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@0 Meter Vertical Collinear
I was looking through some of my old antenna books and came across an
article from K6TS about building a 20 Meter Collinear antenna. Has anyone ever built one, or have any input on if it would be worthwhile to pursue. Weather is getting warm here, so I was looking for another antenna project. 20 meters, vertical and ground mounted. So I was thinking about 1/2 Wave, 5/8 wave or the collinear. Ken |
@0 Meter Vertical Collinear
On 24 feb, 17:45, Ken Slimmer wrote:
* I was looking through some of my old antenna books and came across an article from K6TS about building a 20 Meter Collinear antenna. *Has anyone ever built one, or have any input on if it would be worthwhile to pursue. *Weather is getting warm here, so I was looking for another antenna project. *20 meters, vertical and ground mounted. *So I was thinking about 1/2 Wave, 5/8 wave or the collinear. Ken Hello Ken, I would not use the 5/8 wave antenna, unless you can make a dipole of 1.25lambda. The 5/8 wave vertical only gives the published gain over a large good conducting ground plane. 3 or 4 quarter wave radials may provide a reasonable floating ground for feeding the antenna, but it is not a large ground plane. Using a half wave has the disadvantage of the more complicated feeding network. You may expect impedances up to kOhm range (depending in thickness of the radiating element), so you need some high voltage evaluation of your structure in case of 100W input power. The advantage is the low requirement for the (floating) ground at the feed point. Just 1 or 2 quarter wave radials are sufficient. These radial wires may also slope down, as they carry low current, hence do not have large influence on radiation pattern. When you have some metal structure around you, you can use that as ground, eliminating the need for radials. When you look to half wave CB antennas, most ones do not have radials at all. When you want to use horizontal polarization, a full wave center fed dipole or 1.25lambda center fed antenna can be nice. Of course you have to make something to rotate it…. When you want to design a vertical HW antenna from the ground up, I have a document on my website dedicated to HW end-fed antenna design. It also addresses high voltage issues. http://www.tetech.nl/divers/HWmonopoleNL1.pdf. It is in Dutch language, but all comment in illustrations and formulas is in English, so it can be helpful. Best regards, Wim PA3DJS www.tetech.nl without abc, the mail is OK. |
@0 Meter Vertical Collinear
Wim;
Thanks for your input, I just noticed that I had my finger on the shift key when I posted the subject, so it came out as @0 meter.. :-) I don't ever plan on running high power, 100 watts is about my limit. I do want to stick to putting a vertical up. I have an old 1/4 wave 40 meter vertical that I was going to scrounge parts from. Ken On Tue, 24 Feb 2009 10:19:14 -0800, wimabctel wrote: On 24 feb, 17:45, Ken Slimmer wrote: Â* I was looking through some of my old antenna books and came across Â* an article from K6TS about building a 20 Meter Collinear antenna. Â*Has anyone ever built one, or have any input on if it would be worthwhile to pursue. Â*Weather is getting warm here, so I was looking for another antenna project. Â*20 meters, vertical and ground mounted. Â*So I was thinking about 1/2 Wave, 5/8 wave or the collinear. Ken Hello Ken, I would not use the 5/8 wave antenna, unless you can make a dipole of 1.25lambda. The 5/8 wave vertical only gives the published gain over a large good conducting ground plane. 3 or 4 quarter wave radials may provide a reasonable floating ground for feeding the antenna, but it is not a large ground plane. Using a half wave has the disadvantage of the more complicated feeding network. You may expect impedances up to kOhm range (depending in thickness of the radiating element), so you need some high voltage evaluation of your structure in case of 100W input power. The advantage is the low requirement for the (floating) ground at the feed point. Just 1 or 2 quarter wave radials are sufficient. These radial wires may also slope down, as they carry low current, hence do not have large influence on radiation pattern. When you have some metal structure around you, you can use that as ground, eliminating the need for radials. When you look to half wave CB antennas, most ones do not have radials at all. When you want to use horizontal polarization, a full wave center fed dipole or 1.25lambda center fed antenna can be nice. Of course you have to make something to rotate it…. When you want to design a vertical HW antenna from the ground up, I have a document on my website dedicated to HW end-fed antenna design. It also addresses high voltage issues. http://www.tetech.nl/divers/HWmonopoleNL1.pdf. It is in Dutch language, but all comment in illustrations and formulas is in English, so it can be helpful. Best regards, Wim PA3DJS www.tetech.nl without abc, the mail is OK. |
@0 Meter Vertical Collinear
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@0 Meter Vertical Collinear
On Feb 24, 2:44*pm, Ken Slimmer wrote:
