450i SM placement

Hello all, we are deploying our very first 450i 900Mhz product in a couple of days. I was wondering if anyone has any thoughts as to SM placement tips. Since most of our customers won't have line of sight ( mostly pine trees in the way) We were wondering what we should be looking for in terms of placeing SM's high on the roof line, or are they OK, to be on the lower roof line ( about 10 feet above ground). Not sure if this makes any difference, but it will only be one AP unit serving this area. ( no special GPS sync ) .  Any thoughts or tips would be greatly appreciated. Thanks all 

That question can not be answered. You will have to have your installer find the best spot for the sm and find that happy signal and signal to noise ratio, I shoot for -70 or below and look for a very good signal to noise then speed test the m back to the ap prior to setting any QOS on the sm radio. That could mean high or low roof lines. 

What is the noise floor on the ap reading? 

we haven't even set up the AP yet, we are planning on doing that this Thusday the 21st. 

LOL, we are a very small company. So, I am the installer :)  it seems fairly easy to find a good spot in LOS situations, but in NOLOS, I wasn't sure where to even start. I guess I will need an extremely long ethernet cable to connect to a laptop to test signals from various points around each home. 

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prepare a long cable with a tripod and 10 foot pipe throw that on the roof and test, you may not need the 10foot pipe,

going from one end to the other on the house can make a difference.

you may need more than 10foot at some spots.

also if you can use your cellphone and put a gps point at your tower so you can get azimuth so you know where to point it.

 the higher the antenna is there should be less trees and all

Thank you for the tip, it is greatly appreciated. I'll post my results sometime next week assuming I get a customer online. :)


Placement depends on many factors.

Height is often your friend when it comes to 900MHz until it’s not.

Height Pros
The FZ in 900MHz is huge. Gaining height gives the radio a chance to open that up before being blocked by something. Height may also help the FZ clear more of the tree tops.

Height Cons
Increasing height may increase your exposure to interference.

Increasing height may increase your risk of the antenna becoming a lightning rod.

Use the LINKPlanner.

Be sure to ground everything properly.

And have fun.


Trees cause more problems the closer the SM is to them, so moving to the far end of the roof from them can get you a few dB, so long as you aren't moving into heavier tree coverage.  Tilting the antenna up a bit is also a good way to reduce self-interference and get over the trees, particularly if you can visually tilt it to just above the treeline.

I will often combine signal readings and visual alignment.  If the signal is pointing into a bunch of trees, I'll try to put it in the middle of the largest visible gap.  It's a bit of a compromise between what the SM tells you and what you can see for yourself, but it makes a noticeable difference in stability when the wind starts pushing the trees around.

Once you think you have it positioned properly, do a Link Capacity with the S/N calculation test enabled.  Look at the downlink and uplink S/N values, and re-align whichever direction has the lower S/N.  If either the DL or UL S/N is weak, it will impact stability, so you're better off having both DL and UL OK than one good and one poor.  The DL can be aligned via either the Alignment Tool or the Link Status tabs, but you'll need the Link Status tab to align off the UL and you'll have to do a link capacity before the values will start updating.

Generally, the UL S/N is weaker because the antenna on the AP is less directed, and the tower is less insulated from noise by trees, but that's not an absolute by any means.

If you have trouble getting an initial session, the 14.2 Beta has added a new Aiming tab to replace the broken Alignment tab.  It can be a little buggy, and sometimes you have to choose the frequency the AP is using, but it's enough to figure out where the tower is and get that initial session.  I also tend to use Google Maps to figure out which direction the tower is from the house, and then look at the satellite map of the house to make sure I'm pointing the right way.

Lastly, link capacity is  the most important thing.  The other metrics are meaningless if you aren't getting a decent capacity.  In extreme cases, I have aligned SMs by doing 5 second link capacities over and over again until I found the sweet spot.

I've spent a lot of time aligning PMP100s, PMP320s, and PMP450s in heavily treed and extremely noisy conditions.  It shows.  :-p

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