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How not to mount an Omni

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kg9dw's picture
How not to mount an Omni

I'm one of those learn from my mistakes, and learn more from others' mistakes kind of guy. So in the interest of furthering the community, I present KG9DW's Mesh Mistake #103: Mounting an OMNI the wrong way.

Here's how I mounted an M5 rocket with a 13db omni:

Notice that the antenna runs parallel to the top of the railing for about 6". This was done in a hurry, the same day we pulled two 100+ft runs of cable up the elevator from the remote eletrical room along with mounting the new PTZ camera. Everything seemed to work great...I had 3 nodes connecting in, one at .5 miles, one at 5 miles, and one at 1.5 miles. But I was seeing a lot of drop packets - on the OMNI node, LQs were down in the 40s, but NLQs were always 100%.

So up to the top of the elevator I went last Friday. I picked a very sunny day, but it was windy (>20 mph at the top) and the elevator was running grain (very dusty and noisy). First I plugged in a power brick right at the antenna and hooked up the laptop. Yep, LQs were still in the 40s. I tried moving frequencies, but that didn't help. There are two WISPs at this site, with 8 dishes, 3 OMNIs, and 4 sector antennas.

I decided to try to get the antenna away from the rail a bit. First I laid it on the concrete roof:

Well that's funny. The LQs went to 100 with the OMNI laying on the roof. Time to make a permanent change. (BTW, notice the semi in the background...that's corn for corn chips, high fructose corn syrup, frosted flakes, and animal feed.)

While some hams would have whipped out the zip ties and electrical tape to secure it horizontally on top of the concrete roof, I decided to resort to a short piece of pipe and two clamps. 

Ahhhh....much better. LQs all up at 100 and NLQs the same. Throughput is much better now as well. I should have noticed that before, but I was just excited to get it to work! In the last picture you can see the OMNI on the new pole, then to the lower right is the PTZ camera that is connected to it. (The nanobridge in the picture is for one of the WISPs, and the antenna is a GPS augmentation signal in the 450MHz band for John Deere equipment used by the local farmers.)

So lessons learned:
1. Don't side mount OMNIs to anything such that the antenna is obstructed. 
2. Don't work on antennas on the top of the grain elevator on windy days, even if it is 70 and sunny.

Mesh on my friends. 

I suppose its not surprising

I suppose its not surprising after the fact to think that obstruction would have such an impact, but I could see how it might slip through when actually mounting.

Appreciate the feedback of just how much an impact that area had and good to know these dual polarity omni's really do need to be clear.

KD2EVR's picture
I'm just happy to learn that

I'm just happy to learn that there is a MIMO omni avialable.  I had been trying to steer folks towards Nanostations due to the dual-chain capability. 

kg9dw's picture
Rockets rule

For a hub type deployment, the Rockets are hard to beat. And things are looking up on the XW hardware front (team looking for testers, beta software out!) which means finding a Rocket XM won't be a requirement. I've got two omnis setup and they work OK. 5 miles seems to be the limit and that's because one side of the link is a nanobridge at 25+DB and the other side is an omni at 13DB. Once you get used to seeing SNR up in the 30s because you're running two 25DB dishes pointed at each other, it takes a bit to get used to having an omni on one side!

If you have any questions about hardware recommendations, feel free to start a thread on the forum. There a pluses and minuses to each device on the supported hardware matrix.

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