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In article CoC6j.3689$581.3625@trnddc04,
"Dale Parfitt" wrote: W8JI's view, as I understand it, is that small shielded loops are no less susceptible to local noise in virtue of their shielding, since the shield, in his view, is part of the antenna. It's probably worth pointing out that, even if this is true, it is still consistent with the view that small loops pick up less noise than other types of antennas in virtue of their directional characteristics. I guess W8JI would then maintain that a shielded loop would be no less susceptible to local noise than an unshielded loop, since in this case both antennas enjoy the benefits of directionality; but he isn't commited to denying that loops are quieter than, say whips when all things are considered. Is this correct or am I missing something here? Correct. Here it is from VE7SL perhaps more concisely: Please note that a 'shielded loop' will not do anything to improve local noise problems that any other type of loop (such as a multi-turn air core loop) might do. Don't confuse the 'shielded' nomenclature with 'noise shielding' as this is not the case. Like any other type of loop, it can be used to null nearby noise sources or signals or turned to enhance desired directions. The shielded loop might more properly be called a 'two-turn' loop or a 'close coupled' loop as this more accurately describes it's behaviour. In actual operation, it is the shield itself that is the active antenna element. Signals picked up by the shield are coupled into the inner conductor, which in turn are coupled back to the receiver via the preamp. The loop is capable of good nulls on both groundwave and skywave signals. The more 'balanced' the loop is (gap placed at exact center), the more balanced the nulls will be. This is wrong. I already explained why. Go back and read the part of my post you cut out of the thread. You are being to general in the description of shielded. -- Telamon Ventura, California |
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