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#1
July 6th 15, 12:52 AM
posted to rec.radio.amateur.antenna
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An antenna question--43 ft vertical
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#3
July 6th 15, 03:19 AM
posted to rec.radio.amateur.antenna
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An antenna question--43 ft vertical
On 7/5/2015 7:21 PM, wrote:
John S wrote: On 7/5/2015 5:24 PM, wrote: Roger Hayter wrote: wrote: The output impedance of an amateur transmitter IS approximately 50 Ohms as is trivially shown by reading the specifications for the transmitter which was designed and manufactured to match a 50 Ohm load. Do you think all those manuals are lies? You are starting with a false premise which makes everything after that false. A quick google demonstrates dozens of specification sheets that say the transmitter is designed for a 50 ohm load, and none that mention its output impedance. If the source impedance were other than 50 Ohms, the SWR with 50 Ohm coax and a 50 Ohm antenna would be high. It is not. Where is the source impedance found on a Smith chart? Also, if you have EZNEC, you will not find a place to specify source impedance but it will show the SWR. A Smith chart is normalized to 1. So, it can't be used in a 50 ohm environment? What does that have to do with anything? The chart has a SWR graph and nowhere does it need source impedance. If you disagree, please link to one. EZNEC allows you to set the impedance to anything you want and assumes the transmission line matches the transmitter. Please show the EZNEC statement that "assumes the transmission line matches the transmitter". Look in the help section if you have EZNEC and can cut and paste or just refer me to the chapter and verse. Also, if you have EZNEC, you can insert a transmission line with arbitrary characteristic impedance, put a load on the far end matching the line, and look at the SWR. It will still be 1:1 because the LOAD matches the LINE. Not because EZNEC assumes a source impedance. Try it with and report back here. There is no way that a source initiates reflections. That is a property of the line and load only. It may re-reflect a wave reflected from the load, but that is all. You can also verify this in LTSPICE if you wish. |
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#4
July 6th 15, 06:19 AM
posted to rec.radio.amateur.antenna
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An antenna question--43 ft vertical
John S wrote:
On 7/5/2015 7:21 PM, wrote: John S wrote: On 7/5/2015 5:24 PM, wrote: Roger Hayter wrote: wrote: The output impedance of an amateur transmitter IS approximately 50 Ohms as is trivially shown by reading the specifications for the transmitter which was designed and manufactured to match a 50 Ohm load. Do you think all those manuals are lies? You are starting with a false premise which makes everything after that false. A quick google demonstrates dozens of specification sheets that say the transmitter is designed for a 50 ohm load, and none that mention its output impedance. If the source impedance were other than 50 Ohms, the SWR with 50 Ohm coax and a 50 Ohm antenna would be high. It is not. Where is the source impedance found on a Smith chart? Also, if you have EZNEC, you will not find a place to specify source impedance but it will show the SWR. A Smith chart is normalized to 1. So, it can't be used in a 50 ohm environment? What does that have to do with anything? The chart has a SWR graph and nowhere does it need source impedance. If you disagree, please link to one. EZNEC allows you to set the impedance to anything you want and assumes the transmission line matches the transmitter. Please show the EZNEC statement that "assumes the transmission line matches the transmitter". Look in the help section if you have EZNEC and can cut and paste or just refer me to the chapter and verse. Also, if you have EZNEC, you can insert a transmission line with arbitrary characteristic impedance, put a load on the far end matching the line, and look at the SWR. It will still be 1:1 because the LOAD matches the LINE. Not because EZNEC assumes a source impedance. Try it with and report back here. There is no way that a source initiates reflections. That is a property of the line and load only. It may re-reflect a wave reflected from the load, but that is all. You can also verify this in LTSPICE if you wish. What happens if you take any off the shelf commercial amateur radio transmitter that does not have a built in tuner and: Attach a 10 Ohm load. Attach a 200 Ohm load. Attach a 1,000 Ohm load. Attach a 1 Ohm load. Attach a 50 Ohm load. -- Jim Pennino |
