multipath, NLOS what?

So i did a 900 install today. We have an MTI omni on a water tower about 80 feet in the air. I installed a customer 1.5 blocks away, basically LOS.

It was odd though. I installed on the back of his garage (metal sided) about 8 feet off the ground. Its about 4 feet back from the edge of the garage pointed parralell to the garage, their is a 12 inch overhang 2 feet above.

I could see the AP antenna, the radio initially connected, then dropped out and an AP eval showed nothing. 1 foot down it linked up fine. At this point though I was locked into the mount because I had alreasy fastened into the wall. I tried another radio with the same results.

Finaly I put a two foot extended DS arm on and it worked just fine.

with out 2.4 alvarion this woulda been a no brainer and worked from the get go. Is multipath or something ofthe sort differrent with the 900 gear? this was really odd that a nlos radio wouldnt stay connected when it was basically in a LOS environment.

Even if I was blinding the AP (I had turned power down to 15) you would think the AP eval would have shown something, especially since it had already linked once. Is it possible the AP is blinding the SM? if so, do I need to wrap this bad boy in tin foil or something?

Sounds to me like reflection. We try to mount things as close to the edge nearest our AP as possible due to situations like these - especially with tin.

I can’t count the number of times we made this mistake in the early days, having to either extend the mast several feet or move it elsewhere to fix the signal problems.

with the 2.4 this isnt an issue, Im new to 900, I expected to see similar results, but with 900 its this much more pronounced?

I’ve had issues at 2.4 as well, but I know from my experience it was a lot more noticeable of an effect at 900MHz.

Yes, I have a install I did starting out - about 20FT up mounted on the edge of a metal roof, at the peak. The entire metal roof is behind the SM. Its only about 7-8 miles. Using a 14db M2. It is not consistant at all. Drops randomly. This is not LOS, but mostly open farm land, with a few tree lines in between.

SM is V10, with 9.0 software.

I have considered putting trying a grid instead or the M2 17 - but it is way big…

EVERY time I have installed on a metal building with 900 I have had problems.

Elevating to at least 6’ above the roof and getting to the very edge of the building sometimes works.

A grid will probably help as it has better f/b rejection.

The metal building was causing your problems. We see this a lot in our area as a lot of people have tin roof tops, or tin siding. The problem is more pronounced at 900MHz than it is at 2.4 or higher.

Getting spacing between the antenna and building is critical. Also, run your site survey from multiple points on the roof top as not all locations will test the same.

Welcome to the world of 900MHz.