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#21
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Anybody following the Dallas Files
On 7/14/2011 11:20 PM, Richard Clark wrote:
On Thu, 14 Jul 2011 19:31:17 -0500, wrote: Sounds like you didn't look at the site so "what is left unsaid." Hi Mike, As I said, nothing there but a vague suggestion of the topic heavily cloaked in an admonition. Yes, I'm looking a steerable receive only arrays for the AM broadcast band. Myself, I want one that will fit on a 150ft lot. Is that 150' on a side? 150' long? There are any number of ways to construct variable delay lines. A little bit of computer control will pull their outputs together to form beam steering. For receive only, and moderate bandwidth, then digitizing the multiple antennas and doing the phasing in software is probably the easiest approach. Essentially infinite variability, you get "true time delay" as opposed to phasing (the latter is inherently narrower band, although for AM BC band, it might not make any difference.. 150 ft is a tiny fraction of a wavelength). Planting the antennas is simple and allows for testing of any of those many ways to construct variable delay lines. Those designs themselves have various trade-offs for issues you need to prioritize and pronounce. The antennas don't need to be in any particular, regular pattern as that would be accommodated by computer alignment. If you choose to go manual steering, with analog variable delay line designs; then, yes, having a regular pattern of element layout would reduce complexity. How many antenna elements? At least three, I would suspect. From there on it is a matter of how well you can resolve the various delay angles for steering a broad beam angle. Increase the number of elements and the beam angle gets progressively tighter. You don't say how much directionality you want, but it will be intimately correlated with this count. In general, you can place N-1 nulls with an array of N antennas. Broad nulls (in angular extent) are done by stacking multiple narrow nulls. For AM BC band (which is like 160m ham band), gain isn't a big deal, you'll be interference and atmospheric noise limited. The delay lines will have to be tolerant of mutual coupling - better yet, they should not perturb the existing mutual coupling at all. Good isolation amplifiers between each element and its delay line before going to a summing amplifier would seem a solution. Tracking between delay lines will affect beam width. More elements will require tighter tracking. The usual scheme is to use a lossy short untuned antenna and a FET pre-amp. There are several nice designs out there, or you can buy them off the shelf. http://www.amrad.org/projects/lf/actant/ is an example In the end, they all comprise the same fundamentals. If you cannot support a symmetrical design, that is your primary limiting factor. If you can digitize the delay lines, then symmetry can be synthesized and the antennas can be placed physically anywhere limited only by the resolution of digital sampling rate. And the dynamic range of the amplifier/digitizer. 73's Richard Clark, KB7QHC |
#22
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Anybody following the Dallas Files
On Sun, 17 Jul 2011 13:49:46 -0700, "Sal" wrote:
"amdx" wrote in message . .. snip This all seems odd to me. I had no problem getting admitted, he works with several hams regarding his antenna systems, so it's not about hams. I think he has some great research using single, dual and quad phased Flag or Delta antennas. There's also info on building a circuit for adjustable phasing of two antennas. So get another email address and just say you have an interest in improving your AM radio reception. Mikek But, yet, I got turned down again, even though I fully complied with his directions. The problem is that I politely added my opinion that his methodology for rejecting his group's applicants had a flaw in my case. (He had earlier explained some of it to me in a thoughtful and candid private email.) Obviously, I should have kept my opinion to myself. I live and learn. He responded to me with a curt one-line private email saying that the flaw was in _my logic_. From that, coupled with his third rejection two minutes later, I conclude that the mere mention of anything negative is an instant deal-breaker. He had earlier described trouble he'd had in his group with people he termed "bad boys." It's much easier to be dubbed one of his "bad boys" than I would have guessed. Wow! Yes, I could try to trick him with another email address; however, since I'm not welcome at his front door, why risk the humiliation if he catches me prying open a back window? I'm already somewhat annoyed at myself for this missed opportunity. Why make it worse? OK, so the final score is Dallas 3, Me 0. Game over. *sigh* Ya shoulda just kept your mouth shut rather than call him out on his "flaw" telling him you you don't respect him and just have to have the last word. His not allowing members posts should have given you a clue he is ultra anal. The outcome was predictable. Ya shoulda kept your mouth shut. Oh yeah, I got in too. |
#23
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Anybody following the Dallas Files
"Restek" wrote in message ... snip Ya shoulda just kept your mouth shut rather than call him out on his "flaw" telling him you you don't respect him and just have to have the last word. His not allowing members posts should have given you a clue he is ultra anal. The outcome was predictable. Ya shoulda kept your mouth shut. Oh yeah, I got in too. Noted. "Sal" |
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