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What is the length of a 5/8s wavelength 2 meter antenna?
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. Thanks |
"Moody1951" wrote in message ... 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. Thanks Lets assume you want a center frequency of 146 megahertz... 300/146=2.057945m (round it to nearest mm 2.058m) 2.058/8=0.25725m 0.25725x5=1.28625m (round it to nearest mm 1.286m) Now I have a few questions... How the ^%$#(*&$ do you get to even own a 2m radio without knowing how to do this ELEMENTARY calculation? Do you have a licence? Have you learnt absolutely nothing? This formula is the first one in the book together with Ohm's Law! 73 Roger ZR3RC |
"Moody1951" wrote in message ... 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. Thanks Lets assume you want a center frequency of 146 megahertz... 300/146=2.057945m (round it to nearest mm 2.058m) 2.058/8=0.25725m 0.25725x5=1.28625m (round it to nearest mm 1.286m) Now I have a few questions... How the ^%$#(*&$ do you get to even own a 2m radio without knowing how to do this ELEMENTARY calculation? Do you have a licence? Have you learnt absolutely nothing? This formula is the first one in the book together with Ohm's Law! 73 Roger ZR3RC |
Neat calculator at URL:
http://www.geocities.com/kk5hy/calc.html You can cut it for hi, lo, or mid band -- Incognito By Necessity (:-( If you can't convince them, confuse them. - - -Harry S Truman "Moody1951" wrote in message ... 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. Thanks |
Neat calculator at URL:
http://www.geocities.com/kk5hy/calc.html You can cut it for hi, lo, or mid band -- Incognito By Necessity (:-( If you can't convince them, confuse them. - - -Harry S Truman "Moody1951" wrote in message ... 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. Thanks |
Damn Roger... It must be really tough being so superior.
"Roger Conroy" wrote in message ... "Moody1951" wrote in message ... 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. Thanks Lets assume you want a center frequency of 146 megahertz... 300/146=2.057945m (round it to nearest mm 2.058m) 2.058/8=0.25725m 0.25725x5=1.28625m (round it to nearest mm 1.286m) Now I have a few questions... How the ^%$#(*&$ do you get to even own a 2m radio without knowing how to do this ELEMENTARY calculation? Do you have a licence? Have you learnt absolutely nothing? This formula is the first one in the book together with Ohm's Law! 73 Roger ZR3RC |
Damn Roger... It must be really tough being so superior.
"Roger Conroy" wrote in message ... "Moody1951" wrote in message ... 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. Thanks Lets assume you want a center frequency of 146 megahertz... 300/146=2.057945m (round it to nearest mm 2.058m) 2.058/8=0.25725m 0.25725x5=1.28625m (round it to nearest mm 1.286m) Now I have a few questions... How the ^%$#(*&$ do you get to even own a 2m radio without knowing how to do this ELEMENTARY calculation? Do you have a licence? Have you learnt absolutely nothing? This formula is the first one in the book together with Ohm's Law! 73 Roger ZR3RC |
While I do not claim superiority in my knowledge, I must wonder myself
sometimes about those with a license. I know one person who doesn't know what a "ground" symbol looks like in a schematic - and "that" is one of the "basic"questions on the exams. I know another who has no clue what a "fuse" does. Now, "that" is sad. Calculations? Even when learned, some do have math problems - to some extent, I can understand that. Learning formulas and being able to do them, is not always the same.. Sounds contradictory I know, but I've seen that myself a few times. It amazes me sometimes..... Hell, I know people who don't know the resistor color code, can't figure out resistors in series or parallel, etc. "All" or any of the things they learned to get their license. Most people just do what it takes to get a license. Once they start yakking, they lose the knowledge from lack of use of it. Even that is hard to fathom considering the many technical chats one would tend to hear. YEP! It sure is hard to imagine, but it is true........ sad but true! Lou "J Shrum" wrote in message ... Damn Roger... It must be really tough being so superior. "Roger Conroy" wrote in message ... "Moody1951" wrote in message ... 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. Thanks Lets assume you want a center frequency of 146 megahertz... 300/146=2.057945m (round it to nearest mm 2.058m) 2.058/8=0.25725m 0.25725x5=1.28625m (round it to nearest mm 1.286m) Now I have a few questions... How the ^%$#(*&$ do you get to even own a 2m radio without knowing how to do this ELEMENTARY calculation? Do you have a licence? Have you learnt absolutely nothing? This formula is the first one in the book together with Ohm's Law! 73 Roger ZR3RC |
While I do not claim superiority in my knowledge, I must wonder myself
