"Uncle Peter" wrote in message
...

"Dave" wrote in message
...
Has anyone ever heard of anything like the experiment I am currently
concocting? I have taken an Amidon T50-2 toroid form and wrapped it with
57 turns of #32 enamaled wire, giving it an inductance of 16 uH, then
wrapped over that layer with 150 turns of #36 wire. The first layer (16
uH) I am using for tuning my home-built active antenna, and am relying on
resonance to send a signal through the outer layer, which I *think*
should act like a step-up transformer for that signal. This layer is
grounded on one end, and feeds into the first stage of amplification on
the other. And it does seem to work, only the toroid seems to resonate at
around 10 MHz with my tuning capacitor set to 114 pF, when it should (I
thought) resonate at something lower, like around 3.7 MHz.

And like I said, the step-up transformer part does seem to work, but I
can't tune as low as I would like. Has anyone ever hear of anyone else
trying anything like this? If so, what is it called, and where can I
find info on the subject?

Many thanks for any help...

Dave

What are you trying to match? I suspect your secondary winding has
a lot of interwinding capacity that might be affecting it's operation.
For a ""step up", it might be easier, and more efficient, just to design
a pi or L matching network to do the transformation... Or, use
tapped windings on the coil used in the tuned circuit. Low impedance
at a lower tap point, impedance and voltage will increase on higher
taps..

Pete



Hello Pete,

I'm not actually trying to "match" anything, I am attempting to step up the
voltage of the incoming signal from my antenna (a 110' longwire use for SWL)
before passing it to my first stage of amplification. I think I see what
you mean however, this sounds like an impedance matching setup. And I
hadn't thought about the interwinding capacitance. Obviously, I am still
fairly new at this.

I saw a schematic in Joe Carr's Secrets of RF Circuit Design that used a
step-up transformer before the first stage of amplification, and that gave
me the idea for using my tuning inductors (toroids) with a second winding
that might act as a step-up transformer. And it does seem to work, just not
withing the frequency range I was expecting. My goal is to pick up Voice of
Korea here in Texas, at some level of intelligability. And I am a lot
closer to that than I was with the plain-jane tuning setup. Today I picked
up their 1500 UTC broadcast, which is something I have never been able to do
before. (Talking about how happy Korean children are...) It is still far
from perfect however...

Thanks for your input. More food for thought... With time, maybe I'll get
what I am looking for.

Dave