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#1
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SWR read to TX or rather to the antenna ?
Hi,
It seems well-known that the SWR value that you read on an external meter or an antenna tuner is NOT the value measured between itself and the antenna. The SWR value "picked-up" and that you can change is the one measured between this meter or tuner and the transceiver (or the linear amplifier but we consider it as a black box if you use it properly). But recently I experimented the burning of my PL due to a high SWR, thus high current, and moisture and the end of the line (really, see image of PL's here http://www.astrosurf.com/lombry/qsl-...sion-line2.htm, end of page ). The distance between my RTX and SWR reader is short, about 1 m. But there are about 15m between the SWR and the feed point of my antenna where I had the problem. So I would like to know if an SWR meter does only read the value upstream or if the properties of the feedline to the antenna does not influence is reading. At first sight it does as during this problem I had a SWR 4:1 on the external SWR-meter. This value didn't come from the RTX side which built-in SWR displayed a VSWR 1:1. It really came from the other side, to the antenna, thus contrary to what I think and what is usually stated about the functioning of this device... Can someone explain me this ? Thanks in advance Thierry ON4SKY |
#2
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It seems well-known that the SWR value that you read on an external meter
or an antenna tuner is NOT the value measured between itself and the antenna. The SWR value "picked-up" and that you can change is the one measured between this meter or tuner and the transceiver (or the linear amplifier but we consider it as a black box if you use it properly). But recently I experimented the burning of my PL due to a high SWR, thus high current, and moisture and the end of the line (really, see image of PL's here http://www.astrosurf.com/lombry/qsl-...sion-line2.htm, end of page ). The distance between my RTX and SWR reader is short, about 1 m. But there are about 15m between the SWR and the feed point of my antenna where I had the problem. So I would like to know if an SWR meter does only read the value upstream or if the properties of the feedline to the antenna does not influence is reading. The SWR meter indicates the value from the meter to whatever is after it. If you insert a device that has a high SWR (because it becomes defective or for some other reason ) between the transmitter and SWR meter ( say a switch or filter), the meter can show a low value if the antenna is ok, but the transmitter will see a high SWR and may burn out the finals. |
#3
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The SWR meter indicates the value from the meter to whatever is after it.
If you insert a device that has a high SWR (because it becomes defective or for some other reason ) between the transmitter and SWR meter ( say a switch or filter), the meter can show a low value if the antenna is ok, but the transmitter will see a high SWR and may burn out the finals. He did not say he inserted anything, just that moisture at the end of his transmission line caused a fault. If this was the case, an SWR bridge at the output of his Power Amps should have alerted him to a problem that would potentially destroyed them. If you want to use an SWR bridge as a protective device, or indicator, it must be placed in the proper position in the antenna system. Modern transceivers have circuits that detect mismatches and reduce power to minimize failed output devices. 73 Gary N4AST |
#4
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Someone sed:
"...the meter can show a low value if the antenna is ok, but the transmitter will see a high SWR and may burn out the finals." ================ It's funny that this old wive's tale about the high SWR "burning out the finals" still exists. I guess it depends on what the meaning of "high" is. 73, Jack, K9CUN |
#5
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JDer8745 wrote:
It's funny that this old wive's tale about the high SWR "burning out the finals" still exists. I guess it depends on what the meaning of "high" is. If high SWR and the attendant mismatch cannot burn out a final, I wonder why most commercial finals are protected from a high SWR by foldback circuitry to avoid damage to the finals? -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
#6
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I wonder why most commercial finals are protected from a high SWR
by foldback circuitry to avoid damage to the finals? -- 73, Cecil ========================== They don't. There isn't an SWR meter on the station. They are really protecting the finals against excessive deflection of the TLI. ( Transmitter Loading Indicator.) But it sure makes a good point of conversation amongst the old wives. ---- Reg, G4FGQ |
#7
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"JGBOYLES" wrote in message ... The SWR meter indicates the value from the meter to whatever is after it. If you insert a device that has a high SWR (because it becomes defective or for some other reason ) between the transmitter and SWR meter ( say a switch or filter), the meter can show a low value if the antenna is ok, but the transmitter will see a high SWR and may burn out the finals. He did not say he inserted anything, just that moisture at the end of his transmission line caused a fault. If this was the case, an SWR bridge at the output of his Power Amps should have alerted him to a problem that would potentially destroyed them. If you want to use an SWR bridge as a protective device, or indicator, it must be placed in the proper position in the antenna system. Modern transceivers have circuits that detect mismatches and reduce power to minimize failed output devices. Indeed. A good suggestion I could install (in case of) Thierry 73 Gary N4AST |
#8
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"Cecil Moore" wrote in message ... JDer8745 wrote: It's funny that this old wive's tale about the high SWR "burning out the finals" still exists. I guess it depends on what the meaning of "high" is. If high SWR and the attendant mismatch cannot burn out a final, I wonder why most commercial finals are protected from a high SWR by foldback circuitry to avoid damage to the finals? Indeed. I always hear and read that a high SWR can destroy the PA final of TX, cranck coils, etc. Thierry -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
#9
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"JGBOYLES" wrote in message ... The SWR meter indicates the value from the meter to whatever is after it. If you insert a device that has a high SWR (because it becomes defective or for some other reason ) between the transmitter and SWR meter ( say a switch or filter), the meter can show a low value if the antenna is ok, but the transmitter will see a high SWR and may burn out the finals. He did not say he inserted anything, just that moisture at the end of his transmission line caused a fault. If this was the case, an SWR bridge at the The install was : RTX +50 cm RG58 + AMP + 1m Aircom (like RG213) + SWR +15m Aircom + G5RV the built-in SWR of my RTX TS-570D read SWR 1:1. If my external SWR displayed an SWR 4 that means that it read the info AFTER it, what looks in contradiction with what ARRL website states in his technical columns... Who's right ? Thierry ON4SKY http://www.astrosurf.com/lombry/ output of his Power Amps should have alerted him to a problem that would potentially destroyed them. If you want to use an SWR bridge as a protective device, or indicator, it must be placed in the proper position in the antenna system. Modern transceivers have circuits that detect mismatches and reduce power to minimize failed output devices. 73 Gary N4AST |
#10
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Reg Edwards wrote:
I wonder why most commercial finals are protected from a high SWR by foldback circuitry to avoid damage to the finals? They don't. There isn't an SWR meter on the station. Reg, I'm talking about commercially manufactured ham radio finals. Virtually every single one of them has protection circuitry and virtually every one of them has a built-in SWR metering system. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
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