I am considering a dual band 2m/70cm antenna something like the Comet GP-9 (17ft antenna). I have several mounting options and I am trying to decide which one is best.
I have a 30ft tilt down tower (Universal Towers 12-30) with a 10ft, aluminum 1 1/2 inch diameter 1/4 in wall mast on top of that for a total height of 40ft. At the top of the 30' tower I have a large TV antenna (I kept it low due to wind loading). At the top of the 10ft mast I have a Cellular (850MHz) Yagi. I know that the best place to mount something like the GP-9 would be above the Yagi, but I am not sure I have enough room to bring the tower down (or actually even get it up) with the Comet extending for a total of 57ft. Or actually I should say I am pretty sure I don't have room. I have trees that are about 60ft from the tower and I am pretty sure I don't have 57ft of clearance to the branches to raise/lower the tower. From what I remember the 40ft just cleared, but I might have another 5-10ft of clearance.
So, assuming I don't have clearance to mount the antenna at the top, I was looking at side mounting it further down the 10ft mast based on how much clearance to the trees I end up having for raising/lowering it. I looked into that and see that when side mounting to a tower you want, I believe it was, a 1/2 wavelength separation between the tower and the antenna. For the 2m band that is 39in which is quite a bit. I don't think I can do that.
My question is if mounting it along the side of a 1 1/2in mast, is just as bad as mounting it close to a full tower side? I suspect that mounting it right along a mast will be bad for tuning/VSWR, but I am not positive. I don't care if the only impact would be a null in that direction. But I would care if there were side nulls 30deg from there or so.
A second option would be mounting a much shorter (maybe 5-6ft) dual band at the top of the tower just above the 850Mhz Yagi (I think I have the clearance for that). That would put the base of the antenna at 40ft and the tip at ~ 45ft.
A third option would be to mount the larger GP-9 on top of a ~25ft 1 1/4 steel mast that I have in a cement base next to the house and a bracket at the peak of the roof that attaches the mast to the house. That would put the base of GP-9 a few feet above the peak of the roof and the tip a total of about 42ft high. The complicating issue there is that I have a metal roof (nothing is ever easy).... Now the base of the antenna would be above that, but not by much.
So it breaks down to:
1) Put the larger, higher gain antenna at the highest point, but some or most of it will run close and parallel to an aluminum mast.
2) Put a shorter, lower gain antenna on top at 40ft.
3) Put the larger antenna on top of a lower mast, but the total height to the tip is about the same as the shorter antenna on the tower, but the base is only a few feet above a metal roof.
Any ideas on will #1 work at all? If not would #2 or #3 be better?
Thanks
I have a 30ft tilt down tower (Universal Towers 12-30) with a 10ft, aluminum 1 1/2 inch diameter 1/4 in wall mast on top of that for a total height of 40ft. At the top of the 30' tower I have a large TV antenna (I kept it low due to wind loading). At the top of the 10ft mast I have a Cellular (850MHz) Yagi. I know that the best place to mount something like the GP-9 would be above the Yagi, but I am not sure I have enough room to bring the tower down (or actually even get it up) with the Comet extending for a total of 57ft. Or actually I should say I am pretty sure I don't have room. I have trees that are about 60ft from the tower and I am pretty sure I don't have 57ft of clearance to the branches to raise/lower the tower. From what I remember the 40ft just cleared, but I might have another 5-10ft of clearance.
So, assuming I don't have clearance to mount the antenna at the top, I was looking at side mounting it further down the 10ft mast based on how much clearance to the trees I end up having for raising/lowering it. I looked into that and see that when side mounting to a tower you want, I believe it was, a 1/2 wavelength separation between the tower and the antenna. For the 2m band that is 39in which is quite a bit. I don't think I can do that.
My question is if mounting it along the side of a 1 1/2in mast, is just as bad as mounting it close to a full tower side? I suspect that mounting it right along a mast will be bad for tuning/VSWR, but I am not positive. I don't care if the only impact would be a null in that direction. But I would care if there were side nulls 30deg from there or so.
A second option would be mounting a much shorter (maybe 5-6ft) dual band at the top of the tower just above the 850Mhz Yagi (I think I have the clearance for that). That would put the base of the antenna at 40ft and the tip at ~ 45ft.
A third option would be to mount the larger GP-9 on top of a ~25ft 1 1/4 steel mast that I have in a cement base next to the house and a bracket at the peak of the roof that attaches the mast to the house. That would put the base of GP-9 a few feet above the peak of the roof and the tip a total of about 42ft high. The complicating issue there is that I have a metal roof (nothing is ever easy).... Now the base of the antenna would be above that, but not by much.
So it breaks down to:
1) Put the larger, higher gain antenna at the highest point, but some or most of it will run close and parallel to an aluminum mast.
2) Put a shorter, lower gain antenna on top at 40ft.
3) Put the larger antenna on top of a lower mast, but the total height to the tip is about the same as the shorter antenna on the tower, but the base is only a few feet above a metal roof.
Any ideas on will #1 work at all? If not would #2 or #3 be better?
Thanks
