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#241
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#242
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"Kim W5TIT" wrote in message ...
"Mike Coslo" wrote in message ... From http://www.oakvilleamateurs.net/news...s/hb200302.pdf . . ."For most 40-meters, the most practical antenna is the 1/4-wave dipole (66 feet in total length) up at least 33 feet in the air. If you've never worked (or heard) Europe on 40, it's likely your dipole is too low. The challenge grows on 80 where your quarter wave dipole (133' 9") needs to be . . . Bilge. All of it. A 66 foot dipole is roughly a *half wave* dipole on 40M and a 134 foot dipole is roughly a *half wave* dipole on 80M. A 33 foot long center-fed dipole is a quarter wavelength long on 40M but it is not resonant on 40M and ya better not get stupid and feed it with coax then just plug it into the back of yer radio if ya wanna work anybody with it. Ask any Novice . . . w3rv |
#243
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#244
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#246
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The way I was taught to think of it was that the length (overall) is the
reference to the "length" of the dipole antenna. For example, a "half-wave" dipole antenna would be a "quarter-wave" in length on each side of the center insulator or center point. So a full wavelength dipole antenna would have each "side" of the dipole being one-half wavelength each. Oh well....... -- Ryan, KC8PMX FF1-FF2-MFR-(pending NREMT-B!) --. --- -.. ... .- -. --. . .-.. ... .- .-. . ..-. .. .-. . ..-. ... --. .... - . .-. ... "Dan/W4NTI" w4nti@get rid of this mindspring.com wrote in message link.net... The question refered to a DIPOLE. A dipole is at least 1/2 wavelength long. See comments by Jeffery Herman for further clarification on a 'dipole'. Dan/W4NTI "Ryan, KC8PMX" wrote in message ... Pure bull**** Dan, the formula changes for a quarter wave versus a half wave versus a full wave. 468/freq. in Mhz is for a half-wave dipole. The specific for a quarter-wave is half that. And so on and so forth. If the person specified which length they were looking for I would have popped up the correct answer, as far out to the right of the decimal as you want (yes, calculated by hand, not calculator. I do it the old fashioned way), but they didn't specify which wavelength they were looking for. What is the length of a dipole for 14.240Mhz? Of what wavelength???? That is an important factor in the equation. Congratulations you have just proven you have NO CONCEPT of what was asked. Does 468 divided by Frequency in Mhz mean anything to you? Yep... for a half-wave dipole. Dan/W4NTI |
#247
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"Brian Kelly" wrote in message
om... "Kim W5TIT" wrote in message ... "Mike Coslo" wrote in message ... From http://www.oakvilleamateurs.net/news...s/hb200302.pdf . . ."For most 40-meters, the most practical antenna is the 1/4-wave dipole (66 feet in total length) up at least 33 feet in the air. If you've never worked (or heard) Europe on 40, it's likely your dipole is too low. The challenge grows on 80 where your quarter wave dipole (133' 9") needs to be . . . Bilge. All of it. A 66 foot dipole is roughly a *half wave* dipole on 40M and a 134 foot dipole is roughly a *half wave* dipole on 80M. A 33 foot long center-fed dipole is a quarter wavelength long on 40M but it is not resonant on 40M and ya better not get stupid and feed it with coax then just plug it into the back of yer radio if ya wanna work anybody with it. Ask any Novice . . . w3rv Newp, sorry. A 40M 1/4-wave dipole can be made to resonate just fine and work wonderfully. Its position to the ground and center angle have everything to do with how well it will radiate. And, using a balun or not doesn't change the whole concept of using a 1/4-wave dipole at any frequency. Whether you want them to or not, they work. Kim W5TIT |
#248
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Newp, sorry. A 40M 1/4-wave dipole can be made to resonate just fine and
work wonderfully. Its position to the ground and center angle have everything to do with how well it will radiate. And, using a balun or not doesn't change the whole concept of using a 1/4-wave dipole at any frequency. Whether you want them to or not, they work. Kim W5TIT Proof Positive the written is FAILURE. |
#249
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Kim W5TIT wrote:
Kim W5TIT -- done with the topic, but changed to an appropriately titled topic. After all, we wouldn't want a search on "1/4 wave dipole" to miss all this pertinent, scientific discussion. *yeah, right* Does a 1/4 wave ground plane antenna count? ;-) |
#250
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Kim W5TIT wrote:
Newp, sorry. A 40M 1/4-wave dipole can be made to resonate just fine and work wonderfully. Its position to the ground and center angle have everything to do with how well it will radiate. And, using a balun or not doesn't change the whole concept of using a 1/4-wave dipole at any frequency. Whether you want them to or not, they work. A couple points here Kim. According to the ARRL handbook 2003 edition, chapte 20 page 4: A fundamental form of antenna is a wire whose length is half the transmitting wavelength. It is the unit from which many more complex forms of antennas are constructed and is known as a dipole antenna. It goes on from there if you want more. Next I modeled two antennas in EZNEC. One is a half wave dipole for the middle of the 40 meter band at 7.150 mHz. Each leg of the antenna is approximately 1/4 wavelength long at 65.45 feet. This antenna models out at an SWR of a little over 1.5:1 at the center frequency, and 2:1 at 7.3 mHz and a touch over 2 mHz at 7 mHz with the antenna at 50 feet, the take off angle is 35 degrees. All in all, not too bad an antenna. Most modern rigs will handle the antenna without a tuner, or simply with their internal tuner. Next, I modeled a quarter wave dipole for the same frequency and all other paramaters. With the legs at 32.7 feet, the antenna now displays somewhat near infinite SWR. The take off angle has now risen to 54 degrees. That antenna is simply not going to work well at all. - Mike KB3EIA - |
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