"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