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An antenna question--43 ft vertical
On 6/30/2015 12:40 PM, Tom W3TDH wrote:
I know that what I am about to say is provocative to some but I still think it is worth saying. If you look at the way that commercial and military radios are matched to antennas you will notice that most of the matching is done as close to the feed point as practical. Since only the power that actually reaches the antenna can be radiated I have a hard time seeing the point of matching the transmitter to the feed line. Matching at the feed line connection point will prevent damage to the transmitter but if that were the main objective a dummy load would accomplish that. When you couple the antenna to the load at the feed point you can have extremely low losses in the feed line. When you do the matching at the feed point you will transfer the most energy possible to the antenna and will get the highest available effective radiated power. Since the objective is the transfer of the highest practical amount of power to the antenna the place to do that is at the feed point were possible. I do realize that it is often simpler and easier to match at the feed line connection but I felt obliged to point out that is is not the most effective place to do the job. Has it occurred to you that it might be important to match impedance both at the transmitter and at the antenna? When the feed line is not impedance matched to the transmitter output the maximum power is not transferred into the feed line. Then you have already lost power that can't be recovered by the matching at the antenna even if it is perfect. Your statements are not really provocative, they are just incomplete and/or wrong. -- Rick |
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An antenna question--43 ft vertical
On Tuesday, June 30, 2015 at 2:36:51 PM UTC-4, rickman wrote:
On 6/30/2015 12:40 PM, Tom W3TDH wrote: I know that what I am about to say is provocative to some but I still think it is worth saying. If you look at the way that commercial and military radios are matched to antennas you will notice that most of the matching is done as close to the feed point as practical. Since only the power that actually reaches the antenna can be radiated I have a hard time seeing the point of matching the transmitter to the feed line. Matching at the feed line connection point will prevent damage to the transmitter but if that were the main objective a dummy load would accomplish that. When you couple the antenna to the load at the feed point you can have extremely low losses in the feed line. When you do the matching at the feed point you will transfer the most energy possible to the antenna and will get the highest available effective radiated power. Since the objective is the transfer of the highest practical amount of power to the antenna the place to do that is at the feed point were possible. I do realize that it is often simpler and easier to match at the feed line connection but I felt obliged to point out that is is not the most effective place to do the job. Has it occurred to you that it might be important to match impedance both at the transmitter and at the antenna? When the feed line is not impedance matched to the transmitter output the maximum power is not transferred into the feed line. Then you have already lost power that can't be recovered by the matching at the antenna even if it is perfect. Your statements are not really provocative, they are just incomplete and/or wrong. -- Rick Rick OK I'll buy incomplete and therefore wrong. Now given a Fifty Ohm feed line connected to a transmitter that is designed for that impedance at the antenna connector does not the actual mismatch occur at the antenna feed point? Certainly that can be compensated for at the transmitter but isn't there a likelihood or at least a risk that you will loose significant effective radiated power in spite of adjusting the apparent feed line impedance to the transmitter? If I do the matching at the feed point will I not maximize the effective radiated power of the antenna by installing the tuner at the feed point. I have already conceded that it is not as convenient to do the matching at the feed point. I do not allege that doing the matching at the transmitter end of the feed line is inherently ineffective only that there is a greater likelihood of loosing ERP needlessly and invisibly if the matching is done at transmitter end of the feed line. By this I mean to ask if I may well deceive the power meeter into showing more power out then I am actually getting. If any power lost is very likely to be insignificant at a practical level than help me to understand why that would be true and I will sell off my Icon AH-4, together with the control converter that allows my Yaesu FT-857D to control it, and my SGC SG-235 and go back to using the Yaesu FC-30 tuner with my FT-857D and the built in tuner on my Yaesu FT-1000. This is especially important for me to get right with my FT-857D since it is the transceiver that I use for my personal go kit. If putting the Icon AH-4 on the mast and running the control line in addition to the coaxial cable is a waste of time I would really appreciate knowing that. Thank you for helping with my education on this issue. -- Tom Horne W3TDH |
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An antenna question--43 ft vertical
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An antenna question--43 ft vertical
Wayne wrote:
snip In my own particular case, an automatic remotely tuned ATU would be a pain to install/maintain. This part I do not understand at all. At the antenna end is a box with a connector for the feed line and a connector for the antenna. There is nothing to maintain there. If you get an ATU that gets it's power through the coax, you put the power injector in line with the feed line in the shack. There is nothing to maintain there either and you do not need to run any extra wires out to the antenna. -- Jim Pennino |
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An antenna question--43 ft vertical
wrote in message ... Wayne wrote: snip In my own particular case, an automatic remotely tuned ATU would be a pain to install/maintain. This part I do not understand at all. At the antenna end is a box with a connector for the feed line and a connector for the antenna. There is nothing to maintain there. If you get an ATU that gets it's power through the coax, you put the power injector in line with the feed line in the shack. There is nothing to maintain there either and you do not need to run any extra wires out to the antenna. The problem is with my own particular case. The antenna is a whip mounted in the middle of a metal roof. At my age, I shouldn't be wandering around on or climbing such a roof. Once installed, any failure would require a trip to the roof. The ATU would be exposed to extreme temperature and sunlight that might eventually induce failures. |
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An antenna question--43 ft vertical
Wayne wrote:
wrote in message ... Wayne wrote: snip In my own particular case, an automatic remotely tuned ATU would be a pain to install/maintain. This part I do not understand at all. At the antenna end is a box with a connector for the feed line and a connector for the antenna. There is nothing to maintain there. If you get an ATU that gets it's power through the coax, you put the power injector in line with the feed line in the shack. There is nothing to maintain there either and you do not need to run any extra wires out to the antenna. The problem is with my own particular case. The antenna is a whip mounted in the middle of a metal roof. At my age, I shouldn't be wandering around on or climbing such a roof. Once installed, any failure would require a trip to the roof. The ATU would be exposed to extreme temperature and sunlight that might eventually induce failures. The age part I can understand; an inverted, cheap plastic trash can will provide more than adequate protection against the elements. -- Jim Pennino |
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An antenna question--43 ft vertical
On 7/2/2015 3:17 PM, Wayne wrote:
wrote in message ... Wayne wrote: snip In my own particular case, an automatic remotely tuned ATU would be a pain to install/maintain. This part I do not understand at all. At the antenna end is a box with a connector for the feed line and a connector for the antenna. There is nothing to maintain there. If you get an ATU that gets it's power through the coax, you put the power injector in line with the feed line in the shack. There is nothing to maintain there either and you do not need to run any extra wires out to the antenna. The problem is with my own particular case. The antenna is a whip mounted in the middle of a metal roof. At my age, I shouldn't be wandering around on or climbing such a roof. Once installed, any failure would require a trip to the roof. The ATU would be exposed to extreme temperature and sunlight that might eventually induce failures. A friend of mine who is past 70 has had a TV antenna preamp on his roof for some 50 years. He has been up there to check it at least once when he couldn't get the digital TV signals as well any more. It was not the problem. If a unit is constructed well, it should live a rich, full life on the roof, protected from the abuse it might receive in your shack. -- Rick |
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