"Uncle Peter" wrote in message
...

"Dave" wrote in message
...

"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



For a broadband step up, you'd be better off using a ferrite core untuned
transformer or balun.

Are you using this between the coax and a coax leadin? Or, between the
antenna and RF antenna jack on the receiver?

Pete

Pete


I am doing this inside of the active antenna case, using the coils used for
tuning the tank circuit. It's really kind of an unusual setup, I gather. I
am trying to use the resonance of the coil, which is in parrallel with my
tuning capacitor, to set up a sympathetic signal in the second layer on
that same coil, and feed this sympathetic signal to my first stage of
amplification. That's the step-up transformer part. The whole thing just
resonates at a higher frequency than I anticipated. Thus my original
question: has anyone heard of this before, and what is it called/where can I
find more info on the subject. Fortunately it still allows me to pull in my
target shortwave station, but it's at the bottom of the tuning range rather
than the top.

Thanks for your help,

Dave