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#1
January 22nd 08, 08:51 PM
posted to rec.radio.amateur.antenna
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wire size
I have a home brew dipole antenna made from #22 copper What is ther
maximum power that it can handle. Support is not a problem. I want to test it for max power using a 8877 which will blow if the wire opens, and they are costly. Ofcourse I would like a bit of safety in hand. Does minimum wire size vary much dependent on band useage? I have no idea what manufactures use for commercial style antennas! Art |
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#2
January 22nd 08, 08:59 PM
posted to rec.radio.amateur.antenna
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wire size
art wrote:
I have a home brew dipole antenna made from #22 copper What is ther maximum power that it can handle. If it is a 1/2WL dipole, the current will be maximum at the feedpoint. Will #22 wire handle your current at the feedpoint? Skin depth is frequency dependent. -- 73, Cecil http://www.w5dxp.com |
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#3
January 23rd 08, 07:49 PM
posted to rec.radio.amateur.antenna
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wire size
On Jan 22, 3:51*pm, art wrote:
I have a home brew dipole antenna made from #22 copper What is ther maximum power that it can handle. Support is not a problem. I want to test it for max power using a 8877 which will blow if the wire opens, and they are costly. Ofcourse I would like a bit of safety in hand. Does minimum wire size vary much dependent on band useage? I have no idea what manufactures use for commercial style antennas! Wow! An 8877 could develop 1.5 to 2kW output power (if done in a part of a world where it's legal for a ham to use that much power.) 2kW into a 50 ohm load is a current of 6 or 7 amps, assuming it's a perfect match/no standing waves. The fusing current of 22AWG copper wire is about 40 Amps. So if everything is working and matched, it won't melt. The higher you go in frequency, the more you'll have to derate the above, but for low HF it'll be not too bad. But geeze.... you've got a multi-kilowatt amp and can't afford anything better than 22AWG wire??? Traditional rule-of-thumb for ham wire antennas would say that if you're pumping more than a kilowatt in, you want at least 12 gauge or 14 gauge wire. There's also the N.E.C. specs, which say that copper antenna wires have to be thicker than 14 gauge up to 150' spans, and thicker than 10 gauge over 150' spans. Tim N3QE |
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#4
January 24th 08, 12:31 AM
posted to rec.radio.amateur.antenna
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wire size
Tim Shoppa wrote:
On Jan 22, 3:51 pm, art wrote: I have a home brew dipole antenna made from #22 copper What is ther maximum power that it can handle. Support is not a problem. I want to test it for max power using a 8877 which will blow if the wire opens, and they are costly. Ofcourse I would like a bit of safety in hand. Does minimum wire size vary much dependent on band useage? I have no idea what manufactures use for commercial style antennas! Wow! An 8877 could develop 1.5 to 2kW output power (if done in a part of a world where it's legal for a ham to use that much power.) 2kW into a 50 ohm load is a current of 6 or 7 amps, assuming it's a perfect match/no standing waves. The fusing current of 22AWG copper wire is about 40 Amps. So if everything is working and matched, it won't melt. That's the DC fusing current.... As an earlier poster mentioned, skin effect means that the current is being carried in a thin layer on the surface, so the heating might be more. Of course, the hot layer is also closer to the air. The higher you go in frequency, the more you'll have to derate the above, but for low HF it'll be not too bad. But geeze.... you've got a multi-kilowatt amp and can't afford anything better than 22AWG wire??? Traditional rule-of-thumb for ham wire antennas would say that if you're pumping more than a kilowatt in, you want at least 12 gauge or 14 gauge wire. There's also the N.E.C. specs, which say that copper antenna wires have to be thicker than 14 gauge up to 150' spans, and thicker than 10 gauge over 150' spans. The NEC rules are for mechanical strength, not current carrying capacity. One might also wonder about corona discharge at the ends of the dipole... Tim N3QE |
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#5
January 24th 08, 03:40 AM
posted to rec.radio.amateur.antenna
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wire size
On 23 Jan, 16:31, Jim Lux wrote:
