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Yagi efficiency
When one looks at a.radiating array pattern one can see that the yagi
is very inefficient. Does anybody know of the relative volume contained in the main radiation lobe versus the total volume of the entire pattern? I know there are a lot of different type antenna gains and arrangement but I am trying to determine in an informal way the efficiency ratio and compare it to what would appear to be a very efficient antenna such as a dish. A casual look at a yagi radiation pattern would suggest that it is less than 50% efficient at best especially when considering DX work where even the main lobe is less than 50% efficient when looking at available signal paths beyond 4000 miles which are somewhat below 12 degrees and where the main lobe itself is centered between 13 and 14 degrees with an average amateur antennah Art |
Yagi efficiency
art wrote:
When one looks at a.radiating array pattern one can see that the yagi is very inefficient. Please define "efficiency". -- 73, Cecil, http://www.w5dxp.com |
Yagi efficiency
On 21 Sep 2006 17:05:44 -0700, "art" wrote:
When one looks at a.radiating array pattern one can see that the yagi is very inefficient. Art, this suggests that you have an unconventional view of the meaning of the term "efficiency", perhaps you should elaborate. Owen -- |
Yagi efficiency
art wrote:
When one looks at a.radiating array pattern one can see that the yagi is very inefficient. Does anybody know of the relative volume Art Art Yagis, when made of almost anything but something like nichrome wire, are very efficient. Aluminum element yagis run in the high 90's of percent efficiency when properly designed. My bet is that you aren't speaking of efficiency at all, but something you don't know the words to express. Try to explain what you mean, and this group may be able to help you. tom K0TAR |
Yagi efficiency
Well this is where I am comming from, I am presently building an
antenna for this winter where I will be communicating with the U.K. Thus my major lobe needs to be robust between about 10 degtrees and 4 degrees to ensnare most of the communication. Notwithstanding that the upper half of the major lobe serves no usefull purpose to what the antenna is required for there is a mass of radiation in many directions and levels that have no connection to the required purpose of the antenna, thus we have a lot of wasted radiation that if we harness it so that it is used for the antennas primary use the efficiency of the antenna would increase immensly. So to the question, accepting that the major lobe is required in its entirety for the antennas required use I feel that less than 50% of available radiation is used for the antennas design usage and that also includes the upper lobe as not being a positive contributor However I have no real figures to hang my hat on........ O.K.? Art Tom Ring wrote: art wrote: When one looks at a.radiating array pattern one can see that the yagi is very inefficient. Does anybody know of the relative volume Art Art Yagis, when made of almost anything but something like nichrome wire, are very efficient. Aluminum element yagis run in the high 90's of percent efficiency when properly designed. My bet is that you aren't speaking of efficiency at all, but something you don't know the words to express. Try to explain what you mean, and this group may be able to help you. tom K0TAR |
Yagi efficiency
Tom Ring wrote: art wrote: When one looks at a.radiating array pattern one can see that the yagi is very inefficient. Does anybody know of the relative volume Art Art Yagis, when made of almost anything but something like nichrome wire, are very efficient. Aluminum element yagis run in the high 90's of percent efficiency when properly designed. Hmmmmm I would question your logic on that figure. since I am not aware of the normal ratio between actual resistance versus radiation resistance which would point to the manufacture of radiation energy relative to the total energy input however my question relates to the efficient radiation to the requirement at hand Art tom K0TAR |
Yagi efficiency
On 21 Sep 2006 19:09:38 -0700, "art" wrote:
Notwithstanding that the upper half of the major lobe serves no usefull purpose to what the antenna is required for there is a mass of radiation in many directions and levels that have no connection to the required purpose of the antenna, thus we have a lot of wasted radiation that if we harness it so that it is used for the antennas primary use the efficiency of the antenna would increase immensly. Hi Art, The classic solution is to stack yagis vertically. This draws down the higher radiation lobes and puts their gain in the forward direction. However, unless you can positively insure that higher radiation does not actually find its way to the target (you need a propagation modeler to prove that, by the way), then you could be muffling yourself at one elevation to yell at another elevation that is only heard in points remote from the target. In other words, if you suppress the lobe at 20 degrees to optimize the lobe at 10 degrees, you may miss your target altogether. Given that skip works on so many variables, an "efficient" antenna may be wholly useless. 73's Richard Clark, KB7QHC |
