Al wrote:
----- Original Message -----
From: "N9NEO"


I posted a few questions about loop antannas but they didn't get
answered over on Yahoo loop antenna group so I will try here.

That particular Yahoo group is generally very responsive and knowledgeable.
I find that if you ask too many questions at one time, the reponse is lower
than if you keep the questions down to 2 or 3. Break down your questions and
you will probably get a better response. As I said earlier, they are good.

So now the nice null that you have along the axis
of the loop is destroyed because the ferrite is aligned there. Is this
correct?

If you want to use both antennas, place your receiver into the loop in such
a way that the two antennas are mutually aiding each other (they should be
locked together in this position) and keep them this way. In other words, if
you rotate one antenna in one direction, the other one should also rotate in
the same direction.

2) Where should the tuning capacitor be located physically relative to
the loop? I would suppose the best place to put the capacitor would be
directly on the coil. Total distance would probably be less
than a foot. So is this a good plan?

Yes, keep it close to the coil but don't go crazy trying to keep it extra
short. Try your plan plus or minus a foot and you will not hear a
difference.

3) I have three wiring options as far as the variable capacitor goes.
One gang, two gang in parallel, or two gang in series. Right now I use
two in parallel near the bottom end of the band, and one gang nearer
the top.

Sounds complex. Do you have to tune both capacitors in order to resonate the
antenna? Simplify by keeping the capacitor(s) near the easy access point
only. If you can tune your antenna across the range you want (which may be
difficult with just one variable capacitor) then you have accomplished your
goal.

5) I am considering going from 20 Gauge magnet over to litz wire.

I suppose in theory there should be an improvement, but nothing that you
will be able to hear. It's like comparing a million dollars to a
million-and-one dollars. Mathematically the million-and-one is better, but
what can you do with that extra dollar that you can't do with a million?


6) I am also considering the varactor diode tuning approach. Comments?

I also have a loop antenna, for the LF band below 550kHz, that I would like
to tune remotely and have considered varactors. The negative comments I read
about varactors is that because they are diodes, there will be some
rectification effect on incoming signals resulting in unwanted signals. I
have not tried them so I don't know how they will work. If you come up with
a workable solution, please let us know.

The diodes have a reverse DC bias, so there is no rectification of the
RF signal. Now the Q of the varactor might be an issue.


Thank-you for any guidance you can give with this project.
Regards,
NEO

No problem. Keep us posted on your findings.

Al KA5JGV
San Antonio, TX
http://home.satx.rr.com/ka5jgv/