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[TowerTalk] Stacking question

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Subject: [TowerTalk] Stacking question
From: (Ian White, G3SEK)
Date: Thu, 11 Nov 1999 22:29:53 +0000
Tom Osborne wrote:
>Hi Gang
>I've been wondering about some things.  Say 2 3 element
>monobanders are stacked, the gain goes up 3 db (at least that's
>what I think).  If there is 100 watts going to the antennas, when
>it reaches the splitter does 50 watts go to each antenna or does
>the full 100 watts reach each antenna.  If only 50 watts, it
>doesn't seem like there is actually any gain in stacking antennas
>as the gain goes up but the ERP is the same as with one antenna. 

No, the ERP is doubled:
 same total power radiated * twice the gain (3dB) = twice the ERP.

What happens is that the voltages received from each antenna add in
phase (in the optimum direction) which actually gives an increase of 
(2*voltage) = (4*power) = 6dB. But you divided the available power
between the two antennas, so you lose 3dB, giving a net stacking gain of

73 from Ian G3SEK          Editor, 'The VHF/UHF DX Book'
                          'In Practice' columnist for RadCom (RSGB)

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