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Jerry Martes wrote:
Roy Since I consider antenna efficiency difficult to measure accurately, I'd be willing to try to measure it as carefully as *practical*. If that required that the referance heater had a similar "thermal mass" to that of the antenna under test, I could probably make a heater that did have a thermal mass equivalent to that of the antenna. But, I would propose that there is no easier way to actually measure an antenna's efficiency than to measure the amount of power it turns into heat. Thats a statement I cant back up, and I know it. What is a better way to measure an antenna's efficiency?? I believe it would usually be easier and more accurate to measure the amount of power it turns into radiation. That is, measure the strength of the radiated field compared with an antenna of known efficiency and preferably having a similar pattern. Neither is easy, and a method that's "practical" from your point of view might well yield results which are so grossly inaccurate as to be useless. But go ahead, do a careful estimate of the accuracy you expect, do some measurements of various simple antennas whose loss is easy to calculate and compare the measured results, and see how well you can do. It's probably within the reach of a very careful amateur to make measurements which are accurate enough to be useful. It just isn't easy, and requires knowing the relationship between heat and temperature, where the heat is going, sources of error and the amount they can contribute, and a whole lot of care and attention to detail. And that's to get even crudely accurate results. For myself, I'd model it as Reg suggests (although I'd use a program rather than the back of an envelope as he would) and easily believe that the model results are more accurate than any measurement I'd be able to make. However, neither calculation or measurement results are likely to alter the claims made by manufacturers of miracle antennas and their fans. Roy Lewallen, W7EL |
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"Roy Lewallen" wrote in message ... Jerry Martes wrote: Roy Since I consider antenna efficiency difficult to measure accurately, I'd be willing to try to measure it as carefully as *practical*. If that required that the referance heater had a similar "thermal mass" to that of the antenna under test, I could probably make a heater that did have a thermal mass equivalent to that of the antenna. But, I would propose that there is no easier way to actually measure an antenna's efficiency than to measure the amount of power it turns into heat. Thats a statement I cant back up, and I know it. What is a better way to measure an antenna's efficiency?? I believe it would usually be easier and more accurate to measure the amount of power it turns into radiation. That is, measure the strength of the radiated field compared with an antenna of known efficiency and preferably having a similar pattern. Neither is easy, and a method that's "practical" from your point of view might well yield results which are so grossly inaccurate as to be useless. But go ahead, do a careful estimate of the accuracy you expect, do some measurements of various simple antennas whose loss is easy to calculate and compare the measured results, and see how well you can do. It's probably within the reach of a very careful amateur to make measurements which are accurate enough to be useful. It just isn't easy, and requires knowing the relationship between heat and temperature, where the heat is going, sources of error and the amount they can contribute, and a whole lot of care and attention to detail. And that's to get even crudely accurate results. For myself, I'd model it as Reg suggests (although I'd use a program rather than the back of an envelope as he would) and easily believe that the model results are more accurate than any measurement I'd be able to make. However, neither calculation or measurement results are likely to alter the claims made by manufacturers of miracle antennas and their fans. Roy Lewallen, W7EL Roy If I had your credentials, I'd measure antenna efficiency the way you prescribe. It is only because I have no faith in my abiliuty to convince anyone what the pattern of a "New-Revolutionary is, that I'd get a thermometer out to chech my predictions that the antenna has *no* loss, like this guy does. As I read this thread, there is one guy who thinks measuring the temperature of an antenna for getting information on its efficiency. And all the other posts consider that guy to be 'on the wrong path'. I'd advise doing it some way *other than* measuring heat of the antenna. Jerry |
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