Tower side Mount of a 2 meter antenna

[AJAT]

I have 30 foot tower with a wind generator mounted on top. I was thinking of mounting a 2 meter antenna a little lower below the wind generator using a side mount, also maybe a discone scanner antenna below it. I am concerned that the 2 meter antenna mounted on a side Mount will be to close to the tower and raise the SWR to high. I would think It would have to be at least one wavelength away about 6.7 feet. A little to far for a side Mount. Am I correct in my thinking?

 

[ka3aaa]

side mounting of antennas is fairly common and has been for a while, seven feet is fine for two meters and you may be surprised how low the swr may be. All of the antennas where my club is located has side mounted antennas on multiple towers at different elevations for our repeaters. the only thing you may get is some degreation in signal and performance where the tower is, if you were looking back towards the tower from the antenna. one thing i would recommend is use mounting kits manufactured by the towers manufacture rather than make your own and don't forget a stand off for the top of the antenna to keep it from swaying in the wind to much.

imagine an aluminum i-beam 16 feet long with a uhf station master mounted on the end mounted 150 feet in the air on a 450 foot tower. it was a pain but we did it.

 

[jeepsandradios]

So first issue will be what does the tower support. On most of my commercial towers VHF is on a 10' standoff. On one of my SAR sites we do run a APRS antenna on a 6' standoff and it works well for what it is. I guess the other item is what antenna. A 2M diamond vs a DB224 is like apples and oranges in weight and loading of the tower.

 

[prcguy]

An antenna mounted a wavelength out from a tower will have a clover leaf pattern with four lobes and four nulls.

 

[AJAT]

I was only planning on getting a stand-off that will put the antenna about 12 inches from the tower. I have not decided on an antenna yet. I am not sure about a 7 foot stand-off. The tower is guyed and bolted to a building for the first 8 feet of so. The tower was on my property when I bought it. It looks like it is in good shape. I want to be safe and not over complicate it. I was hoping the 12 inch stand off will be “good enough” to have some fun with.

 

[R8000]

I'd be more worried about vibrations from the wind generator.
At a previous employer I worked for, we had equipment on a tower with a wind generator on it (we didn't own the tower or site). We had issues with mounts shaking loose over time and needed tightening from time to time. A small point to point dish we had would suffer performance issues and the culprit was loose mounting hardware. We also had a VHF antenna that would tilt over time

At one point there were two other renters with LMR equipment on the tower and ended up moving off for the same reason. After I left the company, the point to point link was removed due to the upkeep required.

The vibrations weren't 24/7 but would depend on changes of wind speed and the turning of the generator direction for best performance. Standing at the base of the tower, I could hear the noises the generator was making, then the occasional vibrations as the wind direction changed.
We didn't have any RF performance issues beyond the vibration problems.

I don't know the output capabilities of the generator, but it was used to supplement the site owners property nearby. So, it wasn't very big. The tower was 75 feet tall on a mountain. My company had nothing to do with the operation of the generator, we just rented tower space.

I just wanted to mention this. I guess it depends on the size, make and model of the generator used will dictate stuff like this. Something to keep in mind.

 

[AJAT]

I'd be more worried about vibrations from the wind generator.
At a previous employer I worked for, we had equipment on a tower with a wind generator on it (we didn't own the tower or site). We had issues with mounts shaking loose over time and needed tightening from time to time. A small point to point dish we had would suffer performance issues and the culprit was loose mounting hardware. We also had a VHF antenna that would tilt over time

At one point there were two other renters with LMR equipment on the tower and ended up moving off for the same reason. After I left the company, the point to point link was removed due to the upkeep required.

The vibrations weren't 24/7 but would depend on changes of wind speed and the turning of the generator direction for best performance. Standing at the base of the tower, I could hear the noises the generator was making, then the occasional vibrations as the wind direction changed.
We didn't have any RF performance issues beyond the vibration problems.

I don't know the output capabilities of the generator, but it was used to supplement the site owners property nearby. So, it wasn't very big. The tower was 75 feet tall on a mountain. My company had nothing to do with the operation of the generator, we just rented tower space.

I just wanted to mention this. I guess it depends on the size, make and model of the generator used will dictate stuff like this. Something to keep in mind.

That is a good point. I am not sure about the vibration of it, but it does make some noise when the wind picks up. That is something I will keep in mind. If a do decide to install the antenna I will do frequent checks on the hardware. I usually have the wind generator shut off unless we have a good wind at night or on a cloudy day. I have solar panels that tend to “fight” the wind generator on sunny breezy days so I leave the break on. It is on my list to re-design it so they both “talk” to each other.

 

[prcguy]

At 12" off the tower the omni will turn into a 2 element beam. With about 19" being a 1/4 wavelength, 12" will loose some efficiency over an actual 2 element beam and cause the impedance to lower quite a bit.

I was only planning on getting a stand-off that will put the antenna about 12 inches from the tower. I have not decided on an antenna yet. I am not sure about a 7 foot stand-off. The tower is guyed and bolted to a building for the first 8 feet of so. The tower was on my property when I bought it. It looks like it is in good shape. I want to be safe and not over complicate it. I was hoping the 12 inch stand off will be “good enough” to have some fun with.