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Which is better: 5/8 wave vertical or J pole?
Which antenna is better: 5/8 wavelength vertical or a J pole? Frequency of operation is 145 MHz = 2 metres. The 5/8 wavelength vertical has a loading coil. There are losses in the coil. The J pole has a quarterwave matching stub. The matching stub provides an out of phase current which means that there is a cancelling field close to the radiating element. Also the J pole is end fed, which means the transmitter is not connected directly to a maximum current point. Does the J pole have a disadvantage because of the cancelling field from the matching stub and the fact that it is end fed? Also consider gain and angle of radiation. |
Which is better: 5/8 wave vertical or J pole?
"David" nospam@nospam wrote in
: Which antenna is better: 5/8 wavelength vertical or a J pole? Better for what? For example, a 5/8 whip would usually be better than a J Pole for mobile applications on a car roof, but that doesn't make it better for all applications. Frequency of operation is 145 MHz = 2 metres. The 5/8 wavelength vertical has a loading coil. There are losses in the coil. It is certainly popular to talk down an antenna with loading coils or traps because they are "lossy". Everthing in a real world antenna has loss, the issue is the magnitude of the loss, and the impact of that on system performance for the intended application. You might find it hard to believe that some antenna systems incorporate loss elements in order to reduce feed line loss by more than that in the introduced elements. Whilst you have chosen to raise the loss in the coil, you haven't raised the issue that a J Pole has currents flowing in lossy conductors, components of which that do not directly contribute to radiation. The J pole has a quarterwave matching stub. The matching stub provides an out of phase current which means that there is a cancelling field close to the radiating element. Also the J pole is end fed, which This is not a very good way of analysing the J Pole. The U section can be thought of as carrying currents that have differential and common mode components. The common mode components contribute directly to radiation field. You should also consider common mode current on the supporting structure and feedline. The 5/8 wave vertical also has potential for significant common mode current on the supporting structure and feedline, you need to look at the effectiveness of the decoupling method employed (usually a radial set). means the transmitter is not connected directly to a maximum current point. What does that matter? BTW, neither is the base fed 5/8. There is a maxim in ham radio that antennas should always be fed at a current maximum. You could subscribe to that, but you would limit yourself by excluding a range of good solutions, and with no guarantee that a current fed antenna is optimum. Does the J pole have a disadvantage because of the cancelling field There is not perfect cancellation at all points on the U section. from the matching stub and the fact that it is end fed? "End fed", as opposed to a centre fed dipole perhaps. But isn't the 5/8 "end fed"? Also consider gain and angle of radiation. The three dimensional gain distribution is important, but dependent on the common mode issue mentioned above (amongst other things). It is fair to say that J Poles are very popular, and that they are overly represented in problems discussed in online fora. On the other hand, the 5/8 which was once very popular for mobile work in this area, is long lost, replaced by two, three and four band antennas where VSWR is more important than any other performance parameters. I use a 5/8 vertical on my car, and regularly work repeaters mobile at distances well over 100km. The antenna is more than thirty years old, and has never required repair despite hitting low trees, carpark roofs etc lots of times. The modern multiband antennas are not that robust. I wouldn't even think of a J Pole in this application. So, "best" can be a quite complex requirement. Owen |
Which is better: 5/8 wave vertical or J pole?
On Nov 7, 1:08*pm, "David" nospam@nospam wrote:
Which antenna is better: 5/8 wavelength vertical or a J pole? Frequency of operation is 145 MHz *= 2 metres. The 5/8 wavelength vertical has a loading coil. There are losses in the coil. The J pole has a quarterwave matching stub. The matching stub provides an out of phase current which means that there is a cancelling field close to the radiating element. Also the J pole is end fed, which means the transmitter is not connected directly to a maximum current point. Does the J pole have a disadvantage because of *the cancelling field from the matching stub and the fact that it is end fed? Also consider gain and angle of radiation. They are both "problem" antennas.. The usual 5/8 GP is a problem antenna because years ago some designer decided to use 1/4 wave radials instead of 5/8 or even 3/4 wave. And most ignore common mode issues. The J Pole often suffers because most tend to ignore common mode issues, which leads back to lame incomplete antenna design. :/ Both can be greatly helped by adding decoupling sections at and below the feed point. The 5/8 antenna should be run as a collinear with dual 5/8 elements. And with a lower decoupling section. The dual 5/8 collinear is more effective than any half wave vertical, even if the half wave is decoupled from the feed line. BTW, I have no real issues feeding from a high voltage point. And the loss in a 5/8 loading coil is probably not enough to even measure for most people. Both are non issues. The real issue is lack of decoupling, and using a perverted 5/8 over 1/4 wave element scheme in the case of the usual 5/8 ground plane. The perverted antenna design actually ruins the pattern of what would be a decent antenna if it were designed correctly with dual 5/8 elements. Even running 3/4 wave sloping radials is much better than using the usual 1/4 wave radials. Of course, mobile 5/8 whips are only the upper half of the antenna. They don't supply the lower half in that case. For those, the vehicle is the lower part of the antenna and performance can vary from good to horrible depending on where it's mounted. |
Which is better: 5/8 wave vertical or J pole?
Which is better?
As already said, just depends on what you are looking for. One thing about these two antennas is that one is a 1/2 wave, the other a 5/8 wave. They have different radiation patterns/characteristic. So, which of those characteristics would 'fit' your requirements the best? That's the one that's best for -your- situation. - 'Doc |
Which is better: 5/8 wave vertical or J pole?
"David" nospam@nospam wrote in message ... Which antenna is better: 5/8 wavelength vertical or a J pole? Frequency of operation is 145 MHz = 2 metres. The 5/8 wavelength vertical has a loading coil. There are losses in the coil. The J pole has a quarterwave matching stub. The matching stub provides an out of phase current which means that there is a cancelling field close to the radiating element. Also the J pole is end fed, which means the transmitter is not connected directly to a maximum current point. Does the J pole have a disadvantage because of the cancelling field from the matching stub and the fact that it is end fed? Also consider gain and angle of radiation. I'm currently building a 5/8 wave ground plan for 2mx as a tower based antenna, I have used J pole and slim jim type antennas in the past for the same purpose with success. I would think that the 5/8 radiator may have slight gain advantage, but believe that the J pole may have a slightly lower angle of radiation. The J pole is certainly easier to construct as there is a bit of mucking about with 1/8wave loading coil on the 5/8 antenna. There has been much discussion about common mode currents produced on the feed line for the J pole that can create an unpredictable radiation pattern which is partly why I'm constructing the 5/8 and partly I'm building a 5/8 ground plan as I have never built one before. Build both and compare. If the antenna is for mobile I would certainly use the 5/8 antenna. -- Peter VK6YSF http://members.optushome.com.au/vk6ysf/vk6ysf/main.htm |
Which is better: 5/8 wave vertical or J pole?
