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

Re: More Secondary Research (fwd)



---------- Forwarded message ----------
Date: Tue, 25 Feb 1997 09:15:18 +1200
From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
To: tesla-at-pupman-dot-com
Subject: Re: More Secondary Research (fwd)

Rick,
         I'm having a bit of trouble understanding....

>  I have found in the past that sticking two well calculated 1/4-
> > wave secondaries end to end and expecting the combination to resonate
> > at F/2 doesn't happen. I forget whether the frequency was higher or
> > lower than expected. I would like to nail down what's needed to
> > predictably calculate the resonant frequency for these systems. We
> > have been very successful for 1/4 wave systems and I see no reason
> > why this couldn't be done for 1/2 wave as well.
> >      If anyone has ideas for things they would like me to look at in
> > either system, please let me know.
> > 
> > Regards,
> > Malcolm
> 
> -- 
> Malcolm,
> 
> Perhaps this is just ocean foam, but how does the system know that you
> want to operate at half-wave and not at a higher freq quarter-wave freq?
> I realize that the match between pri capacitance and pri inductance
> should spell out a particular freq, but if you're going to limit the
> thing to half as opposed to quarter wave freq, wouldn't some sort of
> bandwidth limiting be required in addition to the normal specs? Perhaps
> I'm not being clear (hell, it's not completely clear to me!) but it
> seems that a whole new mathematics and design approach would be
> necessary.
> 
> 
>    Rick Holland

It has nothing to do with the primary values (which can be tailored 
for any desired frequency) but rather the way it is coupled into the 
secondary and the way the secondary is terminated. This is the 
defining bit. We are going from a monopole (1/4 wave) - single whip 
aerial, to a dipole (1/2 wave) - c.f. TV aerial. A typical halfwave 
configuration can be a single secondary coupled to the primary 
halfway along its length. As I say, I first measured a single 
secondary as a 1/4 wave resonator with one end grounded and then lay 
it on its side and coupled into it with an untuned primary (to get 
rid of coupling artifacts) halfway along its length. From memory it 
resonated at a higher frequency than I would have expected. This may 
be shades of removing a rather large object (earth) from being 
connected to one end which means a drop in capacitance for the total 
structure. In fact, it is probably that simple. A 1/4 wave connected 
secondary whose earth is removed also exhibits self-resonance at a 
much higher frequency as its preferred vibrational mode changes to 
1/2 wave (symmetrical end loading). I think when the earth is 
disconnected, not only does the capacitance distribution along the 
coil change but its interturn capacitance becomes much more prominent.
It is no longer working against the huge capacitance that ground 
represents.

I'll check this out in due course.
Malcolm