|
Loading Coil Q
I have aluminum poles of three diameters, 1.5, 1, and .5 inches. I have enough of the first two to create a pole of about 15 feet each and about 8 to 9 feet with the 1/5 inch poles. The poles are no more than 4 feet long each, but they are able to tuck inside each other, at least for the same diameter. What I want to do is to make up a 'kit' with these that I can take to the field to setup whatever antenna I want to use at the time. For example, I might set it up as a 20 meter vertical in one configuration, but in the evening, I might reconfigure it to 75 meters or 15, or 30 or whatever I desire. One consideration is to create a high-q coil for it. I am thinking of using 1/4 inch copper tubing to make a ten to twelve inch diameter coil so I can match it to the lower bands. I have been reading that base loaded coils have to be matched to the antenna, but center loaded verticals are more closely matched to 50 ohms. from what I have been reading, the center loaded coil requires more turns and a top loaded coil even more. A capacity hat is also a viable option. I am wondering how much I am helping or hurting myself with the larger coil or if I would be better off with a smaller coil. One thought is to connect x number of poles, then the coil, then another set of poles or a whip to make the final adjustment for the match or to match the antenna by tapping the coil. I am open to all suggestions, but I am interested in knowing the best location for the coil and the best size for it. Thank you -- 73 for now Buck N4PGW |
Program LOADCOIL models short, coil-loaded, vertical antennas.
Amongst other things it allows the coil to slide up and down the antenna (from the keyboard) and find the coil location at which power radiating efficiency is maximised. The best location depends on antenna dimensions, coil dimensions and ground loss resistance ohms, and is very non-critical. Top loading is never the best. Download program LOADCOIL in a few seconds from website below and run immediately. ---- .................................................. .......... Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.btinternet.com/~g4fgq.regp .................................................. .......... |
Buck wrote: I have aluminum poles of three diameters, 1.5, 1, and .5 inches. I have enough of the first two to create a pole of about 15 feet each and about 8 to 9 feet with the 1/5 inch poles. The poles are no more than 4 feet long each, but they are able to tuck inside each other, at least for the same diameter. What I want to do is to make up a 'kit' with these that I can take to the field to setup whatever antenna I want to use at the time. For example, I might set it up as a 20 meter vertical in one configuration, but in the evening, I might reconfigure it to 75 meters or 15, or 30 or whatever I desire. One consideration is to create a high-q coil for it. I am thinking of using 1/4 inch copper tubing to make a ten to twelve inch diameter coil so I can match it to the lower bands. That thickness of coil is overkill.... I have been reading that base loaded coils have to be matched to the antenna, but center loaded verticals are more closely matched to 50 ohms. The loading coil is used to tune out the capacitive reactance. The input impedance will vary to length of the vertical, coil loss, ground loss, etc..Just because a center load is used, doesn't always mean the input impedance will end up 50 ohms.. from what I have been reading, the center loaded coil requires more turns and a top loaded coil even more. Yes. A capacity hat is also a viable option. It's the best option. And top loading is best using capacitive loading, where as if using a coil for top loading, the coil losses overshadow any increase in efficiency from the improved current distribution, etc.. Top loading using wires is the best system you could use, if you can swing it. I am wondering how much I am helping or hurting myself with the larger coil or if I would be better off with a smaller coil. It's not that critical... One thought is to connect x number of poles, then the coil, then another set of poles or a whip to make the final adjustment for the match or to match the antenna by tapping the coil. I am open to all suggestions, but I am interested in knowing the best location for the coil and the best size for it. The *best* location for a loading coil is appx 2/3 to 3/4 up the radiator. But even half way up is fine. Base loading is the least efficient, and has the worst current distribution. But it uses the least number of coil turns, and would have the least coil loss. Being low, it's the easiest to adjust also... Don't forget that the ground system for a short loaded vertical, becomes even more critical than for a full 1/4 wave vertical. It's for this reason that I usually avoid verticals for portable use, unless the ground issue can be dealt with. IE: at the beach is a good place for verticals...But in the boonies, on lossy, rocky, ground, they may not do so hot if you have no radials. In that case, I would take the vertical "sticks", and hang a dipole from them...:/ My mobile antenna is my usual "portable vertical"...MK |
" bravely wrote to "All" (23 Mar 05 15:13:22)
--- on the heady topic of " Loading Coil Q" nm It's the best option. And top loading is best using capacitive nm loading, where as if using a coil for top loading, the coil losses nm overshadow any increase in efficiency from the improved current nm distribution, etc.. Top loading using wires is the best system you nm could use, if you can swing it. How about distributed loading? A*s*i*m*o*v .... May you find the light and walk the mountain tops. |
On Wednesday, 23 Mar 2005 22:30:32 -500, "Asimov"
wrote: How about distributed loading? Hi OM, The wrong way, and it is called air cooled resistance. If you simply did a Googles group search using that very query, you would find a trove of hits. 73's Richard Clark, KB7QHC |