"David" nospam@nospam wrote in message ... Which antenna is better: 5/8 wavelength vertical or a J pole? Frequency of operation is 145 MHz = 2 metres. The 5/8 wavelength vertical has a loading coil. There are losses in the coil. The J pole has a quarterwave matching stub. The matching stub provides an out of phase current which means that there is a cancelling field close to the radiating element. Also the J pole is end fed, which means the transmitter is not connected directly to a maximum current point. Does the J pole have a disadvantage because of the cancelling field from the matching stub and the fact that it is end fed? Also consider gain and angle of radiation. I would not say any of the simple veticals are better. While I have not tried them from fixed locations, expirimenting with several differant mobile antennas over the years it seems that one type is not really that much beter than another. Depending on the direction and height of the repeaters almost any antenna can be better going into one repeater and worse going to another. Several of us got together and put several antennas (one at a time) on the same mount of a car. Depending on the particular repeater, there was not one overall winner. The car also had a 40 meter loaded whip that we tried and it was actually better into some of the repeaters. About the only antenna overall not suited was a colinear about 6 feet long. It worked well enough while parked, but at highway speeds it whipped around so much the mobile flutter made it almost unusable. |
Which is better: 5/8 wave vertical or J pole?
"Peter" wrote in
. au: .... construct as there is a bit of mucking about with 1/8wave loading coil on the 5/8 antenna. Why do you call it a 1/8 wave loading coil? It wouldn't be along the lines of the flawed "loading coil replaces the missing degrees" concept would it? A 5/8 monopole's performance is quite senstive to the ground plane implementation. The behavior of a 5/8 monopole over a perfect ground is not replicated over real radial systems or car roofs, yet people compare antennas based on the perfect ground plane environment. As the length of the radiator is increased beyone a half wave, low angle gain increaeses until about 0.6 wavelengths when power is shifted into a developing upper lobe. The optimum length over a perfect ground is probably just a little less than 5/8, and less still over practical ground planes. The other dimension is feedpoint impedance. For a simple series L matching arrangement, R is a little high and the optimum length is typically longer than 5/8. So, for optimum pattern, and low VSWR, a better solution is a tapped base coil with 0.6 wavelength vertical... but that doesn't play well with the simplest of mobile antenna bases that provide only one connection to the screw on antenna. Owen |
Which is better: 5/8 wave vertical or J pole?
On Nov 9, 3:02*pm, Owen Duffy wrote:
Why do you call it a 1/8 wave loading coil? It wouldn't be along the lines of the flawed "loading coil replaces the missing degrees" concept would it? Of course, the loading coil doesn't replace all of the missing degrees, but it does replace some of the missing degrees. The following inductance calculator will give the Z0 and axial propagation factor of a coil from which the VF of the coil can be calculated. When one knows the Z0 and VF of the coil, it can simply be treated as a transmission line. http://hamwaves.com/antennas/inductance.html It is obvious that the loading coil at the bottom of a 5/8WL antenna somehow causes the antenna to be electrically 3/4WL (270 degrees) long because that's the only way the reflected wave can arrive back at the feedpoint in phase with the forward wave in order to give a resistive feedpoint impedance. So we need to answer the question of exactly where those delays and phase shifts occur. Here's a conceptual model of the 5/8WL base-loaded antenna. (The 50 ohm tapped point on the coil has been ignored to simplify the problem.) FP-//////////-----------5/8WL------------------- (1) The coil occupies a certain number of degrees of the antenna. (2) Since the Z0 of the coil and the Z0 of the whip are different, there is a phase shift at the junction of the coil and the whip that can be easily calculated. (3) The 5/8WL whip obviously occupies 225 degrees of the antenna. All we have to do is figure out what the phase shift is at the coil/whip junction and how many degrees the coil occupies. degrees of coil = 270 - 225 - coil/whip phase shift There's no magical faster-than-light propagation through the coil as predicted by the lumped-circuit model. Coils are known to cause a delay and the Hamwaves inductance calculator provides us an easy way of calculating that delay through the loading coil. I can provide an example if necessary. -- 73, Cecil, w5dxp.com |
Which is better: 5/8 wave vertical or J pole?
On Nov 9, 6:39*pm, Cecil Moore wrote:
... the Hamwaves inductance calculator provides us an easy way of calculating that delay through the loading coil. http://hamwaves.com/antennas/inductance.html Assume a 10" long, 100 turn coil with a diameter of 2" wound with #18 wire. In metric, that's 254 mm long, 50.8 mm diameter, and 1.024 mm wire. At 4 MHz, the above calculator indicates that the axial propagation factor is 2.122 rad/m which we can convert to degrees/inch by multiplying by 1.4554 which yields 3.088 degrees per inch. The coil is 10 inches long so the number of degrees occupied by the coil at 4 MHz is 30.9 degrees. If this coil is used as a base loading coil in a 4 MHz mobile antenna, it occupies ~30.9 degrees of the antenna. A 7 foot whip occupies ~10.2 degrees at 4 MHz. The antenna, at resonance, is known to be 90 degrees long. So the phase shift at the coil to whip junction has to be ~48.9 degrees assuming resonance at 4 MHz. For an electrical 1/4WL base-loaded antenna, e.g. an HF mobile antenna, there exist three phase shifts that add up to 90 degrees. The phase shift through the coil plus the coil to whip junction phase shift plus the phase shift through the whip have to add up to 90 degrees. For a center-loaded antenna, there are four phase shifts that must add up to 90 degrees. The phase shift at the base to bottom of loading coil junction is negative. That's why we need more inductance, i.e. more phase shift, in the center-loading coil than we do in the base loading coil. If we are dealing with a 5/8WL (225 deg) antenna, the phase shift through the base coil plus the phase shift at the coil to whip junction must add up to 45 degrees such that 225 deg + 45 deg = 270 deg = 6/8WL. -- 73, Cecil, w5dxp.com |
Which is better: 5/8 wave vertical or J pole?
