can someone look at this pic and tell me if you think if i put a 15’ tiltek omni antenna and a 900 ap on this bracket next to a sherriff department vhf repeater if it might cause me or them problems. I am just wondering if it is too close or if thee is enough frequency difference that it would matter.
http://www.info-ed.com/tank.jpg
thanks
kenny meadows
Are you adding your antenna to the structure in the middle of the photo or the one to the left? Being underneath the existing antenna is better that being beside it.
The majority of omni-directional antennas (such as the folded dipole config in the picture) have what is known as a “cone of silence” - the vertical radiation pattern is such that there is a theoretical cone coming from the antenna up and down where the signal level is not radiated at nearly the same level as from the sides - this is why many high powered antennas are not mounted side by side on cross-face mounts on towers - usually above one another.
Also, depending on the power output of the other radio (and gain of the other antenna) you may or may not have any issues with being beside it.
Hope this helps.
Aaron
yea we would be mounting it beside it they will not let us put it on the same tower as the vhf is on. see i think i can mount it on that structure in the middle with out haveing to hoist any tower up there if its not too close.
thanks
kenny meadows
Are you going for omni-directional coverage - over the water tower? If not you could mount your antenna on the middle structure just above head height - I would stand it off over the walkway approx. 2 feet. You could go two feet to the left but having it that close to the water tank could affect the radiation pattern too much.
Aaron
yea we wanted omni if i mount it to the top of that structure and its a 15 ft antenna it should be well above the dome. but the question still remains would it interfere with the vhf system or would it interfere with my 900 stuff
thanks
kenny
If you are going to be that high you will end up right beside the VHF antenna. At that point the only thing to consider is the power output of that radio, the gain on that antenna and the usage. Again, the more separation the better.
The only other option I could suggest would be to use some filtering to pass only the 900 band.
Aaron
I speak from experiance you will need at least 10 ft vertical seperation between 900ap and vhf antenna or 20 or more horizontal. where you will notice a problem is when the 900 is transmitting you will get interfearance on the reciever of the vhf radio. Even on a sm. You will be ok with 2.4 or 5.7.
so would you suggest put a couple of 120 degree horizontal antennas mounted on the cat walk around the tank?
If that is an option for you then I would say yes. Try to put one direcly below the VHF antenna and the other on the other side of the tank - this would take advantage of the front-to-back ratio of the antennas.
Aaron
It looks like to me the tower the vhf antenna is on is about 30ft tall so I think you would be safe mounting on the catwalk, but up on that center tower would be a bad idea.
ok after i spoke with the installers of that vfh system i found out that it is only a reciever which dials back out on a tele phone line to fire up a repeater 8 miles away so he said there was no transmition on that antenna so i may still have a chance with the omni what you all think.
kenny meadows
No like i stated before the 900 causes interfearance on the vhf reciever. While the 900 is transmitting you can listen to the reciever’s speaker and hear the interfearence while this is going on the VHF reciever may not hear the transmitter that is telling it to dial the phone to turn the repeater on. My best suggestion would be talk to those same installers ask them if they could go to the site with you, take a 900 ap and turn it on close to the antenna. Have them test the reciever and tell you if it is causing a problem. Their is a chance the frequency they are on is ok. You should be able to do this without installing anything so if it doesn’t work you have not wasted alot of time. If your ok then you can do your full install.
what if i use a horizontal poloarized omni like the cyclone would it be a possible canidate and mount it on the other side of the tank?
kenny meadows
info-ed Inc.