Reg Edwards wrote:
Amongst other things it allows the coil to slide up and down the antenna (from the keyboard) and find the coil location at which power radiating efficiency is maximised. Sliding the coil up and down the antenna also changes the resonant frequency. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
Asimov wrote:
How about distributed loading? Helical antennas are not as efficient as other forms of loading. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
Thank you to Cecil, Reg, Mark, Asimov and Richard. I have read what you said and done more reading about Cap Hats. The Cap Hat doesn't improve the inductor, it basically replaces it, at least in part, which removes the loss of the inductor. I misunderstood that somehow. What I will focus on, then, is to create some form of capacity hat for each appropriate band together with an adjustable vertical length for tuning to the appropriate frequency. Mark, You may have a point about the dipole being better, especially for portable operation. I just want to experiment with the aluminum poles I have. I may take your advice and use them to create a portable tower in the long-run. But first I think I will try out the vertical. Thanks to all, Buck N4PGW On Wed, 23 Mar 2005 12:56:34 -0500, Buck wrote: I have aluminum poles of three diameters, 1.5, 1, and .5 inches. I have enough of the first two to create a pole of about 15 feet each and about 8 to 9 feet with the 1/5 inch poles. The poles are no more than 4 feet long each, but they are able to tuck inside each other, at least for the same diameter. What I want to do is to make up a 'kit' with these that I can take to the field to setup whatever antenna I want to use at the time. For example, I might set it up as a 20 meter vertical in one configuration, but in the evening, I might reconfigure it to 75 meters or 15, or 30 or whatever I desire. One consideration is to create a high-q coil for it. I am thinking of using 1/4 inch copper tubing to make a ten to twelve inch diameter coil so I can match it to the lower bands. I have been reading that base loaded coils have to be matched to the antenna, but center loaded verticals are more closely matched to 50 ohms. from what I have been reading, the center loaded coil requires more turns and a top loaded coil even more. A capacity hat is also a viable option. I am wondering how much I am helping or hurting myself with the larger coil or if I would be better off with a smaller coil. One thought is to connect x number of poles, then the coil, then another set of poles or a whip to make the final adjustment for the match or to match the antenna by tapping the coil. I am open to all suggestions, but I am interested in knowing the best location for the coil and the best size for it. Thank you -- 73 for now Buck N4PGW |
Mark, You may have a point about the dipole being better, especially for portable operation. I just want to experiment with the aluminum poles I have. I may take your advice and use them to create a portable tower in the long-run. But first I think I will try out the vertical. You could probably rig it up to do either, if the vertical is stout enough to support a dipole/s. I have a couple of drive on masts that I use with the fence rail masting. Two of those makes 20 ft, and a good support for dipoles, or other antennas. For industrial use, I have a tower and beam I can drag around...I've drug it to the last four field days...Wonder if I'm gonna make it five..?? It's a lot of work for a two day deal....:/ I'm almost tempted to take a field day vacation for a year...Have to see...MK |
"Cecil Moore" bravely wrote to "All" (24 Mar 05 09:19:15)
--- on the heady topic of " Loading Coil Q" CM From: Cecil Moore CM Xref: aeinews rec.radio.amateur.antenna:27211 CM Helical antennas are not as efficient as CM other forms of loading. Considering that sometimes efficiency isn't quite as important, like for example reception, are helical antennas less used simply because the math is a little harder or not discussed enough? I recall seeing this type being popularized during the old CB craze in the mid 70's. A*s*i*m*o*v .... "Ol' Frothinslosh": The pale, stale ale with the foam on the bottom. |
Asimov wrote:
"Cecil Moore" wrote: CM Helical antennas are not as efficient as CM other forms of loading. Considering that sometimes efficiency isn't quite as important, like for example reception, are helical antennas less used simply because the math is a little harder or not discussed enough? Probably a collection of reasons. A high-Q loading coil in the center of a vertical is much more efficient than spreading the loading out over the entire antenna. Helical antennas are hard to wind and are generally wound on PVC pipe which also reduces efficiency and increases wind load. Even more efficiency is lost without a good ground plane. If one doesn't compromise on the ground plane, why compromise on the antenna? Most of us old timers have tried helicals and given up on them - lots of effort to achieve a poor performance. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
"Cecil Moore" wrote A high-Q loading coil in the center of a vertical is much more efficient than spreading the loading out over the entire antenna. ============================ Wrong! Spreading a multi-turn coil allows a MUCH thicker wire diameter to be used with spaced turns. Also the coil diameter can be increased to minimise the number of turns. Result : higher coil Q, lower coil loss, greater efficiency. ---- Reg. |
Dear "Asimov" w/o a call sign:
