[Prev][Next][Index][Thread]

Re: This 90 deg phase shift business


Hi Terry,

I have been trying to resist the temptation to get involved with this
transmission line argument,  because I don't have much experience in this
field,  and the Tx-line maths is a little heavy for me too ;-)

However,  your challange was too tempting for me to resist.  After all,  I
have a scope, resonator, and a function generator at hand...

> So give it a try and tell me what's wrong.  I think if I did all that
RGLC
> transmission line stuff I could explain the 5 degree phase shift (as I
have
> before) but there really isn't much that can go wrong with this test and
I
> invite anyone to give it a try...

Well,  the funny thing is that I just did the test,  and I think I saw a
90 degrees phase shift between the E-field at the base feed point and the
E-field around the toroid.

Now I know this is not what you and others have observed,  so I have
likely made a gigantic blunder somewhere.  If so tell me where I went
wrong ;-)

I took a resonator with toroid,  and base fed it straight from my function
generator.  (Unfortunately this unit only has square wave output
available,  my other unit is at work :(  I don't know if this affects
anything ?

I put a piece of wire in scope channel Y1 and wrapped this around the wire
feeding the base of the secondary,  and got a volunteer to hold a scope
probe from channel Y2 near the toroid.

I then adjusted the frequency to get maximum level on Y2 (resonance !)
The sinewave voltage surrounding the toroid seems to show a 90 degree lag
when compared to the fundamental of the square wave driving the base of
the resonator.

I don't know if using a squarewave to drive the resonator makes the test
invalid.  I do know that the resonator still draws a sinusoidal current
though.  In fact the heavy sinusoidal current draw caused the flat
portions of the squarewave to sag under load !

Take a look at these pictures:

www.staff.ncl.ac.uk/r.e.burnett/90deg1.jpg
www.staff.ncl.ac.uk/r.e.burnett/90deg2.jpg
www.staff.ncl.ac.uk/r.e.burnett/90deg3.jpg

I have always thought of the TC secondary as a series resonant lumped
tuned circuit.  ie. Vsource, L, C, and R all in one big series loop.
At resonance the current is in phase with the applied Vsource.
Surely the individual voltage across L or across C must be out of phase
by 90 degrees when compared with the applied voltage in order for the L
and C to keep their properties.  CIVIL and all that ?
Would you not expect a 90 degree shift for a lumped LC model ?

I would be interested to hear your views.

Sorry if I'm showing my ignorance,  as I've just joined this thread.

							Cheers,

							-Richie Burnett,