On Nov 7, 4:18*pm, Owen Duffy wrote:
"David" nospam@nospam wrote : Which antenna is better: 5/8 wavelength vertical or a J pole? Better for what? For example, a 5/8 whip would usually be better than a J Pole for mobile applications on a car roof, but that doesn't make it better for all applications. Frequency of operation is 145 MHz *= 2 metres. The 5/8 wavelength vertical has a loading coil. There are losses in the coil. It is certainly popular to talk down an antenna with loading coils or traps because they are "lossy". Everthing in a real world antenna has loss, the issue is the magnitude of the loss, and the impact of that on system performance for the intended application. You might find it hard to believe that some antenna systems incorporate loss elements in order to reduce feed line loss by more than that in the introduced elements. Whilst you have chosen to raise the loss in the coil, you haven't raised the issue that a J Pole has currents flowing in lossy conductors, components of which that do not directly contribute to radiation. The J pole has a quarterwave matching stub. The matching stub provides an out of phase current which means that there is a cancelling field close to the radiating element. Also the J pole is end fed, which This is not a very good way of analysing the J Pole. The U section can be thought of as carrying currents that have differential and common mode components. The common mode components contribute directly to radiation field. You should also consider common mode current on the supporting structure and feedline. The 5/8 wave vertical also has potential for significant common mode current on the supporting structure and feedline, you need to look at the effectiveness of the decoupling method employed (usually a radial set). means the transmitter is not connected directly to a maximum current point. What does that matter? BTW, neither is the base fed 5/8. There is a maxim in ham radio that antennas should always be fed at a current maximum. You could subscribe to that, but you would limit yourself by excluding a range of good solutions, and with no guarantee that a current fed antenna is optimum. Does the J pole have a disadvantage because of *the cancelling field There is not perfect cancellation at all points on the U section. from the matching stub and the fact that it is end fed? "End fed", as opposed to a centre fed dipole perhaps. But isn't the 5/8 "end fed"? Also consider gain and angle of radiation. The three dimensional gain distribution is important, but dependent on the common mode issue mentioned above (amongst other things). It is fair to say that J Poles are very popular, and that they are overly represented in problems discussed in online fora. On the other hand, the 5/8 which was once very popular for mobile work in this area, is long lost, replaced by two, three and four band antennas where VSWR is more important than any other performance parameters. I use a 5/8 vertical on my car, and regularly work repeaters mobile at distances well over 100km. The antenna is more than thirty years old, and has never required repair despite hitting low trees, carpark roofs etc lots of times. The modern multiband antennas are not that robust. I wouldn't even think of a J Pole in this application. So, "best" can be a quite complex requirement. Owen Owen, I think the popularity of VHF mobile 5/8 antenna lies in it has more gain than a 1/4 wl antenna and is easier to match to 50 ohms than a .5 wl antenna. I had certainly rather DIY a 2M 5/8 mobile antenna than a .5 wl version. From information I have seen the 5/8 often touted for its low angle of radiation may actually have a significantly higher angle of radiation than the .5 wl antenna used in a similar situation. This is not to say either antenna would not be equally useful. Jimmie |
Which is better: 5/8 wave vertical or J pole?
On Nov 10, 3:46*pm, JIMMIE wrote:
On Nov 7, 4:18*pm, Owen Duffy wrote: "David" nospam@nospam wrote : Which antenna is better: 5/8 wavelength vertical or a J pole? Better for what? For example, a 5/8 whip would usually be better than a J Pole for mobile applications on a car roof, but that doesn't make it better for all applications. Frequency of operation is 145 MHz *= 2 metres. The 5/8 wavelength vertical has a loading coil. There are losses in the coil. It is certainly popular to talk down an antenna with loading coils or traps because they are "lossy". Everthing in a real world antenna has loss, the issue is the magnitude of the loss, and the impact of that on system performance for the intended application. You might find it hard to believe that some antenna systems incorporate loss elements in order to reduce feed line loss by more than that in the introduced elements. Whilst you have chosen to raise the loss in the coil, you haven't raised the issue that a J Pole has currents flowing in lossy conductors, components of which that do not directly contribute to radiation. The J pole has a quarterwave matching stub. The matching stub provides an out of phase current which means that there is a cancelling field close to the radiating element. Also the J pole is end fed, which This is not a very good way of analysing the J Pole. The U section can be thought of as carrying currents that have differential and common mode components. The common mode components contribute directly to radiation field. You should also consider common mode current on the supporting structure and feedline. The 5/8 wave vertical also has potential for significant common mode current on the supporting structure and feedline, you need to look at the effectiveness of the decoupling method employed (usually a radial set). means the transmitter is not connected directly to a maximum current point. What does that matter? BTW, neither is the base fed 5/8. There is a maxim in ham radio that antennas should always be fed at a current maximum. You could subscribe to that, but you would limit yourself by excluding a range of good solutions, and with no guarantee that a current fed antenna is optimum. Does the J pole have a disadvantage because of *the cancelling field There is not perfect cancellation at all points on the U section. from the matching stub and the fact that it is end fed? "End fed", as opposed to a centre fed dipole perhaps. But isn't the 5/8 "end fed"? Also consider gain and angle of radiation. The three dimensional gain distribution is important, but dependent on the common mode issue mentioned above (amongst other things). It is fair to say that J Poles are very popular, and that they are overly represented in problems discussed in online fora. On the other hand, the 5/8 which was once very popular for mobile work in this area, is long lost, replaced by two, three and four band antennas where VSWR is more important than any other performance parameters. I use a 5/8 vertical on my car, and regularly work repeaters mobile at distances well over 100km. The antenna is more than thirty years old, and has never required repair despite hitting low trees, carpark roofs etc lots of times. The modern multiband antennas are not that robust. I wouldn't even think of a J Pole in this application. So, "best" can be a quite complex requirement. Owen Owen, I think the popularity of VHF mobile 5/8 antenna lies in it has more gain than a 1/4 wl antenna and is easier to match to 50 ohms than a .5 wl antenna. I had certainly rather DIY a 2M 5/8 mobile antenna than a .5 wl version. From information I have seen the 5/8 often touted for its low angle of radiation may actually have a significantly higher angle of radiation than the .5 wl antenna used in a similar situation. This is not to say either antenna would not be equally useful. Jimmie It depends on the vehicle and mount location. I think often a vehicle provides a better lower section than the usual ground plane with 1/4 WL elements. I've seen 5/8 whips do quite well on vehicles if they are mounted in a good location, the best being the center of the roof. They beat 1/4 WL whips in comparison tests, and often showed less "picket fencing". I imagine a 1/2 wave would work well, but I've never actually tried a 1/2 wave whip on a vehicle due to it generally being more complex to build and match. And in the end, I think the 5/8 would probably beat it anyway. But in another comparison on 10m, the elevated 5/8 GP's beat the elevated 1/2 wave's I tried. And all were decoupled from the feed line. The comparisons were done locally, using the space/ground wave which is low angle critical, and the 5/8's always won to stations that were 30-40 miles away vs the 1/2 wave's. Anyway, I'm not nearly as negative about 5/8 wave antennas as many people are. But like I say, I think the 5/8 over 1/4 wave GP scheme is perverted and can be greatly improved using more sane designs. :/ The maximum gain for a single element is .64 wave. And that gain is usually considered appx 3 db better than a 1/4 wave. But if I remember right, the dual 5/8 collinear is usually rated at about 3 db better than a vertical 1/2 wave. "appx 5.1 dbi". For VHF/UHF use, the old AEA Isopoles were one of the best commercial verticals built as far as gain and decoupling of the feed line. Those were dual 5/8 designs with lower decoupling cones. It was the superior decoupling that really made them shine at low angles. |
Which is better: 5/8 wave vertical or J pole?
