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. I've
condensed post some. Loops I have been playing with so far are
strictly for 500kHz -1600kHz. I know this is SW group so I think maybe
the info would be good for others that may want to experiment with
loops for SW too.

1) I understand that the common method to couple a portable radio to
the loop is to just stick the radio into the center of the loop.
Doesn't this method then tend to have directivity in two orthagonal
directions? In other words the loop will have a node in the North-South
direction while the ferrite rod will tend to be directive in the
East-West direction, because of the orientation of the ferrite rod
within to the Loop. 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? Maybe it might be good to couple signal in another fashion.


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. The capacitor is a heavy unit from a Heatkit
SB220 Linear amplifier, so it just doesn't want to hang anywhere. I
would like to mount it to the base of the loop and run some sort of low
inductance wire to the loop. Maybe a light gauge sheilded cable or lamp
cord - which would minimize the stray inductance between the tuning
capacitor and loop would be good. Total distance would probably be less
than a foot. I have found that alligator leads want to be twisted
tightly together in order for this thing to work. So is this a good
plan?

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. Should I add more turns to the loop and use a smaller
amount of capacitance. Literature I've read says use more turns and
this will also give more antenna gain. I know that more capacitance
will give me more Q, but not sure at this point if I need any more Q.
I know that V = N * dflux/dtime so maybe more turns means more volts.
I guess it's probably time to go review some detailed literature on
loop antenna design.

5) I am considering going from 20 Gauge magnet over to litz wire. I
would like to hear comments regarding this approach, and also who is a
good litz wire vendor if approach is worthwhile. I think maybe the
crystal radio peeps may have some input on this one.

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


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

Regards,
NEO