[TowerTalk] Measuring resonance of a yagi element

[Jeff Blaine]

When I see this thread, it brings back memories.  Doing this accurately 
is far more difficult than one would think.  If you come away with a 
"how hard can it be" - then you are probably not considering the 
infinity of error sources.

My solution?  Cut the element and measure it in place where it would be 
used.

Impossible?  then trust the model.  If you are building a beam with 
insulated elements and no traps, assuming the model matches the build 
otherwise, it will probably be "close enough."

Good luck and have fun!

73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com


On 4/22/20 1:58 PM, David Gilbert wrote:
>
>
> I agree.  When I bought my Optibeam OB16-3 and OB2-40, Tom (DF2BO) 
> didn't send me the EZNEC files but he did send me the resulting plots 
> for gain and SWR.  The manual also specified the element lengths and 
> diameters.  I took my own measurements for the 40m coils and the 
> tribander feed system, and generated my own EZNEC files.  My EZNEC 
> plots are indistinguishable from Tom's.
>
> By the way, with the help of K9RX who lived about 30 miles line of 
> sight from me at the time (we both lived on high ground with a small 
> river valley between us) we measured the actual azimuth patterns, and 
> of course I could measure the SWR plots.  They were extremely close to 
> the models as well.
>
> Modeling unknown traps might be a bit trickier, though, I suppose.
>
> 73,
> Dave   AB7E
>
>
>
> On 4/22/2020 9:34 AM, Jim Brown wrote:
>> On 4/22/2020 7:51 AM, Robert Harmon wrote:
>>> Good luck on getting the files.   They won't give you theiir Eznec 
>>> files.
>>
>> Who is the "they" in this post? I looked all through this post and 
>> quoted stuff to find "them." If you're referring to mfrs, what makes 
>> you think they use NEC for design? There are multiple modeling programs.
>>
>> It's easy enough to produce an EZNEC file for an antenna that doesn't 
>> include inductors or capacitors -- all you need a a measuring tape 
>> and a caliper to determine element diameters. In his very useful 
>> self-published "Array of Light," N6BT includes detailed descriptions 
>> of many  Force 12 antennas he designed for the company he owned.
>>
>> 73, Jim K9YC
>>
>
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