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I'd extend each vertical A99 out horizontally from the center of the top of the mast so that the measurement between them is a 1/4 wave.

This will help eliminate any nulling effect, plus should provide about 3dB gain.

You'll need an impedance matching device at the end of 24' of RG-213 coming from each A99.

Three 1/4 wave lengths of 87Ω coax paralleled would do the trick, but where do you find THAT?

You'll need to fab an impedance coupler, perhaps a type of transformer wound to have a 3-->1 effect.

This would be a type of 'horizontal stacking', not vertical.

If vertical stacking, the top one would need to be mounted on top of the 72' mast, the bottom on the ground and the middle A99 36' up at it's bottom in order to correctly space them, but you're still running into quite an impedance matching/phasing challenge with regard to the feedline type and lengths.

<blockquote data-quote="Needle Bender" data-source="post: 550803" data-attributes="member: 13339">I&#039;d extend each vertical A99 out horizontally from the center of the top of the mast so that the measurement between them is a 1/4 wave.This will help eliminate any nulling effect, plus should provide about 3dB gain.You&#039;ll need an impedance matching device at the end of 24&#039; of RG-213 coming from each A99.Three 1/4 wave lengths of 87Ω coax paralleled would do the trick, but where do you find THAT? You&#039;ll need to fab an impedance coupler, perhaps a type of transformer wound to have a 3--&gt;1 effect.This would be a type of &#039;horizontal stacking&#039;, not vertical.If vertical stacking, the top one would need to be mounted on top of the 72&#039; mast, the bottom on the ground and the middle A99 36&#039; up at it&#039;s bottom in order to correctly space them, but you&#039;re still running into quite an impedance matching/phasing challenge with regard to the feedline type and lengths.</blockquote>

[QUOTE="Needle Bender, post: 550803, member: 13339"] I'd extend each vertical A99 out horizontally from the center of the top of the mast so that the measurement between them is a 1/4 wave. This will help eliminate any nulling effect, plus should provide about 3dB gain. You'll need an impedance matching device at the end of 24' of RG-213 coming from each A99. Three 1/4 wave lengths of 87Ω coax paralleled would do the trick, but where do you find THAT? You'll need to fab an impedance coupler, perhaps a type of transformer wound to have a 3-->1 effect. This would be a type of 'horizontal stacking', not vertical. If vertical stacking, the top one would need to be mounted on top of the 72' mast, the bottom on the ground and the middle A99 36' up at it's bottom in order to correctly space them, but you're still running into quite an impedance matching/phasing challenge with regard to the feedline type and lengths. [/QUOTE]

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