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Cecil Moore wrote: Cecil Moore wrote: wrote: It was stipulated in the original post that the swr was being measured at the source end for the 50 ohm line. If all one changes is the impedance of a 1/2 electrical wavelength line, and nothing else, the answer is 1:1. Nope, not if a 72 ohm SWR meter is being used. An SWR meter calibrated for the transmission line Z0 of 72 ohms will read 1.44:1 even if the 50 ohm transmitter is happy with the 50+j0 ohm virtual impedance being presented to it. I have SWR meters calibrated for 50, 75, 300, 450, and 600 ohms - doesn't everybody? Please note that it was ***NOT*** stipulated in the original post that the SWR meter was calibrated for 50 ohms. "What is the SWR?" was the question. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- SWR meter reads 1:1 at the source with 50 ohm line, that will tell you that the swr bridge Z and the antenna Z are the same initially (1/2 wave line). Changing to 72 ohm line will still be 1:1. Gary N4AST |
wrote:
SWR meter reads 1:1 at the source with 50 ohm line, that will tell you that the swr bridge Z and the antenna Z are the same initially (1/2 wave line). Changing to 72 ohm line will still be 1:1. Here is the original question again: "What would the SWR be if I substituted the 50 Ohm feedline with a 1/2 wavelength of 72 Ohm feedline?" Did he ask what would a 50 ohm SWR meter read? NO! He asked "WHAT WOULD THE SWR BE ..." The SWR would be 72/50=1.44:1 on the 72 ohm feedline. That answers the original question. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
It was stipulated in the original post that the swr was being
measured at the source end for the 50 ohm line. He said, "WHAT WOULD THE SWR BE ...?" not what would a 50 ohm SWR meter measure. The SWR would be 1.44:1 on the 72 ohm feedline no matter what the 50 ohm SWR meter erroneously measured. If all one changes is the impedance of a 1/2 electrical wavelength line, and nothing else, the answer is 1:1. Did not say anything about measuring the swr anywhere but at the source. Go back and read the question again, Tom. He asked: "What would the SWR be if I substituted the 50 Ohm feedline with a 1/2 wavelength of 72 Ohm feedline?" Did he say, "What SWR would be measured?" NO!!! Did he say, "What would the SWR be ...?" YES!!! ***THE SWR WOULD BE 1.44:1*** on the 72 ohm feedline. You guys are not answering the question that he asked. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
Reg Edwards wrote:
You will be pleased to hear I'm back on Sierra Valley, Californian Red tonight. Peter Vella Merlot for me. My doctor told me to drink two glasses of red wine a day so I use ~400 ml iced-tea glasses. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
Tom Donaly wrote:
VSWR stands for Voltage Standing Wave Ratio. It's supposed to be the ratio of the greatest voltage on a transmission line to the least voltage on the same line. On the line with a 72 ohm Z0, and a 50 ohm load, there exists a standing wave, and the ratio of maximum to minimum is 1.44 whether you measure it with a 50 ohm bridge at the beginning or not. If you define SWR as what a 50 ohm SWR bridge measures, you haven't quite grasped the concept. And Fred didn't ask what an SWR bridge would measure. He asked: "What would the SWR be ... ?" You're right. The SWR would be 1.44:1. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
Cecil Moore wrote:
Go back and read the question again, Tom. He asked: Sorry, Tom, somehow I screwed up the attributes. I don't think you posted what I responded to. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
OK CECIL!!!
Leave it up to you to pull the rug out from under me... If I have a transmitter that has 50 ohm out, and it is going to hook to a 50 ohm cable (and I can't see how this coax is terminated) why would I ever choose anything other than a 50 ohm calibrated swr meter to measure it with? Is that what I have seen on FS meters before (a rise in apparent radiation from the coax shield--and yet match looks good) and the 1/2 wave coax is really now part of the antenna? And, if the meter didn't give me the right reading, and cooked my "BEEG LEENEAIR" could I sue the manufacturer, buy a yacht and live in the Bahamas, drinking Peter Vella Merlot? grin Warmest regards, John "Cecil Moore" wrote in message ... Tom Donaly wrote: VSWR stands for Voltage Standing Wave Ratio. It's supposed to be the ratio of the greatest voltage on a transmission line to the least voltage on the same line. On the line with a 72 ohm Z0, and a 50 ohm load, there exists a standing wave, and the ratio of maximum to minimum is 1.44 whether you measure it with a 50 ohm bridge at the beginning or not. If you define SWR as what a 50 ohm SWR bridge measures, you haven't quite grasped the concept. And Fred didn't ask what an SWR bridge would measure. He asked: "What would the SWR be ... ?" You're right. The SWR would be 1.44:1. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
Cecil:
I screwed that up... in the above, should have been... "If I have a transmitter that has 50 ohm out, and it is going to hook to a 72 ohm cable..." The 72 ohm cable being t he only difference... and point being--don't I only care I am presenting a 50 ohm load to the transmitter? Warmest regards, John "John Smith" wrote in message ... OK CECIL!!! Leave it up to you to pull the rug out from under me... If I have a transmitter that has 50 ohm out, and it is going to hook to a 50 ohm cable (and I can't see how this coax is terminated) why would I ever choose anything other than a 50 ohm calibrated swr meter to measure it with? Is that what I have seen on FS meters before (a rise in apparent radiation from the coax shield--and yet match looks good) and the 1/2 wave coax is really now part of the antenna? And, if the meter didn't give me the right reading, and cooked my "BEEG LEENEAIR" could I sue the manufacturer, buy a yacht and live in the Bahamas, drinking Peter Vella Merlot? grin Warmest regards, John "Cecil Moore" wrote in message ... Tom Donaly wrote: VSWR stands for Voltage Standing Wave Ratio. It's supposed to be the ratio of the greatest voltage on a transmission line to the least voltage on the same line. On the line with a 72 ohm Z0, and a 50 ohm load, there exists a standing wave, and the ratio of maximum to minimum is 1.44 whether you measure it with a 50 ohm bridge at the beginning or not. If you define SWR as what a 50 ohm SWR bridge measures, you haven't quite grasped the concept. And Fred didn't ask what an SWR bridge would measure. He asked: "What would the SWR be ... ?" You're right. The SWR would be 1.44:1. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
John Smith wrote:
Leave it up to you to pull the rug out from under me... If I have a transmitter that has 50 ohm out, and it is going to hook to a 50 ohm cable (and I can't see how this coax is terminated) why would I ever choose anything other than a 50 ohm calibrated swr meter to measure it with? Some of us want to know what the SWR on the feedline is. That's how we calculate feedline losses. I get a kick out of some ham saying, "I'm running a 66' dipole on 75m and my SWR is 1.1:1." All that means is that the virtual impedance at the tuner input is probably 45 ohms or 55 ohms. But what is the SWR at the output of the tuner where it matters the most? -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
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