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Discussion Starter · #1 ·
The documentation is very vague. I'm not sure which settings need to be changed in the YGO3.cfg file. Supposedly it outputs the element spacing and length, but there is a place for this to be entered in the .cfg file? It takes almost a hour to run so it's a waste of time if you don't know exactly what your doing. Is there a site that explains this program a little better?


Thanks,

Glenn
 

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Glenn


This looks like a useful program.


Most optimizing programs need you to enter min and max values of each of the "free parameters" as well as a starting guess for the "free parameters". In this case, the free parameters are the dimensions of the director elements, the active element, the reflecting element, and the spacing between elements.


The program requires the values in the ygo3.cfg file to be filled in by the user. I would leave most of the data alone except for the areas which concern you.


For example, a 3 element Yagi in the example requires you to specify the "seed" file, here named ygo3seed.dat from which the starting values of the free parameters are taken, the version of the NEC analysis file name which is most appropriate for the number of elements in your Yagi, and min, max values of the element dimensions. The max, min values in the sample cfg file allow for up to 50 elements, and I don't believe you should change any of the values in the lenghty gene table at the end of the ygo3.cfg file


The above comments are from only a cursory examination of the data. I'll study in more detail over the next day or two and I'll give you more explicit instructions.


I recommend that you start with a small number of elements and slowly graduate up to a large number of elements.
 

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Discussion Starter · #3 ·
cymro,


Thanks for offering to help. This is a very interesting program, I'm not sure if I'm designing a antenna or a new life form http://www.avsforum.com/ubb/smile.gif


What ohm should I be using? Everything I've read so far uses 50ohm, but they are usually radio antennas, not TV. Or should it be 75 or 300? Will this require a special balun?


I'm not sure how the FOM is set. Seems like only 2 options?


Perhaps only the element radius should be set in the Gene Table. I want to use a constant diameter, but have the option to swap out different lengths.


I want to build a longer version of the JBX21 with more elements, but only if the results make sense. Otherwise I will just build a precision, no compromise version of the JBX21 with adjustable element spacing for fine tuning certain bands or channels.


Glenn
 

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Hey Glenn,


Well, you've gone and done it now. It has been a number of years since I used the program. As far as impedance goes, it is going to depend on how you feed or match to it. Most TV antennas use a 300ohm to 75 ohm balun to convert from the balanced 300 ohm impedance of the "dipole" driven element to the 75 ohm unbalanced impedance of the coax. That is probably the best way to go. If I remember correctly, there were a bunch of canned antenna designs in there that might be easy to modify. Amateur antennas designed for 432 MHz or 70cm should be able to be shortened up to meet your needs.


..Doyle
 

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Discussion Starter · #5 ·
Hi Doyle,


Hope this isn't opening a new can of worms for you. Should I be changing the default 50 ohm to 300 and use a standard balun? It seems like the radio guys go through great lengths to tune the feed line, I hope I won't need to do that with a multiband TV antenna.


The freeware version that I have does not have any examples, do you have the full version. Maybe you could email me one of the examples unless there is somewhere that I can download it.


Thanks,

Glenn
 

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Would someone post a link where the freeware version can be downloaded?
 

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Status Report on using Yagi Optimizer,


I have now used the Yagi optimizer to design a 50 ohm, 23 element antenna for a 144MHz frequency. (this is the frequency used in the example provided by the author of the program).


The resulting antenna had about 16 dbi gain (ref isotropic antenna) which isn't too bad. Its impedance was quite low - about 20 ohms - compared to the target of 50 ohms. The f/b ratio and f/r ratio were about 20db. The beam width was around 25 degrees.


The optimization took around 18 hours to run on my 2666MHz Pentium II laptop.


Now I am starting the design of a 23 element antenna for 300 ohm impedance optimized over the US UHF band, ch 14 to ch 69 (470 MHz to 806 MHz). This optimizing run will probably take 60 hours. I will compare the design with a Blake DY20WB antenna which has 20 elements, but also uses a corner reflector that cannot be used in the Yagi optimizer software.


When I have done a few more runs, I will post explanations on how to use this software. Since the runs take such a long time, it might be a week or more before I post again in this thread.



DUH: Although I know something about genetic optimization, I know only enough about antennas to be dangerous. I have just learned:


UHF antennas use bow ties for the driven element so that the bandwidth of the antenna is broadened. The impedance of a bow tie likes to be around 300 ohms; the impedance of a dipole, OTOH, likes to be around 50 to 75 ohms.


So, this particular Yagi optimizer is only good for narrow bandwidth, e.g. a single UHF channel, and we should not ask the optimizer software to achieve an impedance of 300 ohms.


With the above in mind, I'm going to "get a life" and forget about the Yagi optimizer; however, if anybody wants to know how to run the program, please let me know.




[This message has been edited by cymro (edited 05-17-2001).]
 

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Discussion Starter · #9 ·
cymro,


Thanks for your efforts in looking at this program. It looks like it may not work for these types of antenna? I'll give you a call to discuss it in more detail.


Glenn
 
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