[TowerTalk] 6m Yagi 10' from a 10-15-20 Tribander

[jimlux]

On 5/20/19 10:33 AM, Michael Clarson wrote:
> Modeling is a great tool for predicting antenna performance, but it is only
> one tool in our arsenal, not the only tool..  In the article link I sent
> out earlier, it was not "someone's guess", but information based on actual
> measurements. When modeling, there is always the chance of an incorrect
> assumption or leaving out one of the variables etc. In this case, I would
> take Kent's measurements and see if the modeling program predicts the same
> results. If not, adjusting the model would be in order. Once the model is
> adjusted to predict the same results as the actual, real world
> measurements, then one can scale the frequencies and materials sizes and
> see what the model predicts using Richard's antennas. -- 73, Mike, WV2ZOW


The OP was looking at 6m Yagi relative to a tribander (10,15,20, 
presumably?) spaced at 3m (10 ft) (1/2 wavelength at 6m, 1/3,1/5, 1/6 
wavelength at higher frequencies).
He didn't mention whether his tribander is a interleaved (FORCE 12, 
type) or loading coil variety.  If the latter, one of the segments 
between the boom and loading coil, or the tips, could be the "wrong" length

However, the two antennas used in that article (for 440 and 915 MHz) 
aren't particularly representative of 3 element beams on related bands.
For example, the two bands (70cm and 33cm)  don't have any low order 
harmonic relationships. They also have a lot of elements (particularly 
the 33cm antenna)

Since none of the elements in one antenna is close to a multiple of a 
resonant size in the other antenna, the interaction will be limited.

Also, at the closest spacing (5.5" - 14cm) the antenna spacing is 0.2 
wavelength (for 70cm) and 0.42 wavelength (for 33cm)


I don't know that this data dispels any rules -


> 
> On Mon, May 20, 2019 at 1:07 PM <john at kk9a.com> wrote:
> 
>> Good advice, it is always best to model it to see the true interaction
>> instead of relying on someone's guess.
>>
>> John KK9A
>>
>>
>> Jim jimw7ry wrote:
>> Yes.
>>
>> I had to turn my 4 element 90 degrees from my tribander to keep it from
>> effecting it. According to the modeling program that K5GO used.
>>
>> Although mine is about 4 feet above the tribander.
>>
>> Best to model it.
>>
>>
>>
>> Thanks
>> 73
>> Jim W7RY
>>
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