On Wed, 10 Nov 2010 13:46:12 -0800 (PST), JIMMIE
wrote: On Nov 7, 4:18*pm, Owen Duffy wrote: "David" nospam@nospam wrote : Which antenna is better: 5/8 wavelength vertical or a J pole? Better for what? For example, a 5/8 whip would usually be better than a J snip Owen, I think the popularity of VHF mobile 5/8 antenna lies in it has more gain than a 1/4 wl antenna and is easier to match to 50 ohms than a .5 wl antenna. I had certainly rather DIY a 2M 5/8 mobile antenna than a .5 wl version. From information I have seen the 5/8 often touted for its low angle of radiation may actually have a significantly higher angle of radiation than the .5 wl antenna used in a similar situation. This is not to say either antenna would not be equally useful. Jimmie In the late 1970's my work car was a tiny Ford Fiesta (AKA "Fiasco" It was fitted with a 5/8 wave on a fender mount. The transciever was a Heath 2036 at 5 watts. The antenna did perform very well as far as distance was concerned. However, it was tall enough to ping the light fixtures in the many parking garages that were essential to my job. The biggest advantage of a J-Pole is that it is not dependent on a good ground. John Ferrell W8CCW |
Which is better: 5/8 wave vertical or J pole?
On Nov 11, 11:42*am, John Ferrell wrote:
On Wed, 10 Nov 2010 13:46:12 -0800 (PST), JIMMIE wrote: On Nov 7, 4:18*pm, Owen Duffy wrote: "David" nospam@nospam wrote : Which antenna is better: 5/8 wavelength vertical or a J pole? Better for what? For example, a 5/8 whip would usually be better than a J snip Owen, I think the popularity of VHF mobile 5/8 antenna lies in it has more gain than a 1/4 wl antenna and is easier to match to 50 ohms than a .5 wl antenna. I had certainly rather DIY a 2M 5/8 mobile antenna than a .5 wl version. From information I have seen the 5/8 often touted for its low angle of radiation may actually have a significantly higher angle of radiation than the .5 wl antenna used in a similar situation. This is not to say either antenna would not be equally useful. Jimmie In the late 1970's my work car was a tiny Ford Fiesta (AKA "Fiasco" It was fitted with a 5/8 wave on a fender mount. The transciever was a Heath 2036 at 5 watts. The antenna did perform very well as far as distance was concerned. However, it was tall enough to ping the light fixtures in the many parking garages that were essential to my job. The biggest advantage of a J-Pole is that it is not dependent on a good ground. John Ferrell W8CCW I ve had both .5 and .64 wl antennas on my big Chevy Van. I cant tell any significant difference in performance except for a couple of .5 antennas that were really poor performers, I think this may have been due to matching network design.. Except for this cause I dont see how there could be any perceptable difference in the two antennas short of careful measurements on an antenna range.. Jimmie |
Which is better: 5/8 wave vertical or J pole?
On Thu, 11 Nov 2010 14:08:39 -0800 (PST), JIMMIE
wrote: In the late 1970's my work car was a tiny Ford Fiesta (AKA "Fiasco" It was fitted with a 5/8 wave on a fender mount. The transciever was a Heath 2036 at 5 watts. The antenna did perform very well as far as distance was concerned. However, it was tall enough to ping the light fixtures in the many parking garages that were essential to my job. The biggest advantage of a J-Pole is that it is not dependent on a good ground. John Ferrell W8CCW I ve had both .5 and .64 wl antennas on my big Chevy Van. I cant tell any significant difference in performance except for a couple of .5 antennas that were really poor performers, I think this may have been due to matching network design.. Except for this cause I dont see how there could be any perceptable difference in the two antennas short of careful measurements on an antenna range.. Jimmie After I could not stand the Fiesta any longer I ordered a new Cadillac Cimarron. I did not want to drill any holes in the new Caddy so I bought one of the thru the glass end fed whips. Its performance was OK and it did not draw attention to the vehicle so I lived with it. 130,000 miles later it went to our son radio, antenna and all! It only made sense when he was licensed. If I were doing it again I would have drilled the appropriated hole in the roof above the dome light and installed a Larsen 2m & 400 antenna. That was the last time I hesitated about drilling a hole where I needed it. Now that I am in a 2008 Chrysler Minivan I have taken the lazy way out and placed a mag mount quarter wave on the luggage rack (no scratching there) with the coax ty-wrapped to the rack so there is not enough slack to allow real damage if it gets knocked off. An itty-bitty Yaesu FT-90 sits on a sticky pad on the dash and plugs into one of the vehicles many12v power outlets. The power outlets are not like the cigarette lighters of the past. They are well installed and fused at 20 amps. As long as you purchase a plug to handle the power and trim the cable to what is necessary all is well. The FT-90 gets too hot to handle and shuts down on lengthy rag chews at full power, but does fine at lower power settings. You can waste a lot of time and money over killing a mobile antenna for repeater operation. If you are out in the wide open spaces, maybe it is worth it! John Ferrell W8CCW |
Which is better: 5/8 wave vertical or J pole?
Why do you call it a 1/8 wave loading coil? It wouldn't be along the lines of the flawed "loading coil replaces the missing degrees" concept would it? I referred to the 1/8 wave loading coil without really thinking about it. I was unsure of the loading coil dimensions, so I simple tried a 1/8 wave length wire formed into a coil. This is for the simple series arrangement 5/8 radiator. This created a load coil that appeared to have a little too much L so I have removed one turn, seems to load up ok after a little trimming of the radiator. Keen to hear how too determine the value/dimensions for the loading coil. Having said that I'm not sure what so wrong with missing degrees" concept. A 5/8 monopole's performance is quite senstive to the ground plane implementation. The behavior of a 5/8 monopole over a perfect ground is not replicated over real radial systems or car roofs, yet people compare antennas based on the perfect ground plane environment. As the length of the radiator is increased beyone a half wave, low angle gain increaeses until about 0.6 wavelengths when power is shifted into a developing upper lobe. The optimum length over a perfect ground is probably just a little less than 5/8, and less still over practical ground planes. The other dimension is feedpoint impedance. For a simple series L matching arrangement, R is a little high and the optimum length is typically longer than 5/8. So, for optimum pattern, and low VSWR, a better solution is a tapped base coil with 0.6 wavelength vertical... but that doesn't play well with the simplest of mobile antenna bases that provide only one connection to the screw on antenna. My current 5/8 wave ground plan project is simply to get something on air, however I plans to construct an improved version with the tapped coil approach. I may be looking in the wrong places, but I have been surprised at how little information there is on the net regarding 5/8 wave ground plan. Thanks Owen for the above over view of the 5/8 wave ground plan. Cheers Peter VK6YSF http://members.optushome.com.au/vk6ysf/vk6ysf/main.htm |
Which is better: 5/8 wave vertical or J pole?
