Loosing on 900Mhz AP

Alright I’ll give some backstory just so everything is understood.

I manage networks for the Wisp I work for. And we have this one city that has been giving me problems fairly consistently. Pretty much ever since we put it up.

It’s been at least 4 years now since we’ve been there and we have both 2.4 Gear (Cisco) and 900Mhz Gear (Canopy, was Trango)

There have been some competitors that moved in the area quite a while back and that’s fine. (By fine i mean we had to retrofit all our 900mhz customers with canopy gear because they were tx’ing on the freq we were using and having GPS sync’d canopy gear was the only solution for me to keep my customers) This was a few years ago. But all of the sudden recently i’ve been getting massive error rates on any of my customers links below -55dBm Trying to find a solution i’ve talked to the city (they operate 2 900mhz scada units) and to the other Wisp. We started by shutting my equipment down and doing a spectrum sweep with just the scada systems offline. the noise in my freq band is at about a -65 or so. So i had the other wisp shut down his gear at the same time as our system and the scada. Then did a spectrum sweep. But i couldn’t find any other transmissions on our frequencies. (noise floor at about -70 [TX from distant towers]). So basically i’m thinking something has gone wrong with my equipment.

So i’ve replaced my radio, lightning arrestor, SyncPipe/Sync Injector. Checked all my coax and even replaced it, but still i have these issues.

I’ve even tried putting a CMM up with GPS just in case the syncpipe failed. And still i have gotten no where.

I was running 8.2.7 firmware and my competitor was running 9.3 so I updated to that.
We’re both using the same settings 75%dl/ul 10miles and 3 control slots.
I’ve tried changing frequencies, and that helped slightly (for about 30 minutes but then LQ began to degrade) but it was killing all my competitors customers on that channel. because it is the one that is aimed towards my tower.

I do run an omni, because most of my customers are on 2.4ghz and due to all the afore mentioned interference issues i had lost some of those customers in the past. So it doesn’t make fiscal sense to deploy a sector setup.

One other thing of note, there is a CDMA cellular carrier on my tower as well.

My competition has been pretty keen to work with me here in that city, whereas in the past they weren’t but i’m not about to look a gift horse in the mouth.

Basically i’ve just run out of idea’s, if anyone else has any i’m definitely open to them.

It most definitely sounds like interference. Is there anything in the area that would be frequency hopping? That will stomp all over you in a heartbeat.

Do a spectrum analysis from your Canopy AP with everything else online. You’ll probably be seeing noise into the -50s which is why those customers can’t stay connected. Watch the spectrum and see if you can find a null to work with.

I have one site where I had a problem like this and the only spot I could broadcast was right around 912MHz.

There are definitely things that are 900mhz frequency hopping.

My competition has a 900mhz alvarion FHSS unit. But that’s been there for years But i see that at about a -60,65 .

Also the City has two FHSS Scada’s on 900Mhz. But i’ve already had them shut down while i tested. and i didn’t see any difference in my error rates. Plus they’ve been there for a couple of years as well.

I honestly figured it was some sort of RF interference but with a spectrum analyzer running (anyritsu not built in canopy) I still can’t seem to find any. I even left it on max hold for a few minutes, hoping to find the spikes of some Hopping gear.

As for changing frequencies, there’s really not any more open frequencies to move to. as my noise floor from my competition on 915-8mhz and 906Mhz-8Mhz the 915 is at about -45 and the 906 is about a -55. I’ve tried moving to 915 and i got much better uplinks but horrible downlinks to my customers. Plus i took most of the customers on his 915AP offline.

what about 924?

Some cell carriers run in the upper 890’s-902or so. that would definitely cause problems for you on 906.

924 is where i am currently located.

The cell carrier. runs about 880 if my last conversation with them was correct.
I know i also run the risk of running into paging services (930- ) But i don’t see the appropriate spike just off the charts in this location


another option, maybe try putting a bandpass filter inbetween your radio and your omni. we have had to do this once or twice in our network.

