| Author |
Message |
    
Danusee
Member
Username: Danusee
Post Number: 60
Registered: 10-2004
| | Posted on Monday, January 22, 2007 - 8:04 am: | 
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I have read in a real world test that you can pick up 4 db gain away from the tower if you have a dipole mounted on the side of it. Also you get 14 db rejection. What if you put a water pipe say 5% higher than the antenna will be straight up from the rotor. At the center have a T coming off it and mount a dipole. Then you could rotate the entire "whatever you would call it" like a beam. Would this work?
Second, if the above worked, what if you came off the rotor with a water pipe again 5% higher but this time come off the bottom from a T and mount a A99 spaced again like you would a yagi w/ or w/o a gpk. Wonder what would happen and what kind of gain would you get? If if worked it would be a easy project. Also you could support the top of the A99 with pvc to keep it in align. Let me know what you think.
Dan |
Bruce
Senior Member
Username: Bruce
Post Number: 4326
Registered: 9-2003
| | Posted on Monday, January 22, 2007 - 10:25 am: |
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YES YOU CAN a good book is the ARRL antenna handbook |
Tech833
Moderator
Username: Tech833
Post Number: 1594
Registered: 8-2002
| | Posted on Monday, January 22, 2007 - 10:12 am: |
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Best you can hope for with side mounting is about 3 dB. That is, IF you mount the antenna exactly 1/4 wave away from the tower (or pole) and keep it from swaying. Closer or further spacing does do some neat stuff with the pattern. For instance, if you mount the antenna 1/2 wave from the tower, you get a bi-directional pattern perpendicular to the axis between the tower and antenna. A full wave away and you get a four leaf clover pattern. |
Marconi
Advanced Member
Username: Marconi
Post Number: 682
Registered: 11-2001
| | Posted on Monday, January 22, 2007 - 10:36 am: |
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I, for one, am not seeing what you have in your mind, but I think you are missing the principal of the side mounted dipole. First off a single bay dipole will not give you the 4 db gain you note.
Sounds like you have a mind to put the dipole in the horizontal with an A99 above it. That will work, but it won't have the gain you mention above. It will give you an advantage in horizontal polarization which could be noticable with DX or other similar polarized stations, however.
What is the source of the real world test you note above? |
Danusee
Member
Username: Danusee
Post Number: 61
Registered: 10-2004
| | Posted on Monday, January 22, 2007 - 7:35 pm: |
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I was wanting to try to mount the A99 on the side of a mast pole by using a water pipe T just above the tower. The mast will be 5% taller than the antenna. Then I would be able to turn the entire setup around with a rotor. I was hoping it would give enough gain to make it worthwhile + it would have rear rejection.
I kinda run out of things to try and that seemed like it might work. I could stabilize the top of the a99 with pvc. If it picked up 5db over dipole with rejection wouldn't be bad (just a guess).
I didn't want to run into some weird swr problem
having a99 to close to the mast. It would be just as easy coming off the center with a T to a dipole.
Wonder how it would hold up in the wind? 1/4 wave length out might be a little long for stability. Also I don't know how to figure the GPK in. I supose I could try it without then add it later. Let me know what you think.
Dan |
Marconi
Advanced Member
Username: Marconi
Post Number: 683
Registered: 11-2001
| | Posted on Tuesday, January 23, 2007 - 9:41 am: |
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Danusee, the nature of matching in the A99 uses a tuning coil device in the base. This coil device is very likely reactive to nearby conductive elements as well. If you attach the A99 to the pipe you suggest the tune may well be adversly affected. Spacing is a consideration here and may be a problem on its own.
I know that your idea is attempting to use the pipe as a reflector, but it may simply detune the antenna. This idea can be tested near the earth, so if you have the room I suggest you do that before mounting on your tower. |
Danusee
Member
Username: Danusee
Post Number: 62
Registered: 10-2004
| | Posted on Tuesday, January 23, 2007 - 6:49 pm: |
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Marconi, What you said is what I thought might be a problem. I think that I might come off the center with a dipole using the pipe as a reflector. Wonder if it would beat the A99 both at the same height @ the top? |