On Nov 13, 7:11*pm, "Peter" wrote:
Having said that I'm not sure what so wrong with missing degrees" concept.. :-) Because there are two sides of the argument each at the two extremes. The technical truth is that the coil does replace a certain number of degrees of the missing part of the antenna but not all of the missing degrees. I am preparing a technical article that explains the details. Please stand by. -- 73, Cecil, w5dxp.com |
Which is better: 5/8 wave vertical or J pole?
On Sun, 14 Nov 2010 09:11:22 +0800, "Peter" wrote:
Having said that I'm not sure what so wrong with missing degrees" concept. Hi Peter, Drives some up the wall. Your terming it as a concept is perfect, but it will still be argued for being a corrupt teaching of a literal equivalence. 73's Richard Clark, KB7QHC |
Which is better: 5/8 wave vertical or J pole?
"Peter" wrote in
: .... I referred to the 1/8 wave loading coil without really thinking about it. I was unsure of the loading coil dimensions, so I simple tried a 1/8 wave length wire formed into a coil. This is for the simple series arrangement 5/8 radiator. This created a load coil that appeared to have a little too much L so I have removed one turn, seems to load up ok after a little trimming of the radiator. Keen to hear how too determine the value/dimensions for the loading coil. Hi Peter, One theoretical method is to model the antenna, and find the feedpoint impedance. The R component decreases as length increases from a half wave to three quarter wave, and X increases towards zero. Best pattern is closer to a half wave, but R is very high. At 0.7 wavelengths, R is low enough for an acceptable match by using a series inductor, and reactance will be a few hundred ohms give or take depending on length. Having said that I'm not sure what so wrong with missing degrees" concept. For one thing, if a certain inductance is required, the quantity of wire needed depends on several underlying coil parameters. .... My current 5/8 wave ground plan project is simply to get something on air, however I plans to construct an improved version with the tapped coil approach. That lets you shorten it for a bit more gain, and a good match. If you cut the vertical for 0.6 wavelengths, you should think of starting with an inductor with reactance towards 1000 ohms. I may be looking in the wrong places, but I have been surprised at how little information there is on the net regarding 5/8 wave ground plan. Probably displaced by OTS 4 band verticals. Have fun. Owen |
Which is better: 5/8 wave vertical or J pole?
Owen Duffy wrote in
: "Peter" wrote in : .... My current 5/8 wave ground plan project is simply to get something on air, however I plans to construct an improved version with the tapped coil approach. That lets you shorten it for a bit more gain, and a good match. If you cut the vertical for 0.6 wavelengths, you should think of starting with an inductor with reactance towards 1000 ohms. I meant to elaborate on this a bit more. (Did I hear someone groan?) If for example, the feedpoint Z of a 0.6 wave vertical over four quarter wave radials was 150-j500, your tapped coil matching network can be designed using bulk standard circuit theory to transform 150-j500 to 50 +j0, and nowhere do you use the missing 54° in those calcs. That might suggest that the "missing degrees" are some kind of explanatory crutch (or ham speak) that is not directly related to solving the problem. Owen |
Which is better: 5/8 wave vertical or J pole?
On Sun, 14 Nov 2010 02:25:50 GMT, Owen Duffy wrote:
I meant to elaborate on this a bit more. (Did I hear someone groan?) If for example, the feedpoint Z of a 0.6 wave vertical over four quarter wave radials... I'll bite (or groan as the expectation demands) - why "quarter wave" radials? A rule of thumb? * * * Rhetorical questions follow * * * * Quarter wave in physical length? Quarter wave in electrical length? Elevated Quarter wave radials? If elevated, Quarter wave drooped radials? * * * Philosophical ponderings follow * * * * The discussion of radials usually attends ground mounted studies in the 100M band in the 1930s. Those studies sought to reduce loss while mimicking a conductive ground of infinite extent. Radiators taller than Quarter wave were treated to feedpoint loading (such as found in the current topic, albeit with the possibility of it being elevated and thus muddying the philosophy here). All such historical (and current AM band engineering) feedpoint loading presumed, basically, a non-resonant ground system. As Quarter wave long radials imply resonance (at least in the first read), this would suggest that, perhaps, this "tuning" should be further examined in light of feedpoint loading. The conclusion, to my mind, would be that significant reduction in feedpoint loading could be accomplished by tailoring radial length (much less drooping that is already part of the lore). At first blush, it would seem that the radials would be shorter than Quarter wave (forgive me for not first confirming this astonishing leap of faith). Of course, there is every chance some reactance will remain to be "tuned" away (returning us once again to loading) - if the mismatch is deemed significant. If such is the case, and returning to the original design, what problem is the Quarter wave length radial rule of thumb responding to? * * * * Alternative analysis * * * * Or to put it into the light of other antenna topological discussions, and in this regard the off-center fed dipole. Here we have an off-center feed (we rarely go on to describe all such installations as "vertical dipoles"). We can fully expect that, as such, we are transforming the expected 70ąj0 Ohms into some other value. Quite frequently in an OCF design, it is much higher - and variable by the degree of offset. However, for a fixed frequency, this is better understood and can be anticipated. The proximity to ground and the geometry (the radials certainly disturb the shape of an OCF dipole, even if vertical) further change things, but conceptually the monopole with resonant radials still constitutes an OCF design that is "on center fed" for the vertical element when it, too, is a Quarter wave in length. For many prospective feed points along the length of the OCF dipole, the only consideration needed is for a ratio transformation, not tuning. This is usually resolved in a BalUn. Hence "loading" is removed from the picture through careful consideration of the whole antenna, the degree of offset, and not through arbitrary assignment of Quarter wave length radials to all vertical designs. * * * * Conclusion * * * * * The concept of a loading coil where its length of wire "replaces" the missing length of radiator wire is a commonplace for technologists. It serves the discussion quite well at that level. The value of this length of wire's inductance is going to vary by significant value for the many coil form variables available to the technician. Hence the exactness of this "replacement" is questionable on the face of it at the engineering level of discussion. This equivalence "replacement" is forced further into unresolved exactness if we move the same coil up into the radiator (without changing the radiator's length). The same could be said with the treatment of Quarter wave length radials, which, after all, are a special and not general solution. 73's Richard Clark, KB7QHC |
Which is better: 5/8 wave vertical or J pole?