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#5
July 6th 15, 03:23 PM
posted to rec.radio.amateur.antenna
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An antenna question--43 ft vertical
On 7/6/2015 12:19 AM, wrote:
John S wrote: On 7/5/2015 7:21 PM, wrote: John S wrote: On 7/5/2015 5:24 PM, wrote: Roger Hayter wrote: wrote: The output impedance of an amateur transmitter IS approximately 50 Ohms as is trivially shown by reading the specifications for the transmitter which was designed and manufactured to match a 50 Ohm load. Do you think all those manuals are lies? You are starting with a false premise which makes everything after that false. A quick google demonstrates dozens of specification sheets that say the transmitter is designed for a 50 ohm load, and none that mention its output impedance. If the source impedance were other than 50 Ohms, the SWR with 50 Ohm coax and a 50 Ohm antenna would be high. It is not. Where is the source impedance found on a Smith chart? Also, if you have EZNEC, you will not find a place to specify source impedance but it will show the SWR. A Smith chart is normalized to 1. So, it can't be used in a 50 ohm environment? What does that have to do with anything? The chart has a SWR graph and nowhere does it need source impedance. If you disagree, please link to one. EZNEC allows you to set the impedance to anything you want and assumes the transmission line matches the transmitter. Please show the EZNEC statement that "assumes the transmission line matches the transmitter". Look in the help section if you have EZNEC and can cut and paste or just refer me to the chapter and verse. Also, if you have EZNEC, you can insert a transmission line with arbitrary characteristic impedance, put a load on the far end matching the line, and look at the SWR. It will still be 1:1 because the LOAD matches the LINE. Not because EZNEC assumes a source impedance. Try it with and report back here. There is no way that a source initiates reflections. That is a property of the line and load only. It may re-reflect a wave reflected from the load, but that is all. You can also verify this in LTSPICE if you wish. What happens if you take any off the shelf commercial amateur radio transmitter that does not have a built in tuner and: Attach a 10 Ohm load. Attach a 200 Ohm load. Attach a 1,000 Ohm load. Attach a 1 Ohm load. Attach a 50 Ohm load. Please address my questions first before setting up another strawman. |
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#6
July 6th 15, 05:48 PM
posted to rec.radio.amateur.antenna
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An antenna question--43 ft vertical
John S wrote:
On 7/6/2015 12:19 AM, wrote: John S wrote: On 7/5/2015 7:21 PM, wrote: John S wrote: On 7/5/2015 5:24 PM, wrote: Roger Hayter wrote: wrote: The output impedance of an amateur transmitter IS approximately 50 Ohms as is trivially shown by reading the specifications for the transmitter which was designed and manufactured to match a 50 Ohm load. Do you think all those manuals are lies? You are starting with a false premise which makes everything after that false. A quick google demonstrates dozens of specification sheets that say the transmitter is designed for a 50 ohm load, and none that mention its output impedance. If the source impedance were other than 50 Ohms, the SWR with 50 Ohm coax and a 50 Ohm antenna would be high. It is not. Where is the source impedance found on a Smith chart? Also, if you have EZNEC, you will not find a place to specify source impedance but it will show the SWR. A Smith chart is normalized to 1. So, it can't be used in a 50 ohm environment? What does that have to do with anything? The chart has a SWR graph and nowhere does it need source impedance. If you disagree, please link to one. EZNEC allows you to set the impedance to anything you want and assumes the transmission line matches the transmitter. Please show the EZNEC statement that "assumes the transmission line matches the transmitter". Look in the help section if you have EZNEC and can cut and paste or just refer me to the chapter and verse. Also, if you have EZNEC, you can insert a transmission line with arbitrary characteristic impedance, put a load on the far end matching the line, and look at the SWR. It will still be 1:1 because the LOAD matches the LINE. Not because EZNEC assumes a source impedance. Try it with and report back here. There is no way that a source initiates reflections. That is a property of the line and load only. It may re-reflect a wave reflected from the load, but that is all. You can also verify this in LTSPICE if you wish. What happens if you take any off the shelf commercial amateur radio transmitter that does not have a built in tuner and: Attach a 10 Ohm load. Attach a 200 Ohm load. Attach a 1,000 Ohm load. Attach a 1 Ohm load. Attach a 50 Ohm load. Please address my questions first before setting up another strawman. Start with Electromagnetics by Kraus and Carver, Chapter 13. -- Jim Pennino |
