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On Sat, 2 Jan 2010 09:08:16 -0800 (PST), mr1956
wrote: I suppose my question is this: Is there a longer multiple of wavelength I can use for the impedance matching 75 ohm sections to develop a more practical design for what I need? Or, am I stuck with the 2.1" length due to the frequency? Hi Curt, To answer your last question first: you can use odd multiples (1, 3, 5, 7...) if your initial computation was correct. Consider, if your computation contains errors, they, too, will multiply. Computations aside, a receiver rarely needs exact matching when "close is good enough." Two 50 Ohm antennas in parallel or series are not seriously off. The mismatch loss would probably amount to less than 1 dB whereas your using two crossed antennas is in an effort to recover from the loss of polarization mismatch that can exceed 20 to 30 dB. As a practical matter, have you tried testing these antenna issues at ground level? There are certainly complications that ground proximity can introduce (reflection from ground being principle among them). As a first pass approximation, however, you can come to some feeling for many issues without having to loft anything into the air. Insofar as polarization mismatch goes, ground's proximity would tend to dilute my suggestion as ground and anything that is in proximity would tend to offer many reflections some of which don't come anywhere near your final application. 73's Richard Clark, KB7QHC |
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