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On Fri, 21 Nov 2003 23:17:33 +0500, "John Doty" wrote:
|In article , "w4jle" W4JLE(remove this |to wrote: | | Believe what you will, the law of reciprocity will ignore your beliefs | and continue to function. | |1. It's only a "law" for scalar radiation (like sound), not vector |radiation (radio). To be sure, it's a fine approximation for most HF |antenna systems, but watch out a microwave frequencies, especially if your |antenna system contains a "circulator". Heh heh. When the guys from MIT come out to argue with you, you know you're in trouble. But fools rush in... I have made thousands of measurements in anechoic antenna ranges and I have never seen a difference between measuring s21 and s12. (Without the circulators, and accounting for mismatch effects of course) Where did I go wrong? |2. In the cases where reciprocity applies you would be correct to say that |it requires that the antenna directivity and efficiency are the same for |transmitting and receiving. It does not follow, however, that a poor |transmitting antenna is necessarily a poor receiving antenna. Efficiency |matters much more when transmitting than it does when receiving. It also does not follow that a lousy receiving antenna is good enough. For example, I *always* got better moon echos on 2-meter EME using the same antenna for transmit and receive. When I tried a wet string on receive I didn't hear nuthin' g I have observed the same on 20 meters. My Yagi at a modest height of 50 feet is *always* better than an indoor wire. | |Franks's observations are correct, and can be verified if you do a |detailed signal to noise calculation. You could also try the experiment |yourself. Two experiments cited above. |
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