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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 |
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