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Vert. Stacked UHF and Hi-VHF Antennas
"Typical" Hi-VHF and UHF Vertically Stacked Antennas analyzed using 4nec2 to determine minimum "tolerable" separation.
Best vertical spacing for either combination is 6-ft or more.

For CM4228 8-Bay (with Reflector Screen) stacked on top of K6STI's 5-element Hi-VHF Yagi, impact on Gain and SWR were minimal, even at 3-inch separation.
When separation was less than 4-ft, UHF CM4228's F/R Ratio was degraded 2-3 dB, mostly at lowest frequencies.
F/R Ratio for K6STI's 5-El Hi-VHF Yagi was slightly degraded, beginning at 4-ft separation, but did not become excessive until 3-inch separation.
[Separation is measured to the bottom of CM4228's Reflector Screen.]

For kgb's 13-Element UHF Yagi stacked on top of K6STI's 5-Element Hi-VHF Yagi, the impact to Gain and SWR were minimal at even small (1-foot) separations.
However, 13-El UHF Yagi's Front/Rear (F/R) Ratio was significantly degraded when they were any closer than about 4-feet.  5-El Hi-VHF Yagi's F/R Ratio was minimally impacted.

EDIT (6Mar2010 at 5:15pm): Updated some charts with 5, 6, 8 and 100-ft separations.
Date(s): 4 Mar 2010. Album by holl_ands. 1 - 10 of 10 Total. 11080 Visits.
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Enlarge photo 1
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1
CM4228 UHF 8-Bay on top of K6STI's 5-El Hi-VHF Yagi
3D View with 2-ft Separation
[Measured from BOTTOM of CM4228 Reflector Screen]


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2
Impact to K6STI's 5-El Hi-VHF Yagi below CM4228 UHF 8-Bay:
Minor impact on Gain until reach 3-inch separation.
Front/Rear Ratio okay if 7-ft or more separation.
[Measured from BOTTOM of CM4228 Reflector Screen]


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3
Impact to CM4228 UHF 8-Bay above K6STI's 5-El Hi-VHF Yagi:
Very minor impact on Gain, even at 3-inch separation.
Front/Rear Ratio okay if 4-ft (optimum) or more separation.
[Measured from BOTTOM of CM4228 Reflector Screen]


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4
Impact to CM4228 UHF 8-Bay above K6STI's 5-El Hi-VHF Yagi:
Separation had very minor impact on SWR.
[Measured from BOTTOM of CM4228 Reflector Screen]


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5
kbb's 13-El UHF Yagi on top of K6STI's 5-El Hi-VHF Yagi
3D View with 4-ft Separation
[Separation measured from Boom to Boom.]


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Impact to K6STI's 5-El Hi-VHF Yagi below kgb's 13-El UHF Yagi:
Minimal impact, even at 1-ft separation.


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Impact to kgb's 13-El UHF Yagi
above K6STI's 5-El Hi-VHF Yagi:
Minimal impact on Gain, even at 1-ft separation.
Front/Rear Ratio okay if more than 4-ft separation.


Enlarge photo 8
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8
Impact to kgb's 13-El UHF Yagi
on top of K6STI's 5-El Hi-VHF Yagi:
Minimal impact on SWR, even at 1-ft separation.


Enlarge Microsoft Word Document 9
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DOC9
CM4228 UHF 8-Bay on top of K6STI's 5-El Hi-VHF Yagi
4nec2 File


Enlarge Microsoft Word Document 10
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DOC10
kgb's 13-El UHF Yagi on top of K6STI's 5-El Hi-VHF Yagi
4nec2 File


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