[Lowfer] 8 kHz VLF loading coil idea

[Bill Ashlock]

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.

> >How much open land do you have? You will be faced with the typical ground
> >radial problems and the need to have a lot of capacity in the top hat. 
>...
> >and your site has to be pretty free of trees.  No relief from the 'tree
> >effect' at these low freqs, as the trees still look electrically like a
>huge
> >distributed ~10K resistor and any small capacity coupling into them will
> >kill your antenna current due to reduced system Q.

>Yeah, that is the downside to a vertical...and I do have plenty of trees.
>The silver lining is they could make good supports for capacity hat 
>umbrella
>elements (if I decide to go that route). I guess you just have to work with
>what you've got.

Unfortunately I spent years in the Lowfer scene tring to get some descent 
antenna current on my many vertical configurations (Lyle will back me on 
this, because he ran many simulations for me). It wasn't until, in 
desperation, I tried a simple #12 loop (which wasn't supposed to work 
either) that I could finally get out some distance.

>I do have room for a pretty big cap hat, tree issues aside,
>and can arrange it so that at least none of them will be 'inside'/under the
>hat.

Plan for at least a 80ft min diam opening in these trees for your hat.

> >Have you considered a loop antenna placed over the top of any trees you 
>may
> >have? I admit that my first attempt at operating a loop at 9 kHz was
> >discouraging but have some areas to work on before I give up.

>I have thought about a loop too, and may very well still try it, especially
>if you or someone else gets good results so there is something concrete in
>terms of design to work from.

I'm very anxious to run my new BIG loop at 9k but have this other hot 
project going on that has to be completed first.

>Have you considered one of those Maxwell pulse-power oil caps, or a
>power-factor correction cap? Those should really take a beating. Don't know
>about the Q though...

Probably not too good. But 9k is a lot lower than 185k where my experience 
lies. Actually I used to design the yoke resonant circuit for monitors 
around polyester caps. So they need to be tried.

Bill

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