Hey Captain .
Like I said at the start of this I have a bunch of them around might as well use them up .
Murray
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Stacking three A99`s
- Thread starter murdog
- Start date
Like I said at the start of this I have a bunch of them around might as well use them up .
Murray
I think you will find that vertical stacking is ridiculous due to heights and supporting structure and horizontal stacking requires very accurate determination of distances and cutting of phasing lines all in order to gain an extra couple dB at the most. If you find that stacked A99's give you more gain than that then you will have encountered that psychological gain figure I mentioned. Go for it and have fun and learn something while doing it but don't expect any miracles about huge gain differences. IMHO unless you want to learn about phasing then it is far more trouble than it's worth and this is coming to you from someone that has played with antennas for 38 years and actually installed and maintained commercial phased vertical arrays on the broadcast band. AM broadcast sites will leave you with a wealth of learning experience but they will also leave you with a bruised forehead from beating it against the wall while trying to tune everything into shape.
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.
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.
If you just want to tinker I would do some research on the old Super Scanner and see if it provides any ideas.
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Hm, how would I do it. First of all' I think the time effort and expense far out ways the benefits . On a single mast the phase lines will be in the rf fields of the lower ants distorting the pattern..
I have seen it done at uhf with off set folded dipoles and the lines fed inside the mast offsets.On 27mhz this isn't practical.
HM........70ft wooden mast with a A99 up top..........
What I was thinking was making a co linear design instead, using the A99s as parts.,. maybe bottom A99 then a 1/2 phase section then another 1/2wave radiator then another phase section, then make top radiator from a gutted A99. or maybe make a coax co linear pulled up the mast and using an A99 as the top section.
Have to give it a bit more thought !
I have seen it done at uhf with off set folded dipoles and the lines fed inside the mast offsets.On 27mhz this isn't practical.
HM........70ft wooden mast with a A99 up top..........
What I was thinking was making a co linear design instead, using the A99s as parts.,. maybe bottom A99 then a 1/2 phase section then another 1/2wave radiator then another phase section, then make top radiator from a gutted A99. or maybe make a coax co linear pulled up the mast and using an A99 as the top section.
Have to give it a bit more thought !
Plans have changed 80 foot pole now no expense have miles of everything for the job and will be going ahead with it .
Yup looking for a control box , just in case !!!
This might work good if you can figure out how to wire the control box.