Richard Clark wrote in
: On Sun, 14 Nov 2010 02:25:50 GMT, Owen Duffy wrote: I meant to elaborate on this a bit more. (Did I hear someone groan?) If for example, the feedpoint Z of a 0.6 wave vertical over four quarter wave radials... I'll bite (or groan as the expectation demands) - why "quarter wave" radials? A rule of thumb? It is just what I modelled, so I was declaring the context. The thread started on 2m, my discussion was in that context, and the usual application would be elevated radials, I modelled free space. I used a quarter of the free space wave length. It is not that important because as you note, matching the feedpoint impedance deals with the length issue. The reason I didn't specifiy any slope is that they were horizontal. Other configurations are possible, but the numbers will vary. I suggest that as the vertical length approaches a half wave, a set of shorter radials, and perhaps three might well provide adequate decoupling... but Z will differ again. I was not trying to publish a working design, rather to give some info on the way these things behave. Owen .... |
Which is better: 5/8 wave vertical or J pole?
On Nov 13, 9:11*pm, "Peter" wrote:
Why do you call it a 1/8 wave loading coil? It wouldn't be along the lines of the flawed "loading coil replaces the missing degrees" concept would it? I referred to the 1/8 wave loading coil without really thinking about it. I was unsure of the loading coil dimensions, so I simple tried a 1/8 wave length wire formed into a coil. This is for the simple series arrangement 5/8 radiator. This created a load coil that appeared to have a little too much L so I have removed one turn, seems to load up ok after a little trimming of the radiator. Keen to hear how too determine the value/dimensions for the loading coil. Having said that I'm not sure what so wrong with missing degrees" concept.. A 5/8 monopole's performance is quite senstive to the ground plane implementation. The behavior of a 5/8 monopole over a perfect ground is not replicated over real radial systems or car roofs, yet people compare antennas based on the perfect ground plane environment. As the length of the radiator is increased beyone a half wave, low angle gain increaeses until about 0.6 wavelengths when power is shifted into a developing upper lobe. The optimum length over a perfect ground is probably just a little less than 5/8, and less still over practical ground planes. The other dimension is feedpoint impedance. For a simple series L matching arrangement, R is a little high and the optimum length is typically longer than 5/8. So, for optimum pattern, and low VSWR, a better solution is a tapped base coil with 0.6 wavelength vertical... but that doesn't play well with the simplest of mobile antenna bases that provide only one connection to the screw on antenna. My current 5/8 wave ground plan project is simply to get something on air, however I plans to construct an improved version with the tapped coil approach. I may be looking in the wrong places, but I have been surprised at how little information there is on the net regarding 5/8 wave ground plan. Thanks Owen for the above over view of the 5/8 wave ground plan. Cheers Peter VK6YSF http://members.optushome.com.au/vk6ysf/vk6ysf/main.htm- Hide quoted text - - Show quoted text - The way you did it works pretty good. A lot of practical antenna work is estimate and trim.There is or used to be a site that goes into a lot of detail on the 5/8ths. I had it in my bookmarks for a long time but lost it in my last computer crash. Compares 5/8ths with 1/4 wave radial 5/8 radials horizontal and drooping radials and much more. Sorry but I cant remember who had the site bet someone here does. Jimmie |
Which is better: 5/8 wave vertical or J pole?
On Nov 13, 10:21*pm, JIMMIE wrote:
On Nov 13, 9:11*pm, "Peter" wrote: Why do you call it a 1/8 wave loading coil? It wouldn't be along the lines of the flawed "loading coil replaces the missing degrees" concept would it? I referred to the 1/8 wave loading coil without really thinking about it. I was unsure of the loading coil dimensions, so I simple tried a 1/8 wave length wire formed into a coil. This is for the simple series arrangement 5/8 radiator. This created a load coil that appeared to have a little too much L so I have removed one turn, seems to load up ok after a little trimming of the radiator. Keen to hear how too determine the value/dimensions for the loading coil. Having said that I'm not sure what so wrong with missing degrees" concept. A 5/8 monopole's performance is quite senstive to the ground plane implementation. The behavior of a 5/8 monopole over a perfect ground is not replicated over real radial systems or car roofs, yet people compare antennas based on the perfect ground plane environment. As the length of the radiator is increased beyone a half wave, low angle gain increaeses until about 0.6 wavelengths when power is shifted into a developing upper lobe. The optimum length over a perfect ground is probably just a little less than 5/8, and less still over practical ground planes. The other dimension is feedpoint impedance. For a simple series L matching arrangement, R is a little high and the optimum length is typically longer than 5/8. So, for optimum pattern, and low VSWR, a better solution is a tapped base coil with 0.6 wavelength vertical... but that doesn't play well with the simplest of mobile antenna bases that provide only one connection to the screw on antenna. My current 5/8 wave ground plan project is simply to get something on air, however I plans to construct an improved version with the tapped coil approach. I may be looking in the wrong places, but I have been surprised at how little information there is on the net regarding 5/8 wave ground plan. Thanks Owen for the above over view of the 5/8 wave ground plan. Cheers Peter VK6YSF http://members.optushome.com.au/vk6y.../main.htm-Hide quoted text - - Show quoted text - The way you did it works pretty good. A lot of practical antenna work is estimate and trim.There is or used to be a site that goes into a lot of detail on the 5/8ths. I had it in my bookmarks for a long time but lost it in my last computer crash. Compares 5/8ths with 1/4 wave radial 5/8 radials *horizontal and drooping radials and much more. Sorry but I cant remember who had the site bet someone here does. Jimmie I modeled a few of the usual versions. http://home.comcast.net/~nm5k/acompari.htm I had thought I had also modeled a few using resonant 3/4 wave radials, but I guess I had found better modeled results using the 5/8 radials. But I know the 3/4 wave radials give a much better pattern than the 1/4 wave radials, but maybe a tad less gain than 5/8 radials. But these show why I don't like 1/4 wave radials for a 5/8 radiator. And Richard may have a point about it it being an "OCF" antenna. This is why I consider it perverted. I don't like horizontal OCF antennas either.. :( Through the years of modeling these, and playing with them in the real world, I've noticed a few things about the radials. I prefer sloping 1/4 wave radials when used with a 1/4 wave radiator. The performance difference between "straight out" radials is not large, but is about .3 db or so better with the sloping variety. And you get a bit better match. But sloping 1/4 radials with a 5/8 radiator is bad news. The pattern is even worse than when they are