[Lowfer] 8 kHz VLF loading coil idea

[Ed Phillips]

Bill Ashlock wrote:
> 
> Jon,
> 
> >>Why not use a ferrite coil?
> 
> >I actually had thought of that first; I have a nice big color TV flyback
> >which could be modified for adjustable airgap tuning. However, I had
> >a couple concerns, besides the mechanical logistics of making the core
> >adjustable: A) Will it have enough inductance? (I don't know what
> >these typically spec at.) I'd need probably around a Henry, maybe more
> >since
> >tuning can only be done by decreasing inductance. I guess I'd have to
> >measure it with a cap and sig. gen. B) Will it take 50 watts? (or
> >thereabouts.) The secondary is wound with what looks to be Litz (from what
> >I
> >can tell of the bare 'ground' end) and it is pie-wound in nature so it may
> >have a fairly high Q. But I wonder if that fine wire can handle the current
> >that may be pushed through it? Truthfully, I'd rather
> >use it than a MOT, as long as it could do the job.
> 
> The core in these transformers is probably a good match for your loading
> coil from a power and inductance standpoint. You may have to remove all the
> windings, however, and add your own. You can wind the coil on a form off the
> C cores. My last 9k antenna experiment used the, medium voltage, yoke
> windings in a color flyback. I first removed the high voltage winding. I
> think the Q turned out to be ~ 100 and the inductance around a Henry. It
> would really help if you were able to obtain an LRC meter. My understanding
> of inductors, capacitors too, made a quantum leap when I finally broke down
> and bought one.

	If you use any form of ferromagnetic core be sure to calculate the
working flux density at the operating frequency and voltage; I have seen
a lot of "filters" proposed which couldn't work as planned because the
cores would saturate and generate very high losses.  It should be less
than perhaps 3500 gauss for typical ferrite materials.  Also be sure to
estimate the effective loss resistance under the operating conditions
and compare it to the RADIATION RESISTANCE of your loop or other device;
formulae are readily available which let you do this.  A Q of 100 sounds
too low by orders of magnitude! 

Ed

P.S. Prepare to be disappointed.