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#1
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Max power into 26 ga. longwire?
What is the maximum power I can safely use on 160M and 80M on 26 ga.
copper-plated stranded steel wire? 200 watts? What is the minimum gauge for a longwire of this material if I want it to handle 600 watts? Ken KC2JDY Ken (to reply via email remove "zz" from address) |
#2
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Your question cannot be answered unless you specify the maximum allowable
temperature of the wire and whether your antenna is in northern Alaska in midwinter at midnight, or in New Mexico at midsummer at noon. But to be on the safe side, allow for a dissipation of 1 watt per foot length of dipole wire which will then get warm in the centre, somewhat above ambient, when in a slight breeze. So for a 130 foot, 160-meter dipole, allow 130 watts dissipation. This antenna will easily handle 1 kilowatt of Tx power at a typical efficiency of about 87 percent for copper-plated, stranded steel wire. ---- Reg, G4FGQ "Ken" wrote in message ... What is the maximum power I can safely use on 160M and 80M on 26 ga. copper-plated stranded steel wire? 200 watts? What is the minimum gauge for a longwire of this material if I want it to handle 600 watts? Ken KC2JDY Ken (to reply via email remove "zz" from address) |
#3
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But to be on the safe side, allow for a dissipation of 1 watt per foot
length of dipole wire which will then get warm in the centre, somewhat above ambient, when in a slight breeze. But the current distribution isn't linear, and the loss is I^2R, so I would think you'd have to know the max current, and work it that way. -- KC6ETE Dave's Engineering Page, www.dvanhorn.org Microcontroller Consultant, specializing in Atmel AVR |
#4
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"Dave VanHorn" wrote - Reg wrote - But to be on the safe side, allow for a dissipation of 1 watt per foot length of dipole wire which will then get warm in the centre, somewhat above ambient, when in a slight breeze. But the current distribution isn't linear, and the loss is I^2R, so I would think you'd have to know the max current, and work it that way. ============================ Yes Dave, I know. But I did say the wire gets warm at the centre. Sorry I forgot to say it remains cold at the ends except for the small conduction of heat along the wire. And it does not get quite so warm when it rains or snows. Actually, the current distribution along a 1/2-wave dipole is exactly a sinewaveform. This is arithmetically very convenient because the linearly distributed wire resistance then behaves as though it is lumped at the dipole centre with a value exactly half of the overall distributed value. Now the end-to-end resistance of a 1/2-wave, 160-meter dipole, made with 26-gauge copper-plated wire, is about 22 ohms. Therefore the feedpoint resistance of the antenna is the radiation resistance of 73 plus 22/2 ohms = 84 ohms. Therefore, with Tx power equal to 1000 watts and a current at the centre equal to 3.45 amps, the overall loss of power dissipated in the antenna wire is equal to 3.45 squared times half of the end-to-end conductor resistance of 11 ohms. Which (as I said in my previous message) equals 131 watts. Which raises the wire temperature a harmless handfull of a few degrees Celsius. Actual temperature, of course, depends on the open-air ambient temperature at noon, in June, in the New Mexico desert. Antenna radiating efficiency = 73/(73+11) = 84 percent, or a loss of 0.76 decibels, or 1/8th of an S-unit. Which, by no stretch of the imagination, is likely to influence the results of a contest. Isn't it remarkable what a little bit of ohms-law and arithmetic can do? Mathematics - don't make me laugh! smiley Mathematics is what English infants school teachers refer to when whining for a pay rise. To such a level are what the western-world's standards of education have been reduced. ---- Reg, G4FGQ |
#5
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"Reg Edwards" wrote in message ... "Dave VanHorn" wrote - Reg wrote - But to be on the safe side, allow for a dissipation of 1 watt per foot length of dipole wire which will then get warm in the centre, somewhat above ambient, when in a slight breeze. But the current distribution isn't linear, and the loss is I^2R, so I would think you'd have to know the max current, and work it that way. ============================ Yes Dave, I know. But I did say the wire gets warm at the centre. Sorry I forgot to say it remains cold at the ends except for the small conduction of heat along the wire. And it does not get quite so warm when it rains or snows. Actually, the current distribution along a 1/2-wave dipole is exactly a sinewaveform. This is arithmetically very convenient because the linearly distributed wire resistance then behaves as though it is lumped at the dipole centre with a value exactly half of the overall distributed value. Now the end-to-end resistance of a 1/2-wave, 160-meter dipole, made with 26-gauge copper-plated wire, is about 22 