>
>Here's more data resulting from modeling stacked yagis -- in this case
>5-el 20m monobanders rather than tribanders.
>
>Modeling Software: NEC-2
>Ground Model: Sommerfeld-Norton
>Ground Dielectric Const: 13
>Ground Conductivity: 5 mS/m
>Taper: W6QHS Method
>Segs/Halfwave: 50
>
>Antenna: Hygain 205CA, Phone Setting
>Mast Position: Center of boom
>Frequency: 14.2 MHz
>
>
>Stacking Heights: 72/105 feet
>
>Lower Ant Upper Ant
> Azimuth Azimuth Gain
>-------------------------------------------------------------------------
> 0 deg 0 deg 16.02 dBi @ 10 deg elev Both in phase
> 0 deg 0 deg 13.21 dBi @ 14 deg elev Lower only
> 0 deg 0 deg 13.45 dBi @ 9 deg elev Upper only
> None 0 deg 14.14 dBi @ 9 deg elev One 205CA @ 105 ft
> 0 deg None 13.87 dBi @ 13 deg elev One 205CA @ 72 ft
>180 deg 0 deg 10.99 dBi @ 9 deg (up) 10.66 dBi @ 13 deg (low)
>
>
>Stacking Heights: 52/105 feet
>
>Lower Ant Upper Ant
> Azimuth Azimuth Gain
>-------------------------------------------------------------------------
> 0 deg 0 deg 16.17 dBi @ 11 deg elev Both in phase
> 0 deg 0 deg 13.50 dBi @ 18 deg elev Lower only
> 0 deg 0 deg 14.07 dBi @ 9 deg elev Upper only
> None 0 deg 14.14 dBi @ 9 deg elev One 205CA @ 105 ft
> 0 deg None 13.52 dBi @ 18 deg elev One 205CA @ 52 ft
>180 deg 0 deg 12.31 dBi @ 9.5 deg (up) 11.34 dBi @ 14.5 deg (low)
>
>
>These results show that there is less interaction between the monobanders
>than between the tribanders when both antennas are pointed in the same
>direction, particularly for the larger stacking separation. However, the
>gain degradation for the monobanders is actually greater than the tribanders
>for the smaller stacking separation when the antennas are pointed in
>opposite directions:
>
>Gain Degradation
>----------------------------------------------------------------------------
> 72/105 Stack 52/105 Stack
>----------------------------------------------------------------------------
>Force 12 C3 Upper -1.92 dB -2.66 dB
>Force 12 C3 Lower -1.93 dB -2.88 dB
>HG205CA Upper -2.46 dB -1.76 dB
>HG205CA Lower -2.55 dB -2.16 dB
>
>Where gain degradation is the difference in maximum gains of the same
>antenna at the same height as a result of pointing in opposite directions.
>
>It appears that you pay a performance price when you point stacked yagis
>in opposite directions. For practical purposes this will only
>be of importance for signals that are marginally above the noise. On the
>other hand, contesters spend a lot of money eeking another one or two dB out
>of their antenna systems.
>
>
>
>73 de Bruce, WA7BNM (bhorn@netcom.com)
I'm having a bit of a hard time following some of your numbers, and I think
some of them may be questionable. For instance, if I'm reading them correctly,
when you fed 2 yagis in opposite directions you got less than a 3 db
degradation. Since a pair of yagis has 3 db less power per yagi than a single
yagi (assuming equal power distribution), I would have expected a bigger
excursion ie. it should be 3db lower right off the bat. However, all the
numbers look close within about .5 db or so. I consider giving up .5 db for
the versatility of a multi-directional stack a nice tradeoff if you only
have 1 or 2 towers.
73, Tyler kf3p@cais.com
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