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#7
July 7th 15, 03:20 PM
posted to rec.radio.amateur.antenna
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An antenna question--43 ft vertical
On 06/07/15 17:48, wrote:
John S wrote: On 7/6/2015 12:19 AM, wrote: John S wrote: On 7/5/2015 7:21 PM, wrote: John S wrote: On 7/5/2015 5:24 PM, wrote: Roger Hayter wrote: wrote: The output impedance of an amateur transmitter IS approximately 50 Ohms as is trivially shown by reading the specifications for the transmitter which was designed and manufactured to match a 50 Ohm load. Do you think all those manuals are lies? You are starting with a false premise which makes everything after that false. A quick google demonstrates dozens of specification sheets that say the transmitter is designed for a 50 ohm load, and none that mention its output impedance. If the source impedance were other than 50 Ohms, the SWR with 50 Ohm coax and a 50 Ohm antenna would be high. It is not. Where is the source impedance found on a Smith chart? Also, if you have EZNEC, you will not find a place to specify source impedance but it will show the SWR. A Smith chart is normalized to 1. So, it can't be used in a 50 ohm environment? What does that have to do with anything? The chart has a SWR graph and nowhere does it need source impedance. If you disagree, please link to one. EZNEC allows you to set the impedance to anything you want and assumes the transmission line matches the transmitter. Please show the EZNEC statement that "assumes the transmission line matches the transmitter". Look in the help section if you have EZNEC and can cut and paste or just refer me to the chapter and verse. Also, if you have EZNEC, you can insert a transmission line with arbitrary characteristic impedance, put a load on the far end matching the line, and look at the SWR. It will still be 1:1 because the LOAD matches the LINE. Not because EZNEC assumes a source impedance. Try it with and report back here. There is no way that a source initiates reflections. That is a property of the line and load only. It may re-reflect a wave reflected from the load, but that is all. You can also verify this in LTSPICE if you wish. What happens if you take any off the shelf commercial amateur radio transmitter that does not have a built in tuner and: Attach a 10 Ohm load. Attach a 200 Ohm load. Attach a 1,000 Ohm load. Attach a 1 Ohm load. Attach a 50 Ohm load. Please address my questions first before setting up another strawman. Start with Electromagnetics by Kraus and Carver, Chapter 13. Do the experiment. |
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#8
July 7th 15, 03:14 PM
posted to rec.radio.amateur.antenna
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An antenna question--43 ft vertical
On 06/07/15 01:21, wrote:
John S wrote: On 7/5/2015 5:24 PM, wrote: Roger Hayter wrote: wrote: The output impedance of an amateur transmitter IS approximately 50 Ohms as is trivially shown by reading the specifications for the transmitter which was designed and manufactured to match a 50 Ohm load. Do you think all those manuals are lies? You are starting with a false premise which makes everything after that false. A quick google demonstrates dozens of specification sheets that say the transmitter is designed for a 50 ohm load, and none that mention its output impedance. If the source impedance were other than 50 Ohms, the SWR with 50 Ohm coax and a 50 Ohm antenna would be high. It is not. Where is the source impedance found on a Smith chart? Also, if you have EZNEC, you will not find a place to specify source impedance but it will show the SWR. A Smith chart is normalized to 1. That is true but is doesn't address the point. There should still be somewhere to represent the source impedance, albeit normalised. EZNEC allows you to set the impedance to anything you want and assumes the transmission line matches the transmitter. Likewise, that is a sweeping statement which evades the point. |