ohms. Therefore the feedpoint resistance of the antenna is the radiation resistance of 73 plus 22/2 ohms = 84 ohms. Therefore, with Tx power equal to 1000 watts and a current at the centre equal to 3.45 amps, the overall loss of power dissipated in the antenna wire is equal to 3.45 squared times half of the end-to-end conductor resistance of 11 ohms. Which (as I said in my previous message) equals 131 watts. Which raises the wire temperature a harmless handfull of a few degrees Celsius. Actual temperature, of course, depends on the open-air ambient temperature at noon, in June, in the New Mexico desert. Antenna radiating efficiency = 73/(73+11) = 84 percent, or a loss of 0.76 decibels, or 1/8th of an S-unit. Which, by no stretch of the imagination, is likely to influence the results of a contest. Isn't it remarkable what a little bit of ohms-law and arithmetic can do? Mathematics - don't make me laugh! smiley Mathematics is what English infants school teachers refer to when whining for a pay rise. To such a level are what the western-world's standards of education have been reduced. ---- Reg, G4FGQ Reg I went to public schools in Texas in the 50's and 60's. There were no standards then. School was a pathetic joke. If I hadn't had ham radio, cars and flying as teenage passions, I never would have learned math or physics. 73 H., NQ5H |
#6
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On Tue, 21 Sep 2004 09:04:00 -0500, "Dave VanHorn"
wrote: But to be on the safe side, allow for a dissipation of 1 watt per foot length of dipole wire which will then get warm in the centre, somewhat above ambient, when in a slight breeze. But the current distribution isn't linear, and the loss is I^2R, so I would think you'd have to know the max current, and work it that way. I don't think you should count on a perfect SWR match, either, and should size for some amount of mismatch. Worst case kind of thinking. Happy trails, Gary (net.yogi.bear) ------------------------------------------------ at the 51st percentile of ursine intelligence Gary D. Schwartz, Needham, MA, USA Please reply to: garyDOTschwartzATpoboxDOTcom |
#7
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Reg Edwards wrote:
"Dave VanHorn" wrote - But the current distribution isn't linear, and the loss is I^2R, so I would think you'd have to know the max current, and work it that way. ============================ Yes Dave, I know. But I did say the wire gets warm at the centre. Sorry I forgot to say it remains cold at the ends except for the small conduction of heat along the wire. And it does not get quite so warm when it rains or snows. This can be empirical verified by running a 1KW signal into the antenna and feeling the ends! (Kids! Don't try this at home!) Irv VE6BP -------------------- Irv Finkleman, Grampa/Ex-Navy/Old Fart/Ham Radio VE6BP Calgary, Alberta, Canada |
#8
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There is NO sharp dividing line between rec.radio.amateur.antenna and
politics. Or any other newsgroup. It's just a matter of keeping topics in sensible proportion. How else would I learn about Bush, puppy-dog Blair, atmospheric polution, the frequency of forest fires caused by 100-watt transmitters with short-whip mobile antennas high up in trees, and the impending state of the present excellent Californian winery's? ---- Reg, G4FGQ |
#9
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zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzt!
"Irv Finkleman" wrote in message ... Reg Edwards wrote: "Dave VanHorn" wrote - But the current distribution isn't linear, and the loss is I^2R, so I would think you'd have to know the max current, and work it that way. ============================ Yes Dave, I know. But I did say the wire gets warm at the centre. Sorry I forgot to say it remains cold at the ends except for the small conduction of heat along the wire. And it does not get quite so warm when it rains or snows. This can be empirical verified by running a 1KW signal into the antenna and feeling the ends! (Kids! Don't try this at home!) Irv VE6BP -------------------- Irv Finkleman, Grampa/Ex-Navy/Old Fart/Ham Radio VE6BP Calgary, Alberta, Canada |
#10
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What effect do you expect a mismatch to have on the current or the
current distribution on the antenna? Roy Lewallen, W7EL Gary S. wrote: On Tue, 21 Sep 2004 09:04:00 -0500, "Dave VanHorn" wrote: But to be on the safe side, allow for a dissipation of 1 watt per foot length of dipole wire which will then get warm in the centre, somewhat above ambient, when in a slight breeze. But the current distribution isn't linear, and the loss is I^2R, so I would think you'd have to know the max current, and work it that way. I don't think you should count on a perfect SWR match, either, and should size for some amount of mismatch. Worst case kind of thinking. Happy trails, Gary (net.yogi.bear) ------------------------------------------------ at the 51st percentile of ursine intelligence Gary D. Schwartz, Needham, MA, USA Please reply to: garyDOTschwartzATpoboxDOTcom |
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