Wim; * * *Thanks for your input, I just noticed that I had my finger on the shift key when I posted the subject, so it came out as @0 meter.. *:-) * * *I don't ever plan on running high power, 100 watts is about my limit. *I do want to stick to putting a vertical up. *I have an old 1/4 wave 40 meter vertical that I was going to scrounge parts from. * If you already have a 32 ft radiator, I would go with the half wave. Feeding one is simple. I prefer the "gamma loop" type of feed. I've built many of those, and they are simple to get going, and work well. The antenna as it is does not require radials to function as a "complete" antenna. Most will work fine as is, with no radials. But if one wants to further improve one, they can be further decoupled from the feedline using decoupling sections. The way I usually decouple a base fed half wave is to use a 1/4 wave length of coax dropping down the supporting mast to a union which I clamp a set of quarter wave radials. The shield of the coax is bonded to the radial set. That will do a pretty good job of decoupling the feed line, if common mode current ends up a problem. But like I say, I've never had any problems using one with no radials. I consider the decoupling as optional. A 5/8 wave GP would be nice, but that will take a pretty tall radiator on 20m, and may be unpractical. Also, I don't use 1/4 wave radials under 5/8 verticals. This page explains my position on that issue.. http://home.comcast.net/~nm5k/acompari.htm If you want to avoid the funky high angle lobe you often see on poorly designed 5/8 wl antennas, use 5/8, or 3/4 wave radials. I've done very extensive testing of all the usual types of verticals on 10m, and the 5/8 GP is the best performer of the bunch, even with it's supposed warts. Even the 1/2 waves I used with decoupling sections were never as good as the 5/8 GP when working far off space wave stations. But like I say, a 5/8 GP on 20m could end up being a real pain to deal with. You are talking a 41 ft radiator, and that needs a supporting mast under it. Radials under it too. BTW, a 1/4 wl GP is not a bad antenna if you want to take the easy way out. Needs radials though. I haven't looked at the collinear design, but sounds like more trouble than it's worth. Would be tall too. Most higher gain collinear antennas used on 20m would probably be horizontal wire affairs. |
@0 Meter Vertical Collinear
On 25 feb, 00:10, Richard Clark wrote:
On Tue, 24 Feb 2009 10:19:14 -0800 (PST), wrote: Hello Ken, I would not use the 5/8 wave antenna, unless you can make a dipole of 1.25lambda. The 5/8 wave vertical only gives the published gain over a large good conducting ground plane. 3 or 4 quarter wave radials may provide a reasonable floating ground for feeding the antenna, but it is not a large ground plane. This and other points are deceptive. First, the performance you site is indeed due to the plane of ground (not to be confused with our usage of the term ground plane) to the extent of the conductivity of ground out about 5 to 10 wavelengths away from the antenna. No practical ground system is going to impact that. The ground system placed below the antenna WILL impact gain, only insofar as it shields the ground's loss contribution. Hence the large number of radials. Using a half wave has the disadvantage of the more complicated feeding network. You may expect impedances up to kOhm range (depending in thickness of the radiating element), so you need some high voltage evaluation of your structure in case of 100W input power. The advantage of the half wave is exactly for its high impedance in relation to the loss of ground. The far ground still dominates low angle launch characteristics, but if (like the large number of radials offers) you lose less to ground, you have more in the air in all directions. That advantage of high impedance is also the disadvantage, 1500 Ohm end-fed impedance, or higher, is not uncommon. With 400W input power, this leads to 1100Vp voltage (at 1500 Ohms). Without careful construction, E-field at sharp edges will exceed 3000V/mm easily. This will not result in full air breakdown (due to strong nun-uniformity of E-field, but will result in undesired corona discharge. The advantage is the low requirement for the (floating) ground at the feed point. Just 1 or 2 quarter wave radials are sufficient. These radial wires may also slope down, as they carry low current, hence do not have large influence on radiation pattern. If there is just 1, or if the 2 are not symmetrical, then the DO contribute to the radiation pattern lobe shape. As to the degree or notice, that is variable to the user/listener. End fed impedance for 3cm thick radiator is about 1500 Ohms, hence radiator current (middle) is about 5 times higher then feed current to the quarter wave radial. Therefore current*length product for radiator is 10 times as high as for the radial. When the radial is vertically oriented (worst case situation) influence on field from radiator is +/- 10%. So very worst case you are talking of 1dB. When the radial runs horizontally, the effect on the vertical component under low elevation angle is negligible. As the original question relates to amateur service, mentioning: "hence do not have large influence on radiation pattern" is justified, in my opinion. When you have some metal structure around you, you can use that as ground, eliminating the need for radials. When you look to half wave CB antennas, most ones do not have radials at all. They probably rely on the coax shield as a return path, which makes it notoriously unreliable in its state of tune. Mostly CB antennas are mounted on a metal mast, so part of the return current goes through the mast. You are right, in some cases this may lead to significant common mode current, but looking to my experience, this seldom resulted in untunable systems when lambda/dradiator is high. I did experience problems in antennas for VHF where thickness of radiator is no longer thin to wavelength. Fortunately, at such frequencies a simple ground is easy to make. 73's Richard Clark, KB7QHC Wim PA3DJS |