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#9
July 7th 15, 07:56 PM
posted to rec.radio.amateur.antenna
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An antenna question--43 ft vertical
Brian Reay wrote:
On 06/07/15 01:21, wrote: John S wrote: On 7/5/2015 5:24 PM, wrote: Roger Hayter wrote: wrote: The output impedance of an amateur transmitter IS approximately 50 Ohms as is trivially shown by reading the specifications for the transmitter which was designed and manufactured to match a 50 Ohm load. Do you think all those manuals are lies? You are starting with a false premise which makes everything after that false. A quick google demonstrates dozens of specification sheets that say the transmitter is designed for a 50 ohm load, and none that mention its output impedance. If the source impedance were other than 50 Ohms, the SWR with 50 Ohm coax and a 50 Ohm antenna would be high. It is not. Where is the source impedance found on a Smith chart? Also, if you have EZNEC, you will not find a place to specify source impedance but it will show the SWR. A Smith chart is normalized to 1. That is true but is doesn't address the point. There should still be somewhere to represent the source impedance, albeit normalised. The purpose of a Smith chart it to match a SOURCE to a LOAD. EZNEC allows you to set the impedance to anything you want and assumes the transmission line matches the transmitter. Likewise, that is a sweeping statement which evades the point. The main purpose of EZNEC is to design an antenna for amateur radio use and all commercial amateur radio transmitters have an output impedance of 50 Ohms. -- Jim Pennino |
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#10
July 8th 15, 07:36 PM
posted to rec.radio.amateur.antenna
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An antenna question--43 ft vertical
Brian Reay wrote:
wrote: Brian Reay wrote: On 06/07/15 01:21, wrote: John S wrote: On 7/5/2015 5:24 PM, wrote: Roger Hayter wrote: wrote: The output impedance of an amateur transmitter IS approximately 50 Ohms as is trivially shown by reading the specifications for the transmitter which was designed and manufactured to match a 50 Ohm load. Do you think all those manuals are lies? You are starting with a false premise which makes everything after that false. A quick google demonstrates dozens of specification sheets that say the transmitter is designed for a 50 ohm load, and none that mention its output impedance. If the source impedance were other than 50 Ohms, the SWR with 50 Ohm coax and a 50 Ohm antenna would be high. It is not. Where is the source impedance found on a Smith chart? Also, if you have EZNEC, you will not find a place to specify source impedance but it will show the SWR. A Smith chart is normalized to 1. That is true but is doesn't address the point. There should still be somewhere to represent the source impedance, albeit normalised. The purpose of a Smith chart it to match a SOURCE to a LOAD. EZNEC allows you to set the impedance to anything you want and assumes the transmission line matches the transmitter. Likewise, that is a sweeping statement which evades the point. The main purpose of EZNEC is to design an antenna for amateur radio use and all commercial amateur radio transmitters have an output impedance of 50 Ohms. Neither of those responses address the points. It is clear you cannot support your assertions. EZNEC can set the source impedance to any value one desires, but the default is 50 Ohms as most people are interested in 50 Ohm systems as the majority of transmitters are designed for 50 Ohm loads. EZNEC calculates the SWR for an antenna presented to the SOURCE in the model. For most simulations, the SOURCE is placed at the antenna terminals, which represents what an attached transmission line will see. The transmission line most commonly used is 50 Ohm coax. EZNEC will also allow you to put a SOURCE at one end of a transmission line with the other end of the line at the antenna terminals. In this simulation, EZNEC simulates what the transmitter would see if it were connected to the transmission line/antenna system. SWR is defined in terms of SOURCE impedance and LOAD impedance. SWR = (1 + |r|)/(1 - |r|) Where r = reflection coefficient and r = (Zl - Zo)/(Zl + Zo) Where Zl = complex load impedance, Zo = complex source impedance. -- Jim Pennino |
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