"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. 13457 Visits.
enlarge 108KB, 742x1024 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]
enlarge 208KB, 1024x695 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]
enlarge 222KB, 1024x696 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]
enlarge 126KB, 1024x695 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]
enlarge 33KB, 716x1024 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.]
enlarge 164KB, 1024x695 6 Impact to K6STI's 5-El Hi-VHF Yagi below kgb's 13-El UHF Yagi: Minimal impact, even at 1-ft separation.
enlarge 231KB, 1024x695 7 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 123KB, 1024x695 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 132KB, 791x1024 9 CM4228 UHF 8-Bay on top of K6STI's 5-El Hi-VHF Yagi 4nec2 File
enlarge 32KB, 791x1024 10 kgb's 13-El UHF Yagi on top of K6STI's 5-El Hi-VHF Yagi 4nec2 File