@0 Meter Vertical Collinear
On 25 feb, 09:10, wrote:
On Feb 24, 2:44*pm, Ken Slimmer wrote: Wim; * * *Thanks for your input, I just noticed that I had my finger on the shift key when I posted the subject, so it came out as @0 meter.. *:-) * * *I don't ever plan on running high power, 100 watts is about my limit. *I do want to stick to putting a vertical up. *I have an old 1/4 wave 40 meter vertical that I was going to scrounge parts from. * If you already have a 32 ft radiator, I would go with the half wave. Feeding one is simple. I prefer the "gamma loop" type of feed. I've built many of those, and they are simple to get going, and work well. The antenna as it is does not require radials to function as a "complete" antenna. Most will work fine as is, with no radials. But if one wants to further improve one, they can be further decoupled from the feedline using decoupling sections. The way I usually decouple a base fed half wave is to use a 1/4 wave length of coax dropping down the supporting mast to a union which I clamp a set of quarter wave radials. The shield of the coax is bonded to the radial set. That will do a pretty good job of decoupling the feed line, if common mode current ends up a problem. But like I say, I've never had any problems using one with no radials. I consider the decoupling as optional. A 5/8 wave GP would be nice, but that will take a pretty tall radiator on 20m, and may be unpractical. Also, I don't use 1/4 wave radials under 5/8 verticals. This page explains my position on that issue..http://home.comcast.net/~nm5k/acompari.htm If you want to avoid the funky high angle lobe you often see on poorly designed 5/8 wl antennas, use 5/8, or 3/4 wave radials. I've done very extensive testing of all the usual types of verticals on 10m, and the 5/8 GP is the best performer of the bunch, even with it's supposed warts. Even the 1/2 waves I used with decoupling sections were never as good as the 5/8 GP when working far off space wave stations. But like I say, a 5/8 GP on 20m could end up being a real pain to deal with. You are talking a 41 ft radiator, and that needs a supporting mast under it. Radials under it too. BTW, a 1/4 wl GP is not a bad antenna if you want to take the easy way out. Needs radials though. I haven't looked at the collinear design, but sounds like more trouble than it's worth. Would be tall too. Most higher gain collinear antennas used on 20m would probably be horizontal wire affairs. Nice simulations, and nice results also! Best regards, Wim PA3DJS www.tetech.nl the mail is ok when you remove abc. |
@0 Meter Vertical Collinear
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@0 Meter Vertical Collinear
Jim Lux wrote:
breakdown? Is there some distinction to "full?") One often makes a distinction between a corona discharge which exists as a steady state sort of thing and the streamers which precede a "spark". Both are air breakdown phenomena, but qualitatively different, and both are different from a low pressure discharge like that found in a fluorescent lamp or neon bulb, or from phenomena like St Elmo's Fire. . . . Most interesting. I've always thought that St. Elmo's fire was a corona discharge, and a quick web search indicates that it's apparently a very widely held misconception. What's the difference? Roy Lewallen, W7EL |
@0 Meter Vertical Collinear
On 26 feb, 02:09, Roy Lewallen wrote:
Jim Lux wrote: breakdown? *Is there some distinction to "full?") One often makes a distinction between a corona discharge which exists as a steady state sort of thing and the streamers which precede a "spark". *Both are air breakdown phenomena, but qualitatively different, and both are different from a low pressure discharge like that found in a fluorescent lamp or neon bulb, or from phenomena like St Elmo's Fire. * . . . Most interesting. I've always thought that St. Elmo's fire was a corona discharge, and a quick web search indicates that it's apparently a very widely held misconception. What's the difference? Roy Lewallen, W7EL Hello Richard, A "full air" breakdown is the situation where there is a full conducting path between the two conductors through air. So the current that goes into the conductors is mainly supported by real electron flow through air and not dielectric displacement current. The effect is strongly non-linear and shows hysteresis. Imagine you have an antenna and you increase the input power gradually. At a certain point somewhere in the construction air will break down. When you have a full breakdown in a uniform field, you will notice a stepwise change in SWR. To stop the breakdown, you have to reduce the input power significantly (hysteresis effect). As most amateurs have an in line SWR indicator, you will notice full air breakdown and will check the installation. In an RF "corona discharge", air only breaks down in the high field strength area. As you will probably know, field strength is highest at air/conductor boundary with small curvature (edges, needle tips). Outside that area air will not