I appreciate the link! I have tried the dual coil on one rod approach, and I
did get it to work fairly well. There is some interraction between the two
coils, so I decided to go with the one range per band approach. This also
eliminates the stray capacitance and inductance that can occur when
switching the coils. I even tried the tapped inductor approach, but that is
another can of worms. I ran into self resonance problems in the MW coil that
were caused by the LW coil.
As an example, the MW coil exhibited self resonance at 950kHz. When
grounding the LW coil, the self resonance changed frequency to 850kHz. If
this approach is used, the ferrite rod needs to have a variable density,
where it would have a very low permeability in its center, and have the
permeability increase at each end. It would be easier to use two loopsticks
mounted end to end, using a delrin coupling to that the two rods don't come
into physical contact with each other.
Using the separate loopstick approach, I noticed that placing two loopsticks
within 5 inches of each other would not only detune the desired loopstick,
but it would also cause distortion in the directional characteristics.
I notice that the German radio manufacturers have been using the dual coil
approach (LW and MW on the same rod) for years, but my experiments indicate
that this approach appears to be a compromise.
I am thinking about winding a loopstick that will cover from 2MHz to
approximately 11 or 12MHz today. I don't think there will be any directional
characteristics above 5 or 6MHz, because of the multipath effects that can
occur because of ionospheric scatter, but it is worth a try.
I should be doing the formal board layout for the final unit later this
week.
Pete
Pete [KE9OA],
Some where I read ? saw ? a LW and MW Ferrite Rod Antenna
with both Coils on the same {single} Large {Long} Ferrite Rod.
IIRC - It had a Single Large Coil in the Center and a Pair {Two}
of Balanced Coils at each End of the one Ferrite Rod.
Believe the Ferrite Rod was around 12 Inches long.
MW Loop Source Book -compiled by- Steve Whitt
http://www.mwcircle.org/res-mwloop-book.htm
don't know if that helps any - it3c ~ RHF