiers, for phase shift of 180° each).
ANY model of the pulsar must firstly explain the unusual frequency stability - as we (RF electronics engineers) know, oscillators are very unstable circuits in terms of frequency, especially when Q factor of the circuit goes low (high losses in the circuit... which is radiation of energy in any form from the system).
As I said before, and I am repeating now, in Peratt's there is NOTHING that looks like an oscillator.
It is more like very crude and simplified equivalent circuit that tries to model currents in ionised environment over large distances (up to couple of hundreds of thousands kilometres.. to explain relatively low pulse repetition rate - milliseconds to seconds).
The only thing that looks like active element is that variable resistor... but there is no feedback path.. and energy source is not determined.
I were the teacher in high school, noone with paper like this would pass the exam as far as I am concerned.