break down and current in that region is supported by displacement current. This effect may show only minor hysteresis and you may not notice this during normal operation. The voltage required to establish a corona discharge may be far below the level to get a full air breakdown. At the tips of a HW radiator, you will have highest field strength. However when you bring a conductor close to that tip (and retune if required), field strength will increase. This is also the case with HW end-fed radiators. At least the ground of your feeder, or the ground of the matching network will be relative close to the end of the HW resonator. For some formulas see the document referenced before. I hope this clarifies the "full air breakdown" and "corona discharge" issue as used in my postings. Best regards, Wim PA3DJS www.tetech.nl the address is still valid, but don't forget to remove abc. |
@0 Meter Vertical Collinear
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@0 Meter Vertical Collinear
Roy Lewallen wrote:
Jim Lux wrote: breakdown? Is there some distinction to "full?") One often makes a distinction between a corona discharge which exists as a steady state sort of thing and the streamers which precede a "spark". Both are air breakdown phenomena, but qualitatively different, and both are different from a low pressure discharge like that found in a fluorescent lamp or neon bulb, or from phenomena like St Elmo's Fire. . . . Most interesting. I've always thought that St. Elmo's fire was a corona discharge, and a quick web search indicates that it's apparently a very widely held misconception. What's the difference? Roy Lewallen, W7EL Indeed.. but St. Elmos fire has many characteristics not shared with corona.. (the extent of the glow, for one.. corona tends to be a very small sheath or longer leaders/fingers) Most likely, it's glow discharge off small water droplets shed from the surface from which is charged. Basically the process is like an electrostatic sprayer.. small bumps in the liquid surface form from whatever cause, and the surface charge tends to make the droplets come off. They're charged to the maximum charge for the diameter, and as the droplet evaporates, it gets smaller, causing the glow discharge to shed charge. Or, a big droplet splits into smaller droplets because of electrostatic forces. You can set up a nice demo in a dark lab with something like a cork wet with sal****er, a HV power supply, and some cookie sheets for electrodes. |
@0 Meter Vertical Collinear
Jim Lux wrote:
Most likely, it's glow discharge off small water droplets shed from the surface from which is charged. Basically the process is like an electrostatic sprayer.. One very foggy night on Hwy 1 between Carmel and Santa Cruz, I came up behind a mobile radio in operation. The glow off the end of the antenna was bright orange. An oncoming CHP officer stopped the vehicle for having a "red light" visible from the front of the vehicle. When I left the scene, the two were arguing whether it was really a "red light" and whether the operator deserved a ticket or not. I don't know what radio service was involved. -- 73, Cecil http://www.w5dxp.com "Government 'help' to business is just as disastrous as government persecution..." Ayn Rand |
20 Meter Vertical Collinear
Cecil Moore wrote:
One very foggy night on Hwy 1 between Carmel and Santa Cruz, I came up behind a mobile radio in operation. The glow off the end of the antenna was bright orange. An oncoming CHP officer stopped the vehicle for having a "red light" visible from the front of the vehicle. When I left the scene, the two were arguing whether it was really a "red light" and whether the operator deserved a ticket or not. I don't know what radio service was involved. I've read that W6AM used to drive the route between Long Beach and San Francisco. His mobile station is legendary around here. The operator was no doubt explaining to the officer that a glow discharge in air is more of a salmon than a red. Did the officer look like Broderick Crawford by any chance? :-) I couldn't help but fix the subject line. ac6xg |
@0 Meter Vertical Collinear
On Thu, 05 Mar 2009 08:11:33 -0800, Jim Kelley wrote:
Cecil Moore wrote: One very foggy night on Hwy 1 between Carmel and Santa Cruz, I came up behind a mobile radio in operation. The glow off the end of the antenna was bright orange. An oncoming CHP officer stopped the vehicle for having a "red light" visible from the front of the vehicle. When I left the scene, the two were arguing whether it was really a "red light" and whether the operator deserved a ticket or not. I don't know what radio service was involved. I've read that W6AM used to drive the route between Long Beach and San Francisco. His mobile station is legendary around here. The operator was no doubt explaining to the officer that a glow discharge in air is more of a salmon than a red. Did the officer look like Broderick Crawford by any chance? :-) I couldn't help but fix the subject line. ac6xg Rumor has it that W6AM had a 1 KW Swan amp in his trunk. Plus some really big Rhombics. -- 73's Ken Slimmer, WA0SBU |
@0 Meter Vertical Collinear
Ken Slimmer wrote:
Rumor has it that W6AM had a 1 KW Swan amp in his trunk. Plus some really big Rhombics. I wholeheartedly recommend reading his biography "Don C. Wallace: Amateur Radio's Pioneer" by Jan David Perkins. 73, ac6xg |
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