sometimes about those with a license. I know one person who doesn't know what a "ground" symbol looks like in a schematic - and "that" is one of the "basic"questions on the exams. I know another who has no clue what a "fuse" does. Now, "that" is sad. Calculations? Even when learned, some do have math problems - to some extent, I can understand that. Learning formulas and being able to do them, is not always the same.. Sounds contradictory I know, but I've seen that myself a few times. It amazes me sometimes..... Hell, I know people who don't know the resistor color code, can't figure out resistors in series or parallel, etc. "All" or any of the things they learned to get their license. Most people just do what it takes to get a license. Once they start yakking, they lose the knowledge from lack of use of it. Even that is hard to fathom considering the many technical chats one would tend to hear. YEP! It sure is hard to imagine, but it is true........ sad but true! Lou "J Shrum" wrote in message ... Damn Roger... It must be really tough being so superior. "Roger Conroy" wrote in message ... "Moody1951" wrote in message ... 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. Thanks Lets assume you want a center frequency of 146 megahertz... 300/146=2.057945m (round it to nearest mm 2.058m) 2.058/8=0.25725m 0.25725x5=1.28625m (round it to nearest mm 1.286m) Now I have a few questions... How the ^%$#(*&$ do you get to even own a 2m radio without knowing how to do this ELEMENTARY calculation? Do you have a licence? Have you learnt absolutely nothing? This formula is the first one in the book together with Ohm's Law! 73 Roger ZR3RC |
Roger, you're right. I am stupid. Thank you for so kindly for pointing that
out. We all need more "Elmers" like you. |
Roger, you're right. I am stupid. Thank you for so kindly for pointing that
out. We all need more "Elmers" like you. |
Lou,
I do agree... I understand that many folks study just the bare minimum to get that "2meter CB ticket" and thats it. But I don't agree w/ the public tongue lashing... Ok, I'm done... "Lou" wrote in message ... While I do not claim superiority in my knowledge, I must wonder myself sometimes about those with a license. I know one person who doesn't know what a "ground" symbol looks like in a schematic - and "that" is one of the "basic"questions on the exams. I know another who has no clue what a "fuse" does. Now, "that" is sad. Calculations? Even when learned, some do have math problems - to some extent, I can understand that. Learning formulas and being able to do them, is not always the same.. Sounds contradictory I know, but I've seen that myself a few times. It amazes me sometimes..... Hell, I know people who don't know the resistor color code, can't figure out resistors in series or parallel, etc. "All" or any of the things they learned to get their license. Most people just do what it takes to get a license. Once they start yakking, they lose the knowledge from lack of use of it. Even that is hard to fathom considering the many technical chats one would tend to hear. YEP! It sure is hard to imagine, but it is true........ sad but true! Lou "J Shrum" wrote in message ... Damn Roger... It must be really tough being so superior. "Roger Conroy" wrote in message ... "Moody1951" wrote in message ... 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. Thanks Lets assume you want a center frequency of 146 megahertz... 300/146=2.057945m (round it to nearest mm 2.058m) 2.058/8=0.25725m 0.25725x5=1.28625m (round it to nearest mm 1.286m) Now I have a few questions... How the ^%$#(*&$ do you get to even own a 2m radio without knowing how to do this ELEMENTARY calculation? Do you have a licence? Have you learnt absolutely nothing? This formula is the first one in the book together with Ohm's Law! 73 Roger ZR3RC |
Lou,
I do agree... I understand that many folks study just the bare minimum to get that "2meter CB ticket" and thats it. But I don't agree w/ the public tongue lashing... Ok, I'm done... "Lou" wrote in message ... While I do not claim superiority in my knowledge, I must wonder myself sometimes about those with a license. I know one person who doesn't know what a "ground" symbol looks like in a schematic - and "that" is one of the "basic"questions on the exams. I know another who has no clue what a "fuse" does. Now, "that" is sad. Calculations? Even when learned, some do have math problems - to some extent, I can understand that. Learning formulas and being able to do them, is not always the same.. Sounds contradictory I know, but I've seen that myself a few times. It amazes me sometimes..... Hell, I know people who don't know the resistor color code, can't figure out resistors in series or parallel, etc. "All" or any of the things they learned to get their license. Most people just do what it takes to get a license. Once they start yakking, they lose the knowledge from lack of use of it. Even that is hard to fathom considering the many technical chats one would tend to hear. YEP! It sure is hard to imagine, but it is true........ sad but true! Lou "J Shrum" wrote in message ... Damn Roger... It must be really tough being so superior. "Roger Conroy" wrote in message ... "Moody1951" wrote in message ... 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. Thanks Lets assume you want a center frequency of 146 megahertz... 300/146=2.057945m (round it to nearest mm 2.058m) 2.058/8=0.25725m 0.25725x5=1.28625m (round it to nearest mm 1.286m) Now I have a few questions... How the ^%$#(*&$ do you get to even own a 2m radio without knowing how to do this ELEMENTARY calculation? Do you have a licence? Have you learnt absolutely nothing? This formula is the first one in the book together with Ohm's Law! 73 Roger ZR3RC |
Geez...maybe he'll convert this over to U.S. measurement!
