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

"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

"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

"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

"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

"Dave" wrote in message
...


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


Hi Dave

Then in effect, you are trying to match a lower impedance to a higher one
since you are trying to increase the voltage gain.

Without knowing the active antenna you're attempting to use, it is kind
of hard to determine what advice to offer. I think you mentioned a 100 foot
long wire... That would have a much lower impedance over the HF range
than a 3 foot whip. If you just want voltage gain, use several turns on
the bottom of the coil for coupling the antenna to the tuned circuit.
The tuned circuit will provide the voltage gain. You will reach a point
where the active antenna will be prone to overload, even with the tuned
preselector input.

Pete

"Uncle Peter" ) writes:

Without knowing the active antenna you're attempting to use, it is kind
of hard to determine what advice to offer. I think you mentioned a 100 foot
long wire... That would have a much lower impedance over the HF range
than a 3 foot whip. If you just want voltage gain, use several turns on
the bottom of the coil for coupling the antenna to the tuned circuit.
The tuned circuit will provide the voltage gain. You will reach a point
where the active antenna will be prone to overload, even with the tuned
preselector input.

I always thought the concept of an "active antenna" was that you had a
short whip and barely loaded it down. The whip itself is connected
to a very high impedance point, and then the active components are
there to transform that into a lower impedance for the receiver.

You basically see the idea in old car radios, where the whip was
connected across the tuned circuit at the input. If you didn't use
the right cable to connect it to the antenna, and if you didn't use
the trimmer to adjust things to compensate for that cable, you'd
lose a lot of signal.

Then solid state devices came along, and that made it much easier
to do the transformation, since they took up less space and didn't
need filament voltage.

A preamp or even preselector is not the same thing as an "active
antenna".

Michael VE2BVW

On Jun 1, 5:35 pm, "Dave" wrote:
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

The reactance of the coil at 3.7MHz is about 375 ohms. Your long
antenna will likely put an impedance across that tank that's on the
same order, or maybe lower, impedance. That will pretty much kill any
resonant peak you got from the coil and capacitor.

You should start, perhaps, by realizing that what you are looking for
is generally not the largest voltage from the antenna, assuming you
can add whatever amplification you want, but rather the best signal to
noise ratio or the lowest distortion. In fact, atmospheric noise is
so large at these HF frequencies that it doesn't take much of an
antenna to pick up more of that atmospheric noise than the receiver
will contribute, assuming a decent receiver. Making the signal larger
just increases the distortion and the chances that strong signals will
cause distortion that covers up the weak ones.

There IS an advantage to having sharply resonant circuits in front of
any gain stages in the receiver, because you can use them to get rid
of unwanted signals, and preferentially select the signals you want to
listen to. But to do that, you need to think more carefully about the
design of the resonant circuit.

You may in fact find that it works a lot better if you couple your
antenna to the tuned circuit (your toroid core and capacitor) rather
loosely, like with very few turns--perhaps a single turn-- through the
core for the antenna connection. Even back in the very early days of
radio, the advantages of a sharp resonance achieved by loose coupling
to a resonant circuit were understood: they used something called a
"loose coupler" that let them adjust the coupling from the antenna to
the tuned tank/detector. For best selectivity, couple lightly, just
enough to get a usable signal. That means coupling the receiver input
lightly to the tuned circuit, too.

Cheers,
Tom

"Uncle Peter" wrote in message
...

"Dave" wrote in message
...


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


Hi Dave

Then in effect, you are trying to match a lower impedance to a higher one
since you are trying to increase the voltage gain.

Without knowing the active antenna you're attempting to use, it is kind
of hard to determine what advice to offer. I think you mentioned a 100
foot
long wire... That would have a much lower impedance over the HF range
than a 3 foot whip. If you just want voltage gain, use several turns on
the bottom of the coil for coupling the antenna to the tuned circuit.
The tuned circuit will provide the voltage gain. You will reach a point
where the active antenna will be prone to overload, even with the tuned
preselector input.

Pete



Hey Pete,

The active antenna is a home-built MFJ-1020A, which has a short whip and an
input for an external antenna. The amplifier has the gate of a JFET
(2N5486) as the input for the first stage of amplification. I can post a
schematic to ABSE if you like.

After reading your last post, I think I am beginning to understand what you
mean, about matching impedances. This subject has always been a tough one
for me, but it interests me, and now I have a reason to study and learn it.
I had no idea that was what I was trying to do.

So, it sounds like I am trying to match a low impedance signal source (the
longwire antenna) to a high impedance input (the amplifier.) Is that
roughly correct? If so, any idea on where I can find more info on impedance
matching?

Thanking you very much for your help...

Dave

"K7ITM" wrote in message
oups.com...
On Jun 1, 5:35 pm, "Dave" wrote:
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

The reactance of the coil at 3.7MHz is about 375 ohms. Your long
antenna will likely put an impedance across that tank that's on the
same order, or maybe lower, impedance. That will pretty much kill any
resonant peak you got from the coil and capacitor.

Man, I think you are right on the money with this. I get the signal, but
very little ability to "tune" it in, as if the resonant "peak" is very low
(my understanding.)

You should start, perhaps, by realizing that what you are looking for
is generally not the largest voltage from the antenna, assuming you
can add whatever amplification you want, but rather the best signal to
noise ratio or the lowest distortion. In fact, atmospheric noise is
so large at these HF frequencies that it doesn't take much of an
antenna to pick up more of that atmospheric noise than the receiver
will contribute, assuming a decent receiver. Making the signal larger
just increases the distortion and the chances that strong signals will
cause distortion that covers up the weak ones.

I am getting more signal than noise, compared to operation without the
active antenna, but it's not exactly "prime".


There IS an advantage to having sharply resonant circuits in front of
any gain stages in the receiver, because you can use them to get rid
of unwanted signals, and preferentially select the signals you want to
listen to. But to do that, you need to think more carefully about the
design of the resonant circuit.

Yes, yes, that is what I am attempting to do. I am just such a newbie to
RF...


You may in fact find that it works a lot better if you couple your
antenna to the tuned circuit (your toroid core and capacitor) rather
loosely, like with very few turns--perhaps a single turn-- through the
core for the antenna connection. Even back in the very early days of
radio, the advantages of a sharp resonance achieved by loose coupling
to a resonant circuit were understood: they used something called a
"loose coupler" that let them adjust the coupling from the antenna to
the tuned tank/detector. For best selectivity, couple lightly, just
enough to get a usable signal. That means coupling the receiver input
lightly to the tuned circuit, too.

My best results come from using an alligator clip with a foot or so of solid
wire soldered to it, and clipping to the center conductor of the output from
the active antenna while wrapping the wire around the whip antenna of my
Sony 7600GR portable SW radio. This gives me a slightly clearer signal,
even if it is not as loud as pluging the output into the external antenna
connection of the radio. One thing I suspect is that I am using the wrong
type of coax (RG-59). I believe my coax is 75 ohm, and what I probably need
is 50 ohm. Does that sound right? Or am I wrong here?

Thank you so much for your help. I have been working on this for a while,
and think I am getting close to achieving my goal.


Cheers,
Tom