Tim Shoppa wrote: On Jan 22, 3:51 pm, art wrote: I have a home brew dipole antenna made from #22 copper What is ther maximum power that it can handle. Support is not a problem. I want to test it for max power using a 8877 which will blow if the wire opens, and they are costly. Ofcourse I would like a bit of safety in hand. Does minimum wire size vary much dependent on band useage? I have no idea what manufactures use for commercial style antennas! Wow! An 8877 could develop 1.5 to 2kW output power (if done in a part of a world where it's legal for a ham to use that much power.) 2kW into a 50 ohm load is a current of 6 or 7 amps, assuming it's a perfect match/no standing waves. The fusing current of 22AWG copper wire is about 40 Amps. So if everything is working and matched, it won't melt. That's the DC fusing current.... As an earlier poster mentioned, skin effect means that the current is being carried in a thin layer on the surface, so the heating might be more. *Of course, the hot layer is also closer to the air. The higher you go in frequency, the more you'll have to derate the above, but for low HF it'll be not too bad. But geeze.... you've got a multi-kilowatt amp and can't afford anything better than 22AWG wire??? Traditional rule-of-thumb for ham wire antennas would say that if you're pumping more than a kilowatt in, you want at least 12 gauge or 14 gauge wire. There's also the N.E.C. specs, which say that copper antenna wires have to be thicker than 14 gauge up to 150' spans, and thicker than 10 gauge over 150' spans. The NEC rules are for mechanical strength, not current carrying capacity. One might also wonder about corona discharge at the ends of the dipole... Tim N3QE- Hide quoted text - - Show quoted text -- Hide quoted text - - Show quoted text - Actually it is a full wave length helix winding for 160M. The teflon coated wire was what I had on hand.I will only be using 100 watts or so but you never know when the urge comes up. I have a motor driven reflector on it so I will be checking out the directivity at different close spacings.When I finally settle on a design the wire will be thicker magnet wire. Thanks for all the info. As for heat it is mighty cold here so short transmissions should work out o.k. Regards Art |
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#6
January 25th 08, 12:57 AM
posted to rec.radio.amateur.antenna
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wire size
On 23 Jan, 19:40, art wrote:
On 23 Jan, 16:31, Jim Lux wrote: Tim Shoppa wrote: On Jan 22, 3:51 pm, art wrote: I have a home brew dipole antenna made from #22 copper What is ther maximum power that it can handle. Support is not a problem. I want to test it for max power using a 8877 which will blow if the wire opens, and they are costly. Ofcourse I would like a bit of safety in hand. Does minimum wire size vary much dependent on band useage? I have no idea what manufactures use for commercial style antennas! Wow! An 8877 could develop 1.5 to 2kW output power (if done in a part of a world where it's legal for a ham to use that much power.) 2kW into a 50 ohm load is a current of 6 or 7 amps, assuming it's a perfect match/no standing waves. The fusing current of 22AWG copper wire is about 40 Amps. So if everything is working and matched, it won't melt. That's the DC fusing current.... As an earlier poster mentioned, skin effect means that the current is being carried in a thin layer on the surface, so the heating might be more. *Of course, the hot layer is also closer to the air. The higher you go in frequency, the more you'll have to derate the above, but for low HF it'll be not too bad. But geeze.... you've got a multi-kilowatt amp and can't afford anything better than 22AWG wire??? Traditional rule-of-thumb for ham wire antennas would say that if you're pumping more than a kilowatt in, you want at least 12 gauge or 14 gauge wire. There's also the N.E.C. specs, which say that copper antenna wires have to be thicker than 14 gauge up to 150' spans, and thicker than 10 gauge over 150' spans. The NEC rules are for mechanical strength, not current carrying capacity.. One might also wonder about corona discharge at the ends of the dipole.... Tim N3QE- Hide quoted text - - Show quoted text -- Hide quoted text - - Show quoted text - Actually it is a full wave length helix winding for 160M. The teflon coated wire was what I had on hand.I will only be using 100 watts or so but you never know when the urge comes up. I have a motor driven reflector on it so I will be checking out the directivity at different close spacings.When I finally settle on a design the wire will be thicker magnet wire. Thanks for all the info. As for heat it is mighty cold here so short transmissions should work out o.k. Regards Art- Hide quoted text - - Show quoted text - It has been very cold these last few days working on antennas. Just finished putting up anew 160M antenna but have not checked it yet as I am so tired.It is like a TV antenna at 70 feet. Have a reflector on it made of aluminum mesh plus a motor to place the reflector within six inches of the driven element to about 30 inches from the driven element.Now have to wire up the rotor and the reflector motor and then chart the LC for all bands.HopefullyI will be close first time for the top band.Next antenna to brew will be around 1 cuft for 160M probably out of #20 wire this time but I do need a rest from antennas! Regards Art Unwin KB9MZ.....XG(uk) |
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