[TowerTalk] worlds biggest yagi

[Pete Smith]

Another notion that occurs to me is that with the Steppirs, you could 
detune some of the antennas at any given time.  That *might* produce a 
situation where you could run, say, an 8-high close-spaced stack (optimized 
for 10 meters), and then "remove" some of the antennas from the stack for 
15 and 20.  You'd still have $3-400 K left for land.

The idea of individually tuning the antennas (on each band) to compensate 
for their distance from ground (or from each other) is intriguing.  I have 
always wondered how you could put identical yagis in an HF stack and not be 
giving away something in gain or pattern.

73, Pete N4ZR

At 09:59 AM 3/28/2008, Jim Lux wrote:
>Its from Onion wrote:
> >
> >
> > 
> http://www.1982crew.com/PHP-Nuke/PDF/K9LTN.pdf<http://www.1982crew.com/PHP-Nuke/PDF/K9LTN.pdf> 
>
> >
> >
> > the sad thing:
> > No modeling was done to adjust phase distortion differences
>
>"phase distortion"?
>I assume you mean the time delay differences and the general phase
>shift?  Not some sort of narrow band dynamic effect.
>
> > between the top arrays and the bottom arrays.
>   I addition the splitter circuits were not phase coherent
>
>If you assume that you can adjust the actual radiated phase by changing
>element lengths (which is the case with a SteppIR), then you might be
>better off spending your time on the control algorithm than on
>obssessing about a wideband power divider driving interacting loads.
>This isn't like a 440 EME array where the antennas don't interact as
>much and doing power dividers with simple equal length transmission
>lines of the appropriate impedances.
>
>Conceptually, it would be like taking two antennas fed in parallel, and
>tuning one a bit high (so it has a R+jX feedpoint Z) and one a bit low
>(so it has a R-jX feedpoint Z), which would shift the relative phases,
>because of the reactive component.  There's some circulating current
>between the antennas through the combiner, but it can be pretty small,
>so the absolute loss is small.
>
>
> > and the side by side optimal spacing would not track to other bands.
>
>Any design with fixed positions of the elements, either along the boom,
>vertically stacked or horizontally displaced, is a compromise to a
>certain extent.  So you build what's practical.
>
>
> > He would have saved a lot of money just stacking two antennas at 190 
> and 160 feet.
>
>He would have saved even more money putting up a G5RV, to take it to an
>extreme.
>
>  > He spent $500,000 chasing the last 3-4 dB.
>
>He spent $500K having fun, which is what it's all about.  Some people
>spend $100K on a cruise around the world. Some people spend $100K on a
>Tesla roadster. Some people spend $100K on a ticket for a future ride
>into space.
>
>The cool thing about amateur radio is that everybody gets to try their
>own ideas (it's not like there's a mob of angry shareholders and a board
>of directors asking you whether you've gotten the best return on
>investment here).  Were I doing the same project, I might have gone to
>an all driven element approach and not bothered with the elevation axis.
>However, that's just me.  Others might have spent a much smaller sum on
>two antennas in a stack, and spent the rest of the money on buying land
>for that stack in a different location.
>
>
>Jim, W6RMK
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