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#11
September 11th 15, 12:23 PM
posted to rec.radio.amateur.antenna
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The nature of Free Space (Once called, "The Lumeniferous Aether")
"Wayne" wrote in message
... Well, I don't know what you are calling "retarded potential". It is the term for the electric potential that must have existed on an antenna when analysing the radiated signal at some distant point. It is termed, "retarded" because the radiation originated at some time in the past. |
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#12
September 11th 15, 06:40 PM
posted to rec.radio.amateur.antenna
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The nature of Free Space (Once called, "The Lumeniferous Aether")
"gareth" wrote in message ... "Wayne" wrote in message ... Well, I don't know what you are calling "retarded potential". It is the term for the electric potential that must have existed on an antenna when analysing the radiated signal at some distant point. It is termed, "retarded" because the radiation originated at some time in the past. OK now I know. I hadn't heard the term before. But, how about my question? " if the radiated power is equal for two different antennas, why would the field strength be different, except as related to pattern differences?" The radiated power just is spread out differently. |
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#13
September 11th 15, 07:10 PM
posted to rec.radio.amateur.antenna
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The nature of Free Space (Once called, "The Lumeniferous Aether")
"Wayne" wrote in message
... "gareth" wrote in message ... "Wayne" wrote in message ... Well, I don't know what you are calling "retarded potential". It is the term for the electric potential that must have existed on an antenna when analysing the radiated signal at some distant point. It is termed, "retarded" because the radiation originated at some time in the past. OK now I know. I hadn't heard the term before. But, how about my question? " if the radiated power is equal for two different antennas, why would the field strength be different, except as related to pattern differences?" The radiated power just is spread out differently. Quoting from Electromagnetism by F.N.H.Robinson in the Oxfors Physic Series, 1973 edition ISBN 0 19 851806 4, Chapter 11, Radiation and page 100 .. The radiated power is proportional to the current times the antenna length divided by the wavelenght, and all squared. Therefore, to achieve the same radiated power from a short antenna, the current in the antenna has to be higher. HTH |
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#14
September 11th 15, 07:18 PM
posted to rec.radio.amateur.antenna
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The nature of Free Space (Once called, "The Lumeniferous Aether")
"gareth" wrote in message ... "Wayne" wrote in message ... "gareth" wrote in message ... "Wayne" wrote in message ... Well, I don't know what you are calling "retarded potential". It is the term for the electric potential that must have existed on an antenna when analysing the radiated signal at some distant point. It is termed, "retarded" because the radiation originated at some time in the past. OK now I know. I hadn't heard the term before. But, how about my question? " if the radiated power is equal for two different antennas, why would the field strength be different, except as related to pattern differences?" The radiated power just is spread out differently. Quoting from Electromagnetism by F.N.H.Robinson in the Oxfors Physic Series, 1973 edition ISBN 0 19 851806 4, Chapter 11, Radiation and page 100 .. The radiated power is proportional to the current times the antenna length divided by the wavelenght, and all squared. Therefore, to achieve the same radiated power from a short antenna, the current in the antenna has to be higher. But wasn't it implicit in your original statement that the power was equal in both the 1/4 wave and the shorter antenna? So for your assertion, we don't need to know the current. |
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#15
September 11th 15, 07:21 PM
posted to rec.radio.amateur.antenna
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The nature of Free Space (Once called, "The Lumeniferous Aether")
"Wayne" wrote in message
... "gareth" wrote in message ... "Wayne" wrote in message ... "gareth" wrote in message ... "Wayne" wrote in message ... Well, I don't know what you are calling "retarded potential". It is the term for the electric potential that must have existed on an antenna when analysing the radiated signal at some distant point. It is termed, "retarded" because the radiation originated at some time in the past. OK now I know. I hadn't heard the term before. But, how about my question? " if the radiated power is equal for two different antennas, why would the field strength be different, except as related to pattern differences?" The radiated power just is spread out differently. Quoting from Electromagnetism by F.N.H.Robinson in the Oxfors Physic Series, 1973 edition ISBN 0 19 851806 4, Chapter 11, Radiation and page 100 .. The radiated power is proportional to the current times the antenna length divided by the wavelenght, and all squared. Therefore, to achieve the same radiated power from a short antenna, the current in the antenna has to be higher. But wasn't it implicit in your original statement that the power was equal in both the 1/4 wave and the shorter antenna? No, for I was referring to the power arriving at some point in the far field |
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#16
September 11th 15, 07:22 PM
posted to rec.radio.amateur.antenna
