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Re: Tesla Coil RF Transmitter



Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Malcolm,

I've been thinking about the original statement and I'm thinking there might be an element of truth in it. An RC network can not duplicate any transfer function, but I'm thinking that it might be able to emulate the magnitude response (attenuated) and only for sinusoidal exitation. The phase response would be a different situation. If the RC network were to be excited by a delta function or unit step function, there would be different responses.

Gerry R

Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>

On 27 Sep 2005, at 21:51, Tesla list wrote:

> Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
>
> To all,
>
> Is it not true that RC networks can only have poles on the real
> axis.  How do you get imaginary pole/zeros???
>
> Gerry R.

Agreed (first sentence). You don't (second sentence). But you can
certainly produce a bandpass/bandstop function without the use of
feedback and it does *look* like a resonant circuit if (a) you
consider just the frequency response and (b) realise that energy is
being dissipated rather than stored.

Malcolm



> >Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>
> >
> >Hi Ed,
> >
> >On 27 Sep 2005, at 13:37, Tesla list wrote:
> >
> > > Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>
> > >
> > > At 11:17 PM 9/26/2005, you wrote:
> > > >Original poster: Ed Phillips <evp@xxxxxxxxxxx>
> > > >
> > > >"Excellent point, and a good example of a frequency selective
> > > >system that's band limited. Hmm, though, can one create an
> > > >arbitrarily sharp cutoff with only RC?  I think not, off the top
> > > >of my head."
> > > >
> > > >         We used to have a guy at Hughes named Lou Weinberg who
> > > >         had the
> > > >reputation of being a real expert on network synthesis.  I heard
> > > >him say that, using only PASSIVE RC circuits, it was possible to
> > > >synthesize any transfer function shape if the loss were allowed
> > > >to be arbitrarily large.  Don't know if it's true or not.
> > > >Certainly with a little feedback you can get arbitrarily sharp
> > > >response.
> > > >
> > > >Ed
> > >
> > > I've thought a bit (and am too lazy to go find my copy of Mason
> > > and Zimmerman, which I'm sure would have the answer)..
> > >
> > > I think you're right.  I was having trouble figuring out how to
> > > get sharp nulls (or more properly, sharp cutoffs).  A series of RC
> > > networks can get you more than 180 degrees of phase shift, and if
> > > you sum the 180 and the 0 path appropriately, you get a null. One
> > > can always string up multiple nulls (at different frequencies) to
> > > get what you need.
> > >
> > > I don't know that you can get the classic resonance curve, though
> > > (except with a huge number of sections).
> >
> >Twin T and Weinbridge networks spring to mind in connection with both
> >of those and I'm sure that's not the end of the story. I predict that
> >someone attempting to disprove the hypothesis about generating
> >transfer functions using only RC components (losses taken into
> >account) would have a very hard time.
> >
> >Malcolm
> >
> >
>
>
>
>
>