900Mhz Registration issues

We are deploying 900Mhz units and have observed some strange behavior with the SMs. In two instances while testing to determine the best placement for the unit on a site, the SM has simply stopped registering and appears not to be able to get a signal at all. In both cases we were getting a signal that was fair but not great and suddenly the unit begins to report a status of scanning and will not register. We immediately powered up a spare unit and were able to register easily and both installations were successful. In the third case we were conducting test surveys with a unit near a new tower location when the SM just went dumb. In this case we powered the unit down and did a reboot and when it powered up we were back in operation. Has anyone else seen this kind of behavior.

Yes I’m having the same experience… A new SM plugged in will register immediately and then begin to fail to register and alternate between scanning syncing , registering after a few minutes. During that time i can see the ap on the alignment screen with jitters of 4-7 rssi 1000-1200 but it won’t register, or if it does only for a few minutes. I tried two different sm’s today on top of a 180ft tower 16 miles from the ap. The other one I had was 15 miles on a water tower and session log showed 4300 re registers in 3 days. This only seems to happen in marginal signal areas, although I have seen the same thing at 2 miles through trees. Very Frustrating Can somebody help?

Sounds like some of the same stuff I have seen except I was getting RSSI in the high 1300 and low 1400 and Jitter of 3 to 4 when the things just went stone deaf.

the more I use 900, the more I see that it takes -80db and preferably higher than that to make a useable path. That is usually 1400-1500 rssi.
vert or horiz pol doesn’t seem to make any difference for us

I absolutely agree it is beginning to look like anything under 1450 will cause trouble.

define…trouble…[aside from ray lamontagne’s new album…] :slight_smile: we’ve seen RSSI and dbms around 1100…some even 1000 and haven’t had a lick of trouble yet. now we HAVE seen at least one situation where although we had the same RSSI and JITTER as another customer less than a mile away, the link was not NEAR as solid. we also saw a condition over the weekend…a 12 mile shot LOS from one ridge to another…RSSI and JITTER 1200 / 3 , should have worked great…couldn’t communicate at all with a ping or link test.

of course, our “no problem” zones are once we establish a good link, register, and keep that registration for longer than 5 minutes. :slight_smile:

what kind of trouble are you guys seein?


Ok Guys for what it is worth We have been working the 900 stuff for about two months. We have a decent number of customers on line to give us a good sampling.

We have had re-reg problems from the get go. We have some customers under 2 miles from the tower so deep in the trees that you can’t see the house and one customer that is over 10 miles away (cant see the tower from there either). We even got some so close to the tower you could run CAT 5 to em.

Through a costly trial and error process we have learned that perfect alignment is critical. Close aint good enough.

On Channel intereference from the power company, Pipeline companies, and Oil field companies and other SCADA sources is a REAL problem. Lots of folks use the 902 to 928 band to run FHSS Scada systems. These things will kill you and they are near impossible to find. Unless you run the Spectrum analyzer for a long time you may miss them. Just because you can’t see them with the SM analyzer don’t mean they aint there. Some of them come up and fire for a few seconds every few hours. they knock you down and then are gone. Bang you got a Re-reg.

The Maxrad antenna has not been kind to us. We have gone to Yagis to narrow the beam width and limit the interference. this seems to be working in some cases. In at lease two cases we are obviously shooting directly into the interference and this didn’t help. The only case were we have successfully used the Maxrad is LOS within two miles of the tower.

Short Answer the 900 stuff will drill through the trees like crazy with two to three miles unless there is OCI. The combination is deadly.

Deploying the 900 is not for faint of heart.

We have done a lot of SCADA work in our area with 900 Mhz stuff. We just got our 900 demo kit the other day and I am nervous about it. I did some bench tests and found with no interference at least -80 dBm is needed to keep errors down. The SM would still sync up at -90 and a bit lower (wow) but the BER was huge. 4e-4 Only until -80 would the BER drop to zero. Again, that’s on the bench with no interference (back to back with attentnuation). I will find out what it’s like in the “real world” in a week or two.