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Author Topic: Antenna separation/interaction question  (Read 1033 times)
NZ0T
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Posts: 74




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« on: August 12, 2011, 07:14:33 PM »

I am putting ny tower back up after a move and i have a question about separation of antennas.  The plan is to put up, from the top, a Comet GP-3 vertical, a home brew 12/17 meter rotatable dipole and a Cushcraft A3 triband 3 element yagi.  I have about 10 feet of mast to work with above the tower.  I am thinking of putting the dipole about 3 feet below the vertical and then the A3 right at the bottom of the mast which would be about 7 feet below the dipole.  Is this enough separation to stop any interaction between the antennas?   

73 Bill NZ0T
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AB5Q
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Posts: 202




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« Reply #1 on: August 16, 2011, 07:31:59 PM »

At 7' the dipole is right at the edge of the effective aperture of the A3 assuming a forward gain of 5.86 dbd on 20m. More is better however 7' would be a minimum separation distance in my opinion.  Interactions between the GP3 and the dipole will be minimal even at 1' of separation, the antennas are on two completely separate planes. Offset the G3 clamp perpendicular to the dipole.  To further enhance field separation between the two HF antennas, I would suggest rotating the dipole 90 degrees so that the dipole is parallel to the A3 boom. This would also allow you to bring the two HF antennas into closure proximity if necessary to reduce tower loading.

Be sure to calculate the bending moment on the mast/tower that your final scenario will create. Base your calculations on the sum of all antenna and mast loads. This result may significantly reduce the maximum allowable stacking distance in order to remain within the design limits of the tower.

73,
John - AB5Q
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