"Roger Conroy" wrote in message ... "Moody1951" wrote in message ... 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. Thanks Lets assume you want a center frequency of 146 megahertz... 300/146=2.057945m (round it to nearest mm 2.058m) 2.058/8=0.25725m 0.25725x5=1.28625m (round it to nearest mm 1.286m) Now I have a few questions... How the ^%$#(*&$ do you get to even own a 2m radio without knowing how to do this ELEMENTARY calculation? Do you have a licence? Have you learnt absolutely nothing? This formula is the first one in the book together with Ohm's Law! 73 Roger ZR3RC |
Geez...maybe he'll convert this over to U.S. measurement!
"Roger Conroy" wrote in message ... "Moody1951" wrote in message ... 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. Thanks Lets assume you want a center frequency of 146 megahertz... 300/146=2.057945m (round it to nearest mm 2.058m) 2.058/8=0.25725m 0.25725x5=1.28625m (round it to nearest mm 1.286m) Now I have a few questions... How the ^%$#(*&$ do you get to even own a 2m radio without knowing how to do this ELEMENTARY calculation? Do you have a licence? Have you learnt absolutely nothing? This formula is the first one in the book together with Ohm's Law! 73 Roger ZR3RC |
Ok lets start this over again
Hi Moody, The ansewr to your question, if you intend to use it on the upper portion of the band (tuned to 146Mhz) would be 48.12 inches. Aside from your asking antenna question here, also check out the ARRL Handbook, as you will find the answers to simple questions, others get annoyed at LOL also visit the http://www.qsl.net/w4sat/antenna.htm website. As far as the point you expressed Bob, I agree with you somewhat. Not all Techs dont know anything. I have spoken to many Advanced/Extra that cant figure out the length of a dipole for 40m, or how to program the memory in the 2m radio. Even go as far as "you are not on frequency, and you dont need to say over on a repeater". Now it makes me made when, me being a Tech needs to answer these questions Take in to the account of why many join the ham ranks. Not all are technical minded people, or not yet atleast 73 Steve KC2GOG "Moody1951" wrote in message ... 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. Thanks |
Ok lets start this over again
Hi Moody, The ansewr to your question, if you intend to use it on the upper portion of the band (tuned to 146Mhz) would be 48.12 inches. Aside from your asking antenna question here, also check out the ARRL Handbook, as you will find the answers to simple questions, others get annoyed at LOL also visit the http://www.qsl.net/w4sat/antenna.htm website. As far as the point you expressed Bob, I agree with you somewhat. Not all Techs dont know anything. I have spoken to many Advanced/Extra that cant figure out the length of a dipole for 40m, or how to program the memory in the 2m radio. Even go as far as "you are not on frequency, and you dont need to say over on a repeater". Now it makes me made when, me being a Tech needs to answer these questions Take in to the account of why many join the ham ranks. Not all are technical minded people, or not yet atleast 73 Steve KC2GOG "Moody1951" wrote in message ... 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. Thanks |
On Tue, 6 Apr 2004 09:27:58 +0200, "Roger Conroy"
wrote: Now I have a few questions... How the ^%$#(*&$ do you get to even own a 2m radio without knowing how to do this ELEMENTARY calculation? Do you have a licence? Have you learnt absolutely nothing? This formula is the first one in the book together with Ohm's Law! Perhaps he took the test over a year ago, has only been using a HT, and is now wanting to get into mobile use? Let me ask you a few questions: How far in advance of a turn are you required to use your turn signal? What is the maximum distance you may enter a bike lane prior to making a turn? You may use your hi beams if a car coming towards you is more than ____ feet away, or if a car is in front of you in the same direction as you, more than _____ feet away. Gee, you don't know? How the &*^#*$@ did you get your drivers license? Get the point? Evan To reply, remove TheObvious from my e-mail address. |
On Tue, 6 Apr 2004 09:27:58 +0200, "Roger Conroy"
wrote: Now I have a few questions... How the ^%$#(*&$ do you get to even own a 2m radio without knowing how to do this ELEMENTARY calculation? Do you have a licence? Have you learnt absolutely nothing? This formula is the first one in the book together with Ohm's Law! Perhaps he took the test over a year ago, has only been using a HT, and is now wanting to get into mobile use? Let me ask you a few questions: How far in advance of a turn are you required to use your turn signal? What is the maximum distance you may enter a bike lane prior to making a turn? You may use your hi beams if a car coming towards you is more than ____ feet away, or if a car is in front of you in the same direction as you, more than _____ feet away. Gee, you don't know? How the &*^#*$@ did you get your drivers license? Get the point? Evan To reply, remove TheObvious from my e-mail address. |
Roger. Realize. It's just a hobby. Don't chase em' away.
