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Hi all,
I'm toying with the idea of an 'electronically rotatable' dipole setup. Consider: a dipole oriented N/S another dipole oriented E/W They cross each other at the mid-point of each, forming a big plus sign, like so: | | ----+---- | | If you feed the N/S dipole, you get an E/W radiation pattern. Similarly, if you feed the E/W dipole, you get a N/S radiation patter. If you feed the N/S and E/W dipoles simultaneously, you get a NW/SE radiation pattern (for example), and if you flip the feed of either one of them 180 degrees, then you get a NE/SW radiation pattern. So far, so good. Now for the fun part. If you feed one of the dipoles with a signal that is only 90 degrees out of phase (or 270 degrees), you can get radiation patterns that take of in the NNW/SSE or WNW/ESE directions, and if you feed the other dipole 90 or 270 degrees out of phase, you get NNE/SSW and ENE/WSW directions. What I am looking for is a circuit that can perform the necessary phase delays, without having to use miles of coax coiled up in the shack. Ideally, the circuit would be able to perform the phase shift on all (or at least several) ham bands, so that it could feed into a pair of fan-dipoles for operation on multiple bands. Anyone have any suggestions on just how to accomplish this? In the extreme case, you could have a continuously adjustable system, that would permit you to point the 'virtual dipole' in any direction at all, which might be useful when attempting to null out an interfering station off to the side of the desired signal. However, in practice, I suspect that the eight positions mentioned above would be sufficient to do the same thing (albeit with the possibility of somewhat more signal loss due to fixed aiming directions). I seem to recall seeing a quote in the ARRL Handbook (or the ARRL Antenna Book) from Roy Lewallen, indicating that there is no simple way to do this. Am I mis-remembering (or mis-interpreting) what I read? I know that the military does this sort of thing with radar systems, and has for some time. However, their budget is quite a bit bigger than mine, so perhaps their solution isn't 'simple':-) Any thoughts on this, anyone? Harry Gross |
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