straight out. So if one were to use 1/4 radials on a 5/8 GP, they should be straight out for the best results. But I much prefer using either 3/4 or 5/8 radials with a 5/8 radiator, and the plots show why. The pattern is cleaned up, and the high angle lobe does a vanishing act. You then start to see the comparative textbook gains at the horizon when comparing to shorter antennas. IE: most books will claim a 5/8 antenna to have appx 3 db gain vs the 1/4 wave. But you won't see that with the short radial version. The gain is there, but it's not on the horizon where you want it. If you look at the azimuth plot for each, note the 1/4 GP shows about 1.8 dbi, and the 1/2 about 2.1 dbi. As they should.. But look at the perverted 5/8 version.. A lowly 1.1 dbi at the horizon, with most of the real gain shooting off to venus at about 45 degrees.. The antenna is sad, and needs therapy.. :( Where is the appx 3 dbi we are supposed to be seeing? But if you check the version with sloping 5/8 radials, we see our expected gain on the horizon. About 3.1 dbi in this plot. That's pretty close to the theoretical expectations. But if you make the long radials even steeper to more closely resemble the collinear, the gain increases to 4.25 dbi. You are starting to approach the gain territory of the dual 5/8 collinear which will show about 5.1 dbi on the horizon. Assuming good decoupling from the feed line of course... Decoupling is half the battle, and if it is ignored, one might as well hang a wet noodle on the roof, and be done with it. This explains why I have such a negative view of 1/4 wave radials under a 5/8 whip. It's like using a band aid to deal with severe chainsaw lacerations. The blood with still spew, and it will be spewing up into the air at about 45 degrees from the horizon. Chortle.. All the speculation about matching seems silly to me. The matching coil is so simple to apply, it's a non issue. I've built so many of them, I can tell you about how many turns to use for any particular band.. I can usually just guess, and get pretty close. Maybe tweak a turn or two to get just right.. It's simple, and any matching schemes should not interfere with the lengths of the elements if you want the most gain at low angles. It's like matching a yagi.. I don't alter the element lengths of a yagi to get a batter match. I use the appropriate matching scheme, and leave the elements the length they were designed to be for the gain/fb the antenna was designed to produce. |
Which is better: 5/8 wave vertical or J pole?
|
Which is better: 5/8 wave vertical or J pole?
On Nov 13, 8:25*pm, Owen Duffy wrote:
If for example, the feedpoint Z of a 0.6 wave vertical over four quarter wave radials was 150-j500, your tapped coil matching network can be designed using bulk standard circuit theory to transform 150-j500 to 50 +j0, and nowhere do you use the missing 54° in those calcs. That's because the lumped-circuit model assumes that all signals travel instantly at faster than light speeds through the coil. At instant, faster than light speeds, the coil cannot possibly occupy any degrees of the antenna. When the real-world speed of light limit is taken into account by using the distributed network model, the degrees occupied by the coil falls out as part of those real-world calculations. The lumped-circuit model is simply flawed for the purpose of trying to determine the degrees occupied by the coil. I am finishing up an article on this subject. At 3.5 MHz, the velocity factor of the 100 turn, 10 inch long coil is 0.04, which makes the coil occupy 26.4 degrees when used for a 3.5 MHz mobile antenna. The "Axial Propagation Factor" from the Hamwaves Inductance Calculator at: http://hamwaves.com/antennas/inductance.html can be used to determine the number of degrees occupied by a loading coil. For the above coil at 3.5 MHz, the axial propagation factor is 1.8118 radians/meter. Multiplying by 1.4554 converts it to degrees/ inch. The coil is 10 inches long so: 1.8118(1.4554)(10) = 26.4 degrees occupied by that loading coil at 3.5 MHz. We can model a transmission line as lossless, but none exists in reality. We can model a loading coil that occupies zero degrees of the antenna, but none exists in reality. -- 73, Cecil, w5dxp.com |
Which is better: 5/8 wave vertical or J pole?
On Nov 14, 9:36*am, wrote:
On Nov 13, 10:21*pm, JIMMIE wrote: On Nov 13, 9:11*pm, "Peter" wrote: Why do you call it a 1/8 wave loading coil? It wouldn't be along the lines of the flawed "loading coil replaces the missing degrees" concept would it? I referred to the 1/8 wave loading coil without really thinking about it. I was unsure of the loading coil dimensions, so I simple tried a 1/8 wave length wire formed into a coil. This is for the simple series arrangement 5/8 radiator. This created a load coil that appeared to have a little too much L so I have removed one turn, seems to load up ok after a little trimming of the radiator. Keen to hear how too determine the value/dimensions for the loading coil. Having said that I'm not sure what so wrong with missing degrees" concept. A 5/8 monopole's performance is quite senstive to the ground plane implementation. The behavior of a 5/8 monopole over a perfect ground is not replicated over real radial systems or car roofs, yet people compare antennas based on the perfect ground plane environment. As the length of the radiator is increased beyone a half wave, low angle gain increaeses until about 0.6 wavelengths when power is shifted into a developing upper lobe. The optimum length over a perfect ground is probably just a little less than 5/8, and less still over practical ground planes. The other dimension is feedpoint impedance. For a simple series L matching arrangement, R is a little high and the optimum length is typically longer than 5/8. So, for optimum pattern, and low VSWR, a better solution is a tapped base coil with 0.6 wavelength vertical... but that doesn't play well with the simplest of mobile antenna bases that provide only one connection to the screw on antenna. My current 5/8 wave ground plan project is simply to get something on air, however I plans to construct an improved version with the tapped coil approach. I may be looking in the wrong places, but I have been surprised at how little information there is on the net regarding 5/8 wave ground plan.. Thanks Owen for the above over view of the 5/8 wave ground plan. Cheers Peter VK6YSF http://members.optushome.com.au/vk6y...htm-Hidequoted text - - Show quoted text - The way you did it works pretty good. A lot of practical antenna work is estimate and trim.There is or used to be a site that goes into a lot of detail on the 5/8ths. I had it in my bookmarks for a long time but lost it in my last computer crash. Compares 5/8ths with 1/4 wave radial 5/8 radials *horizontal and drooping radials and much more. Sorry but I cant remember who had the site bet someone here does. Jimmie I modeled a few of the usual versions.http://home.comcast.net/~nm5k/acompari.htm I had thought I had also modeled a few using resonant 3/4 wave radials, but I guess I had found better modeled results using the 5/8 radials. *But I know the 3/4 wave radials give a much better pattern than the 1/4 wave radials, but maybe a tad less gain than 5/8 radials. But these show why I don't like 1/4 wave radials for a 5/8 radiator. And Richard may have a point about it it being an "OCF" antenna. This