|
Roger. Realize. It's just a hobby. Don't chase em' away.
|
"Moody1951" wrote in message
... Roger. Realize. It's just a hobby. Don't chase em' away. Heck no, don't chase them, EDUCATE them. Asking questions, isn't stupid.. it is the unasked question and the assumption thereof which is stupid. Lou |
"Moody1951" wrote in message
... Roger. Realize. It's just a hobby. Don't chase em' away. Heck no, don't chase them, EDUCATE them. Asking questions, isn't stupid.. it is the unasked question and the assumption thereof which is stupid. Lou |
"Moody1951" wrote in message ... 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. Others have given you the length. They failed to mention that the impedance is not 50 ohms and you must match that to the coax/rig. You will have to research that for yourself, but usually a coil is used in series with the antenna at the base of it. |
"Moody1951" wrote in message ... 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. Others have given you the length. They failed to mention that the impedance is not 50 ohms and you must match that to the coax/rig. You will have to research that for yourself, but usually a coil is used in series with the antenna at the base of it. |
"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. Whilst he could've been a little more 'tactful', you must admit that it was a question that any newcomer studying for their licence should've known, let alone someone actually in the hobby.... But, that's just my opinion... Martin, VK2UMJ |
"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. Whilst he could've been a little more 'tactful', you must admit that it was a question that any newcomer studying for their licence should've known, let alone someone actually in the hobby.... But, that's just my opinion... Martin, VK2UMJ |
On Tue, 6 Apr 2004 19:29:45 -0400, "Ralph Mowery"
wrote: "Moody1951" wrote in message ... 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. Others have given you the length. They failed to mention that the impedance is not 50 ohms and you must match that to the coax/rig. You will have to research that for yourself, but usually a coil is used in series with the antenna at the base of it. Also relevant: The calculated length is close, but factors like material type, thickness, etc, mean that the actual length could be a little different. Electrical length is what counts, not physical. Best bet is to take the calculated length as mentioned earlier, add a little bit, and cut to that greater length. Then test the antenna with an SWR meter, trim a little shorter, and test again to optimize SWR across the band of interest. You will never hit 1:1 (more of a theoretical goal) but below 1:1.5 across the 2M band is fine. Start your testing at a low power, until you know the SWR is below 1:2. Happy trails, Gary (net.yogi.bear) ------------------------------------------------ at the 51st percentile of ursine intelligence Gary D. Schwartz, Needham, MA, USA Please reply to: garyDOTschwartzATpoboxDOTcom |
On Tue, 6 Apr 2004 19:29:45 -0400, "Ralph Mowery"
wrote: "Moody1951" wrote in message ... 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. Others have given you the length. They failed to mention that the impedance is not 50 ohms and you must match that to the coax/rig. You will have to research that for yourself, but usually a coil is used in series with the antenna at the base of it. Also relevant: The calculated length is close, but factors like material type, thickness, etc, mean that the actual length could be a little different. Electrical length is what counts, not physical. Best bet is to take the calculated length as mentioned earlier, add a little bit, and cut to that greater length. Then test the antenna with an SWR meter, trim a little shorter, and test again to optimize SWR across the band of interest. You will never hit 1:1 (more of a theoretical goal) but below 1:1.5 across the 2M band is fine. Start your testing at a low power, until you know the SWR is below 1:2. Happy trails, Gary (net.yogi.bear) ------------------------------------------------ at the 51st percentile of ursine intelligence Gary D. Schwartz, Needham, MA, USA Please reply to: garyDOTschwartzATpoboxDOTcom |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
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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