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#31
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Damn Roger... It must be really tough being so superior. I was wondering if the glass is half full, or is it half empty? Ed |
#32
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Roger, you're right. I am stupid. Thank you for so kindly for pointing that out. We all need more "Elmers" like you. No, you're probably not stupid... maybe ignorant. You can fix that. If you don't own a copy of the ARRL Handbook, then GET ONE! Its the best single source of info you can get, and you will find answer to most if not all of your questions in there. Ed WB6SAT |
#33
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Roger, you're right. I am stupid. Thank you for so kindly for pointing that out. We all need more "Elmers" like you. No, you're probably not stupid... maybe ignorant. You can fix that. If you don't own a copy of the ARRL Handbook, then GET ONE! Its the best single source of info you can get, and you will find answer to most if not all of your questions in there. Ed WB6SAT |
#34
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To weed thru all this and answer the question I repeat -- see URL:
http://www.qsl.net/w4sat/five8th.htm Matching network at URL: http://www.arsqrp.com/ars/pages/back..._text/5_8.html And as pointed out several books were mentioned. ARRL Antenna handbook and ARRL Pubs Bill Orr's Books And good old http://www.google.com/ will get lots of places to look. -- Incognito By Necessity (:-( If you can't convince them, confuse them. - - -Harry S Truman |
#35
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To weed thru all this and answer the question I repeat -- see URL:
http://www.qsl.net/w4sat/five8th.htm Matching network at URL: http://www.arsqrp.com/ars/pages/back..._text/5_8.html And as pointed out several books were mentioned. ARRL Antenna handbook and ARRL Pubs Bill Orr's Books And good old http://www.google.com/ will get lots of places to look. -- Incognito By Necessity (:-( If you can't convince them, confuse them. - - -Harry S Truman |
#36
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Please help me out with the math. What is the length of a 5/8s wavelength 2 meter antenna? I've got something that might be able to be cut to the freq. You might try 5/8 of 2meters = 1.25Meters. Add a bit for trimming and there you are. Dave |
#37
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Please help me out with the math. What is the length of a 5/8s wavelength 2 meter antenna? I've got something that might be able to be cut to the freq. You might try 5/8 of 2meters = 1.25Meters. Add a bit for trimming and there you are. Dave |
#38
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Please help me out with the math. What is the length of a 5/8s wavelength 2
meter antenna? I've got something that might be able to be cut to the freq. Moody- Did you realize what a stimulating topic this was going to be? Perhaps I can help by announcing that there are two slightly different legitimate answers. First, radio waves travel very close to 300 million meters per second. The two meter band is roughly at a frequency of 150 million Hertz, so one wavelength would be 300 million divided by 150 million. I think you get the idea, and can use your exact frequency to get the exact wavelength. In the case of a 5/8th wavelength antenna, simply multiply the calculated wavelength by 5/8 (or 0.625). (One inch equals 0.0254 meters.) To use such an antenna, you must find a way to connect your transmission line to the antenna and a ground plane, so that it matches. In other words, you want to transfer the maximum amount of power to the antenna so it can be radiated, and reflect the minimum amount of power back to the transmitter. The beauty of a 5/8th wavelength (ground plane) antenna, is that it is extremely easy to match. Its input impedance is 50 Ohms resistive in series with a small amount of capacitance. Therefore you need a small amount of series inductance to match it. Some higher-frequency examples use the stainless element itself, wound in a small coil near its base. The other "legitimate" answer is that a given 5/8th wavelength antenna you buy, may actually be 0.58 wavelength, NOT 0.625. Such antennas are usually called 5/8th because of the confusion between 0.58 and 5/8. The beauty of a 0.58 wavelength (groundplane) antenna, is that it concentrates the maximum amount of power towards the horizon, compared to other similarly constructed antennas (according to my Antennas Professor, 35 years ago). While it is true that there is a small lobe towards the sky above, the main lobe is sharper than the lobe of a quarter wave ground plane, and is aimed almost directly at the horizon. If the vertical element were any longer (say, 0.625 wavelength), the lobe pointed up would increase and sap some of the power from the lobe towards the horizon. If it were shorter, the main lobe would be fatter and power would be spread over a larger, slightly higher angle. A drawback of the 0.58 wavelength antenna is that it is not as easily matched. Such antennas are often matched with a tapped coil. The bottom of the coil is connected to ground, the top to the antenna element, and the co-axial transmission line center conductor is connected to a tap on the coil. 73, Fred, K4DII |
#39
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Please help me out with the math. What is the length of a 5/8s wavelength 2
meter antenna? I've got something that might be able to be cut to the freq. Moody- Did you realize what a stimulating topic this was going to be? Perhaps I can help by announcing that there are two slightly different legitimate answers. First, radio waves travel very close to 300 million meters per second. The two meter band is roughly at a frequency of 150 million Hertz, so one wavelength would be 300 million divided by 150 million. I think you get the idea, and can use your exact frequency to get the exact wavelength. In the case of a 5/8th wavelength antenna, simply multiply the calculated wavelength by 5/8 (or 0.625). (One inch equals 0.0254 meters.) To use such an antenna, you must find a way to connect your transmission line to the antenna and a ground plane, so that it matches. In other words, you want to transfer the maximum amount of power to the antenna so it can be radiated, and reflect the minimum amount of power back to the transmitter. The beauty of a 5/8th wavelength (ground plane) antenna, is that it is extremely easy to match. Its input impedance is 50 Ohms resistive in series with a small amount of capacitance. Therefore you need a small amount of series inductance to match it. Some higher-frequency examples use the stainless element itself, wound in a small coil near its base. The other "legitimate" answer is that a given 5/8th wavelength antenna you buy, may actually be 0.58 wavelength, NOT 0.625. Such antennas are usually called 5/8th because of the confusion between 0.58 and 5/8. The beauty of a 0.58 wavelength (groundplane) antenna, is that it concentrates the maximum amount of power towards the horizon, compared to other similarly constructed antennas (according to my Antennas Professor, 35 years ago). While it is true that there is a small lobe towards the sky above, the main lobe is sharper than the lobe of a quarter wave ground plane, and is aimed almost directly at the horizon. If the vertical element were any longer (say, 0.625 wavelength), the lobe pointed up would increase and sap some of the power from the lobe towards the horizon. If it were shorter, the main lobe would be fatter and power would be spread over a larger, slightly higher angle. A drawback of the 0.58 wavelength antenna is that it is not as easily matched. Such antennas are often matched with a tapped coil. The bottom of the coil is connected to ground, the top to the antenna element, and the co-axial transmission line center conductor is connected to a tap on the coil. 73, Fred, K4DII |
#40
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Instead of posting look the formula up in your study guide. Learn how to
find your information in the guides and Tec manuals first. Go out and pick up a copy of the ARRL Handbook and learn how to use it. It has the basic formulas in it and how to put them to practical use. I had to question how you got your license also not knowing that formula. I will give you 1 piece of advice. When you are working with metric DON'T Convert just keep it all metric. "Moody1951" wrote in message ... Roger, you're right. I am stupid. Thank you for so kindly for pointing that out. We all need more "Elmers" like you. |
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