If you look closely, you will see that the "coiled up ribbon" is a transmission line or a pair of transmission lines. By elevating the antenna, which must be connected to the truck through at least one transmission line, much improved transmission range is effected. 73 Mac N8TT -- J. Mc Laughlin; Michigan U.S.A. Home: "Asimov" wrote in message ... " bravely wrote to "All" (24 Mar 05 09:41:39) --- on the heady topic of " Loading Coil Q" snip Lately I've seen TV media trucks with a type of rather wide pole of what seems to consist of a large coiled up ribbon. When they get to a location they unfurl the tube and it raises the microwave antenna. They seem to be made out of plastic or carbon, not sure. The one I saw went up about 30 feet. It seems very lightweight in any case. Anyone here know what it is? A*s*i*m*o*v |
Reg Edwards wrote:
"Cecil Moore" wrote A high-Q loading coil in the center of a vertical is much more efficient than spreading the loading out over the entire antenna. Wrong! Spreading a multi-turn coil allows a MUCH thicker wire diameter to be used with spaced turns. Also the coil diameter can be increased to minimise the number of turns. Result : higher coil Q, lower coil loss, greater efficiency. Got to disagree with you on that one, Reg. Mobile shootout field strength measurements put all the helicals, no matter what wire diameters were used, considerably down from the well-designed bugcatchers and screwdrivers. That meter of wire in each turn of the helical has more resistance than the centimeter of radiating bottom section that it replaces at the feedpoint. It is well known and accepted that moving the mobile loading coil from the center of the antenna to the base will reduce the efficiency even though the inductance required for loading is decreased. With a helical, part of the loading coil is at the base and that's simply a bad idea when efficiency is important. One mobile, in particular, should have performed well. It was made from 1/4 inch copper tubing with a large diameter and proper spacing between turns but it was about equal to a Hustler and considerably down from the top performer which was top-loaded. What wins the mobile shootouts is the longest possible straight bottom section under the coil where the highest current occurs. That maximum current occurs all up and down that straight bottom section when a good top hat is added to the antenna. I once won the shootout competition by putting all the loading (coil+top-hat) at the top of the antenna using cheap stuff from my junk box. If one wants to win a mobile shootout, one cannot afford to install a helical coil at the maximum current section. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
"Cecil Moore" wrote in message ... Reg Edwards wrote: "Cecil Moore" wrote A high-Q loading coil in the center of a vertical is much more efficient than spreading the loading out over the entire antenna. Wrong! Spreading a multi-turn coil allows a MUCH thicker wire diameter to be used with spaced turns. Also the coil diameter can be increased to minimise the number of turns. Result : higher coil Q, lower coil loss, greater efficiency. Got to disagree with you on that one, Reg. Mobile shootout field strength measurements put all the helicals, no matter what wire diameters were used, considerably down from the well-designed bugcatchers and screwdrivers. That meter of wire in each turn of the helical has more resistance than the centimeter of radiating bottom section that it replaces at the feedpoint. It is well known and accepted that moving the mobile loading coil from the center of the antenna to the base will reduce the efficiency even though the inductance required for loading is decreased. With a helical, part of the loading coil is at the base and that's simply a bad idea when efficiency is important. One mobile, in particular, should have performed well. It was made from 1/4 inch copper tubing with a large diameter and proper spacing between turns but it was about equal to a Hustler and considerably down from the top performer which was top-loaded. What wins the mobile shootouts is the longest possible straight bottom section under the coil where the highest current occurs. That maximum current occurs all up and down that straight bottom section when a good top hat is added to the antenna. I once won the shootout competition by putting all the loading (coil+top-hat) at the top of the antenna using cheap stuff from my junk box. If one wants to win a mobile shootout, one cannot afford to install a helical coil at the maximum current section. -- ================================== Cec, (1) A mobile antenna is NOT a 1/4-wave resonant, base-fed, ground-mounted loaded vertical which behaves reasonably predictable. (2) A mobile antenna is a relatively-isolated-from-ground, 1/2-wave resonant, loaded, off-centre-fed vertical dipole which defies rational analysis. (3) It is impossible to separate the many different behaviour modes and effects, differentiate between them and allocate relative magnitudes. One has to be careful to control one's imagination when describing effects. I've never seen one near to, but I understand "screwdriver" type mobile antennas are akin to long helicals specially at the lowest operating frequency. ---- Reg. |
Reg Edwards wrote:
I've never seen one near to, but I understand "screwdriver" type mobile antennas are akin to long helicals specially at the lowest operating frequency. All of the screwdrivers with which I am familiar use a 3-6 foot straight bottom section. The 2 foot max coil is approximately in the center with a 3-6 foot whip. The coil goes in and out of the 3-6 foot bottom section for tuning. Do you subscribe to the theory that a one foot long coil radiates approximately the same RF as a one foot long piece of wire? With any reasonable diameter of coil, the resistance in that one foot long coil will be greater than the resistance in one foot of wire. For instance, the circumference of a coil may be one meter while the turn spacing may be one centimeter. What size wire do you need to compensate for that 100/1 ratio? -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
| All times are GMT +1. The time now is 08:58 PM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com