is why I consider it perverted. I don't like horizontal OCF antennas either.. *:( Through the years of modeling these, and playing with them in the real world, I've noticed a few things about the radials. I prefer sloping 1/4 wave radials when used with a 1/4 wave radiator. The performance difference between "straight out" radials is not large, but is about .3 db or so better with the sloping variety. And you get a bit better match. But sloping 1/4 radials with a 5/8 radiator is bad news. The pattern is even worse than when they are straight out. So if one were to use 1/4 radials on a 5/8 GP, they should be straight out for the best results. But I much prefer using either 3/4 or 5/8 radials with a 5/8 radiator, and the plots show why. The pattern is cleaned up, and the high angle lobe does a vanishing act. *You then start to see the comparative textbook gains at the horizon when comparing to shorter antennas. IE: most books will claim a 5/8 antenna to have appx 3 db gain vs the 1/4 wave. But you won't see that with the short radial version. The gain is there, but it's not on the horizon where you want it. If you look at the azimuth plot for each, note the 1/4 GP shows about 1.8 dbi, and the 1/2 about 2.1 dbi. As they should.. But look at the perverted 5/8 version.. A lowly 1.1 dbi at the horizon, with most of the real gain shooting off to venus at about 45 degrees.. The antenna is sad, and needs therapy.. *:( *Where is the appx 3 dbi we are supposed to be seeing? But if you check the version with sloping 5/8 radials, we see our expected gain on the horizon. About 3.1 dbi in this plot. That's pretty close to the theoretical expectations. But if you make the long radials even steeper to more closely resemble the collinear, the gain increases to 4.25 dbi. You are starting to approach the gain territory of the dual 5/8 collinear which will show about 5.1 dbi on the horizon. Assuming good decoupling from the feed line of course... Decoupling is half the battle, and if it is ignored, one might as well hang a wet noodle on the roof, and be done with it. This explains why I have such a negative view of 1/4 wave radials under a 5/8 whip. It's like using a band aid to deal with severe chainsaw lacerations. The blood with still spew, and it will be spewing up into the air at about 45 degrees from the horizon. Chortle.. All the speculation about matching seems silly to me. The matching coil is so simple to apply, it's a non issue. I've built so many of them, I can tell you about how many turns to use for any particular band.. I can usually just guess, and get pretty close. Maybe tweak a turn or two to get just right.. It's simple, and any matching schemes should not interfere with the lengths of the elements if you want the most gain at low angles. It's like matching a yagi.. I don't alter the element lengths of a yagi to get a batter match. I use the appropriate matching scheme, and leave the elements the length they were designed to be for the gain/fb the antenna was designed to produce.- Hide quoted text - - Show quoted text - Thanks thats the data I was looking for but I dont believe it is the same site. More than good enough. |
Which is better: 5/8 wave vertical or J pole?
On Sun, 14 Nov 2010 10:08:24 -0500, John Ferrell
wrote: While there is no "best solution" to most antenna configurations, understanding the decisions you make and utilizing the available resources make a big difference in the outcome. Hi John, True, this has everything to do with utility. I hope you guys can keep the thread going for a while, you are answering questions that I have been unable to ask! It's easier to keep the thread going (productively) if you could choke up a question. If I were to rummage for key points in the hopes of doing what you ask, I could as easily bore you (everyone). Fishing for just such an example, and returning to both drooping radials on a 5/8ths and how that might cause this design to suffer equally with the worst of J-Pole performances, let's look at the silhouette of the 5/8ths with drooping radials: Overall, it gives us a radiator that starts out 5/8ths tall (radials out at 90 deg), or gets "taller" as those radials droop. In the extreme (radials fallen to 0 deg), we now have a 7/8ths tall radiator (my aforementioned OCF vertical dipole). Neglecting problems of feedpoint Z, this radiator lobe pattern could be pushed beyond the two towards developing four lobes. Without checking this in EZNEC (left for the student to perform), this could result in transforming an already higher gain antenna into becoming a cloud warmer. This (the additional, higher lobes) is often the fate of the J-Pole when the line that feeds it becomes part of the radiator. We get glowing reports of how well J-Poles have been built and matched, and sometimes grief over how deaf they are (How could this be?). 73's Richard Clark, KB7QHC |
Which is better: 5/8 wave vertical or J pole?
"JIMMIE" wrote in message ... On Nov 14, 9:36 am, wrote: On Nov 13, 10:21 pm, JIMMIE wrote: Thanks thats the data I was looking for but I dont believe it is the same site. More than good enough. That is interesting. Just when I thought I was getting a handle on things its back to the old drawing board! Keen to hear comments on the plots presented per the link. http://home.comcast.net/~nm5k/acompari.htm -- Peter VK6YSF http://members.optushome.com.au/vk6ysf/vk6ysf/main.htm |
Which is better: 5/8 wave vertical or J pole?
"Ralph Mowery" wrote in message m... "David" nospam@nospam wrote in message ... I would not say any of the simple veticals are better. While I have not tried them from fixed locations, expirimenting with several differant mobile antennas over the years it seems that one type is not really that much beter than another. Depending on the direction and height of the repeaters almost any antenna can be better going into one repeater and worse going to another. Several of us got together and put several antennas (one at a time) on the same mount of a car. Depending on the particular repeater, there was not one overall winner. The car also had a 40 meter loaded whip that we tried and it was actually better into some of the repeaters. About the only antenna overall not suited was a colinear about 6 feet long. It worked well enough while parked, but at highway speeds it whipped around so much the mobile flutter made it almost unusable. My experience with mobile vertical whips has been similar, I guess at least in my case the location of the antenna was always a compromise and car body's are not designed to be ideal ground plans. I did get quite good at knowing where some of the good lobes were and positioning the car accordingly. -- Peter VK6YSF http://members.optushome.com.au/vk6ysf/vk6ysf/main.htm |
Which is better: 5/8 wave vertical or J pole?
On Nov 14, 9:32*am, Cecil Moore wrote:
On Nov 13, 9:35*pm, Richard Clark wrote: This equivalence "replacement" is forced further into unresolved exactness if we move the same coil up into the radiator (without changing the radiator's length). From a conceptual standpoint, there is no "unresolved exactness". Considering a base-loaded antenna vs a center-loaded antenna: I am writing an article that conceptually explains it all. The first part of the article has been published: http://www.eham.net/articles/24940 -- 73, Cecil, w5dxp.com |
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