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I sure disagree about being able to determine an antenna's efficiency by either resistance measurements or by measuring received signa;l strength at any one point in space. From practical, engineer's point of view, and we are looking at shortened (loaded) antennas, you (or at least I) want to know how efficient the loaded antenna is vs. equivalent (same pattern producing) antenna. You want to compare oranges with oranges. The ultimate indicator is how much is one better (worst) than the other producing more (less) transmit (or receive) signal. That is the ultimate parameter that we are looking for, that's what you want to measure and compare. We have dB as a unit for that. 3dB means you gain (lose) double (power) signal. If you lose 50% in the heat, you will see corresponding loss in signal strength. So forget the igloo! But, you are certainly a much smarter fuy than I ever was. So, I am not equipped to get into a news group contest. How did you arrive at that without putting me in the styrofoam igloo, or that I am Fuy? :-) It is my contention that the antenna under test's complete radiation pattern and field strength would have to be measured and integrated if field strength is used to determine it's efficiency. That could get coplicated. NOT! That's why you want to use the same pattern producing antennas for comparison (apples to apples) i.e. quarter wave (electrical) shortened (loaded) vertical vs. full size quarter wave vertical made of same material (tubing). You can make measurements at the same point (properly chosen) and compare signal levels while swapping the antennas at the same test site. It would have seemed to me that the loss in any "R" is dependent on the current flowing in it. And, I'd be concerned that any resonances could have higher circulating currents at the operating frequency. Circulating in what? If you can point out the errors in my convictions, I'd like to read about where I'm wrong. You can be "convicted" in anything you like. But you have to look at the problems and see what are you trying to achieve. I always try to make antenna to produce the maximum signal in the desired direction, pattern. That's what you try to measure, evaluate. Anything else is just contributing factor that gets included in the final parameter - signal strength. You can fart with heat, resistances, etc., I do not use antennas for heating, I use them for producing or extracting signals and that's what I am interested in and want to quantify. You need proper "standard" and use proper parameters to compare your "miracle" against. If Mr. Vincent "discovers" that his shortened antenna is more broadband than full size (same electrical length) radiator, than he has some serious resistors "broadening" the response. My dummy load is perfect broadband "antenna" and almost 100% "efficient" - turns almost 100% of power into a heat, but radiates almost nothing. The point is, you can measure other things like heat generated by the loses, but you are neglecting other parameters that come to play, leading you astray, while neglecting the most important parameter - the result you are (or I am) after - the signal strength! Does that "convict" you? Otherwise I rest my case. Jerry Yuri, K3BU.us |
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