Antenna Instal

[wconn]

General question..Recently our VFD had a repeater system and antenna installed. Our antenna is approx 100 ft in the air on the tower which sets around 1380 elev. The antenna installer was not able to get the antenna in the center due to a rotatable ladder that moves 360 deg on the top of the tank. Our antenna is off to one side of the tower, but still above ithe tower.The antenna is a Sinclair omni with 6 deg downtilt. Has anyone had a water tower causing issues with their antenna. It seems that our coverage favors the side that has the antenna mounted on it. We do not have much of a signal approx 2 miles from the site at our FD. Almost like anything in the direction of the towe is blocked off. Any recomendations or thoughts?.

 

[mmckenna]

Sounds like the tank is creating a shadow.

The antenna would need to be mounted on top of the tank, preferably in the center, to fix that.

Question would be if that can be done. Without seeing it, hard to say.
Not casting shade on your specific installer, but -some- installers get lazy and will slap the antenna up where ever it is easiest. You might want to have someone take a look at the tower and engineer a way to put the antenna dead center.

Depending on the type of tower, you might be able to put the antenna lower, but that would reduce overall range, but fix the shadow.

Or, just find another location.

 

[wconn]

There is a walkway around the tower with railing. I was thinking if we went with another taller antenna such as the DB 420 mounted on the side facing our district area may work.our current antenna is around 9 or 10 feet.

 

[jfr]

.......creating a shadow.

.......casting shade on your specific installer

I see what you did there!!!

-JR

 

[mmckenna]

There is a walkway around the tower with railing. I was thinking if we went with another taller antenna such as the DB 420 mounted on the side facing our district area may work.our current antenna is around 9 or 10 feet.

If the water tower is in the center of the desired coverage area, then you want the antenna on top of the tower. If you can't go on top, you need to find a way to get the antenna well above the top of the tower.

If the water tower is on the edge of your coverage area, then mounting the antenna on the side of the tower facing the desired coverage area would help.

If the tower is more or less in the middle, and getting the antenna up higher is not an option, a power divider could be used and two antennas used. Two antennas on opposite sides of the water tank.

Really, to me, sounds like your installer got lazy, or didn't look at the install before quoting you the price. Someone with some experience should have known better.

Based off this, I have someone else come and take a look at it, and get a better solution in place. And while they are at it, double check all the other work the installer did, since it's now sort of suspect. If they cut corners on the antenna install, no telling where else the cut corners.

 

[mmckenna]

I was thinking if we went with another taller antenna such as the DB 420 mounted on the side facing our district area may work.our current antenna is around 9 or 10 feet.

Adding to what I wrote above.

I think it would be a waste of money to start guessing at this point. A taller antenna might get it up a bit higher, but there's still going to be shadowing.

The higher gain antenna will increase your system ERP and that may cause it to violate what your license allows.
In other words, getting a professional involved would likely save you a lot of money, especially if you want this to work well.

There are ways that the antenna mounting can be modeled using software. A good radio shop should be able to figure this out.



On a different tangent, I should say it -seems- like it's the tank causing a shadow. Could be other things, too. But on the surface, it sure seems like the mounting location is the issue.

Lemme guess: Low bid?

 

[prcguy]

Is the 1,380 elevation above sea level or average terrain? Or the real question should simply be, how high is the antenna above average terrain?

I think 6deg downtilt is a bit on the aggressive side even for 1,380ft above average terrain and if the antenna is barely sticking above the water tank the downward radiation pattern will put some of the tank in the way. You might be at a point where raising the antenna just 10ft might make a noticeable improvement. How far do you need to communicate from this repeater in all directions?

 

[Golay]

Antenna

wconn, take a picture of it and post it.

 

[lmrtek]

Your down tilt antenna is likely being blocked by the tank.
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The only way to get good water tank omni coverage is to be high enough above the tank to have a clear line of sight to where you want to cover.
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Most of your pattern on the tank side is likely being blocked due to downtilt.
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As someone who has multiple antennas on multiple water tanks, i can say that the best choice is always to use a smaller antenna mounted higher in the air than a larger one mounted lower.
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Using a Sinclair unity gain antenna which is far smaller and lighter will allow it to be mounted much higher thus providing better coverage.
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They also provide a much wider vertical pattern which will fill dead spots far better than any downtilt design.