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The nature of Free Space (Once called, "The Lumeniferous Aether")
On 9/11/2015 1:10 PM, gareth wrote:
"Wayne" wrote in message ... "gareth" wrote in message ... "Wayne" wrote in message ... Well, I don't know what you are calling "retarded potential". It is the term for the electric potential that must have existed on an antenna when analysing the radiated signal at some distant point. It is termed, "retarded" because the radiation originated at some time in the past. OK now I know. I hadn't heard the term before. But, how about my question? " if the radiated power is equal for two different antennas, why would the field strength be different, except as related to pattern differences?" The radiated power just is spread out differently. Quoting from Electromagnetism by F.N.H.Robinson in the Oxfors Physic Series, 1973 edition ISBN 0 19 851806 4, Chapter 11, Radiation and page 100 .. The radiated power is proportional to the current times the antenna length divided by the wavelenght, and all squared. Therefore, to achieve the same radiated power from a short antenna, the current in the antenna has to be higher. There is no contradiction there. Current is not power. Power is voltage times current. Since the impedance of a short antenna is not the same as the impedance of a larger antenna, it makes perfect sense that the current for a given power level will not be the same. -- Rick |
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#17
September 11th 15, 07:24 PM
posted to rec.radio.amateur.antenna
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The nature of Free Space (Once called, "The Lumeniferous Aether")
gareth wrote:
"Wayne" wrote in message ... "gareth" wrote in message ... "Wayne" wrote in message ... Well, I don't know what you are calling "retarded potential". It is the term for the electric potential that must have existed on an antenna when analysing the radiated signal at some distant point. It is termed, "retarded" because the radiation originated at some time in the past. OK now I know. I hadn't heard the term before. But, how about my question? " if the radiated power is equal for two different antennas, why would the field strength be different, except as related to pattern differences?" The radiated power just is spread out differently. Quoting from Electromagnetism by F.N.H.Robinson in the Oxfors Physic Series, 1973 edition ISBN 0 19 851806 4, Chapter 11, Radiation and page 100 .. The radiated power is proportional to the current times the antenna length divided by the wavelenght, and all squared. Therefore, to achieve the same radiated power from a short antenna, the current in the antenna has to be higher. HTH Congratulations, you have just confirmed Ohm's law. -- Jim Pennino |
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#18
September 11th 15, 07:35 PM
posted to rec.radio.amateur.antenna
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The nature of Free Space (Once called, "The Lumeniferous Aether")
wrote:
gareth wrote: "Wayne" wrote in message ... "gareth" wrote in message ... "Wayne" wrote in message ... Well, I don't know what you are calling "retarded potential". It is the term for the electric potential that must have existed on an antenna when analysing the radiated signal at some distant point. It is termed, "retarded" because the radiation originated at some time in the past. OK now I know. I hadn't heard the term before. But, how about my question? " if the radiated power is equal for two different antennas, why would the field strength be different, except as related to pattern differences?" The radiated power just is spread out differently. Quoting from Electromagnetism by F.N.H.Robinson in the Oxfors Physic Series, 1973 edition ISBN 0 19 851806 4, Chapter 11, Radiation and page 100 .. The radiated power is proportional to the current times the antenna length divided by the wavelenght, and all squared. Therefore, to achieve the same radiated power from a short antenna, the current in the antenna has to be higher. HTH Congratulations, you have just confirmed Ohm's law. Does he get a certificate or something to honour this milestone in radio science? -- STC // M0TEY // twitter.com/ukradioamateur |
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#19
September 11th 15, 07:48 PM
posted to rec.radio.amateur.antenna
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The nature of Free Space (Once called, "The Lumeniferous Aether")
"rickman" wrote in message
... There is no contradiction there. Current is not power. Power is voltage times current. Since the impedance of a short antenna is not the same as the impedance of a larger antenna, it makes perfect sense that the current for a given power level will not be the same. Feed 1kW into your 472kHz antenna and get only 1W erp, most of the high current driving the ohmic resistance and not the radiation resistance |
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#20
September 11th 15, 11:45 PM
posted to rec.radio.amateur.antenna
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The nature of Free Space (Once called, "The Lumeniferous Aether")
On 9/11/2015 1:48 PM, gareth wrote:
"rickman" wrote in message ... There is no contradiction there. Current is not power. Power is voltage times current. Since the impedance of a short antenna is not the same as the impedance of a larger antenna, it makes perfect sense that the current for a given power level will not be the same. Feed 1kW into your 472kHz antenna and get only 1W erp, most of the high current driving the ohmic resistance and not the radiation resistance You have had this discussion with many others here before. What is your point? Every antenna design has different losses depending on all the details of construction. So what? -- Rick |
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