Yagi efficiency
Richard Clark wrote: On 21 Sep 2006 19:09:38 -0700, "art" wrote: Notwithstanding that the upper half of the major lobe serves no usefull purpose to what the antenna is required for there is a mass of radiation in many directions and levels that have no connection to the required purpose of the antenna, thus we have a lot of wasted radiation that if we harness it so that it is used for the antennas primary use the efficiency of the antenna would increase immensly. Hi Art, The classic solution is to stack yagis vertically. This draws down the higher radiation lobes and puts their gain in the forward direction. Well you are getting closer to the question at hand. You have now doubled the power input but only slightly gained directionality(2db) efficiency I would also suspect that you have flattened the lower lobe only into a pancake shape. But again I go back to the desirable radiation which can be said in this case to be the lower half of the major lobes half power envelope which for a directional radiated array is very small compared to the total radiated field.True propagation can play games but the ARRL give the average arrival angles over a 11 year period so it is not a hopeless task to get a ball park figure regarding usefull radiation knowing where the target is I suppose I could make a model and slice out the half power lobe portion and compare the two volumes for myself, I just thought that it had already been looked at Oh well back to the drawing board Art However, unless you can positively insure that higher radiation does not actually find its way to the target (you need a propagation modeler to prove that, by the way), then you could be muffling yourself at one elevation to yell at another elevation that is only heard in points remote from the target. In other words, if you suppress the lobe at 20 degrees to optimize the lobe at 10 degrees, you may miss your target altogether. Given that skip works on so many variables, an "efficient" antenna may be wholly useless. 73's Richard Clark, KB7QHC |
Yagi efficiency
On 21 Sep 2006 19:19:52 -0700, "art" wrote:
Tom Ring wrote: art wrote: When one looks at a.radiating array pattern one can see that the yagi is very inefficient. Does anybody know of the relative volume Art Art Yagis, when made of almost anything but something like nichrome wire, are very efficient. Aluminum element yagis run in the high 90's of percent efficiency when properly designed. Hmmmmm I would question your logic on that figure. since I am not aware of the normal ratio between actual resistance versus radiation resistance which would point to the manufacture of radiation energy relative to the total energy input however my question relates to the efficient radiation to the requirement at hand Art Art, from Wikipedia and me, some definition that might help you express your problem in conventional terms: Directivity is a property of the radiation pattern produced by an antenna. It is defined as the ratio of the power radiated in a given direction to the average of the power radiated in all directions. Gain is the product of the efficiency of the antenna and the directivity. Efficiency is the ratio of total power radiated to power into the antenna. Efficiency of practical Yagis is very high as Tom has told you. Loaded / trapped Yagis are not so efficient due partly to losses in the loading coils / traps. This is the same issue that commonly arises with shortened antennas. It is quite wrong to say in general "that the yagi is very inefficient". You seem to be talking HF, the azimuth beamwidth of most practical HF Yagis is so large that you are unlikely to notice much difference in gain within 3 deg of boresight, so on a fixed heading you would expect to cover the 10 deg to 4 deg target area comfortably with little variation in gain. If you want to maximise the transmitted signal for that specific path, you should minimise losses (eg avoid lossy traps and coils, feed system losses etc), increase directivity (more elements, better design), pay attention to the desired path elevation (eg mounting height of the antenna). Owen -- |
Yagi efficiency
On 21 Sep 2006 20:16:31 -0700, "art" wrote:
give the average arrival angles over a 11 year period so it is not a hopeless task to get a ball park figure regarding usefull radiation knowing where the target is Hi Art, It is instructive for others to consider, so I shall proceed with very few of those variables considered (we can see you offer nothing in the way of time of year, time of day, frequency, Sun spot count, and so on): 20M 0000 UT Spring 5-7 deg 20M 0000 UT Summer 4 deg 20M 0000 UT Fall 6-8 deg 20M 0000 UT Winter 7 deg 20M 1200 UT Spring 3 deg 20M 1200 UT Summer 2-10 deg (depending) 20M 1200 UT Fall 2-3 deg 20M 1200 UT Winter 4-6 deg 40M 0000 UT Spring 10 deg 40M 0000 UT Summer 8-12 deg 40M 0000 UT Fall 3-12 deg (depending) 40M 0000 UT Winter 3 deg The numbers above say absolutely nothing about the probability of making a contact. If you stacked 4 to 8 yagis as high as 4 wavelengths, you might find something "efficient." 73's Richard Clark, KB7QHC |
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