That’s not a half bad idea. I had considered it before. But didn’t think it would do me much good because i wasn’t seeing much spill over of frequency. and the other high power sources of RF are all on syncronized canopy radios

Do you know of anywhere i can get a 900Mhz bandpass filter for an 8mhz wide channel?

http://www.lastmilegear.com/category.ph ... t2=Filters

Thanks Much. I really hope this works. I’ve got a few bandpass filters installed on my trango gear. But i’ve never used one for canopy before.

In the meantime if anyone else has any ideas as well. I’m sure open.


wifiguy wrote:

Those are the ones we use.

I have had so much interference on 900 that I am in the process of dismantling my 900 wisp and moving everyone to other bands. My experience is that we do well with 2.4 even through some trees. We have 900, 2.4, and 5GHz. at all of our AP sites anyway (all Canopy, btw). We just started with 900 and left those customers on 900 that were there originally. Anywhere I can’t reach a customer on another band, I am negotiating a site lease close to them so that I can last hop to them with 802.11 if needed.

Since my competitor wisps continue to operate their canopy equipment with non-gps sync and seem to want to follow my APs to the next frequency in which I move, I just can’t get much coverage. Generally has to be -45 or better to make things work correctly.

And, since my competitiors are being such jerks about all of this, I am building a very high powered 3 channel 900Mhz. Amateur TV repeater station at my central NOC just so that the local Hams can have ATV access when they want.

I can understand and definitely identify with the 900mhz having too much interference. But there are too many trees around here for any other frequency band for a lot of rural people.

I did have one more question for everyone.
I’ve got my order in for the Bandpass filter. and at 1-2db of loss pluss the loss of the lightning arrestor. I’m not near my PtMP limit of 36dBm 26dBm-2dBm-1dBm+9dBm=32dBm EIRP
But adding a 1W amp inline before all the other devices would give me this

But i’m worried about an amp throwing the sync timing off. As i know they aren’t instantaneous devices. Also does the Bandpass filter add any appreciable delay to the system?

I know the canopy has a offset for delay product. But i’m not sure if it will be large enough to need to compensate for. As i’ve never had an amp on a canopy before. Especially when they were 28dbm which coupled with the 9dBm antenna would put me pretty close to the max EIRP every time.

Thanks again everyone

Just an update in case anyone reads this.

I was completely unable to find, and resolve the interference. I replaced everything of mine on that tower.
I installed a bandpass filter in case it was out of band interference.
Basically i’ve lost this tower on 900.
Makes me very upset because I’ve spent so much time and money converting people because of interference.
But in the end it’s the price we pay for unlicensed bandwidth.
I’ve already negotiated a secondary location near that tower. but outside of town that we will be deploying 900 on so maybe i can shift the customers outside of town to that location.

I’m glad that some of my customers that i couldn’t service can get service from outside of town from the competing ISP so they’re not completely out of service. But I guess at a certain point you just have to wonder if the other isp’s are truthful with you, or would just like to take your customers and they’re really the root of all your problems. Or if it’s just all coincidence and it’s just something you missed.

Oh well time to put my Tech license to good use other than 2meters and put up a 900mhz atv station. Always wanted to be on tv :slight_smile:
50W ought to do it.

I digress i’m not that malicious.

I appreciate everyones input with this.


That’s a shame. I’ve never lost a broadcast site but I’ve lost large chunks of the band available to me. There are several of my locations where I’m on my last usable section of the band - anything changes there and I’m in trouble.

You said it though, we chose unlicensed so this is the web we weave.

I’m going to jump in here.

You said that your spectrum (with everything off) was about -65 and customers with worse than -55 were dropping off. This is exactly how it should be. I assume you are running 2X enabled. 2X requires the customer and AP to each receive a signal that is 10db stronger than the noise floor from their perspective. If either is less than 10db greater then there will be a problem…

Yes that would normally be the case, but i’ve even set the ap to use 1x only mode which should operate down to a 3dB SN ratio. If my memory serves correctly.
The normal -65 i see on my channel is from a competing wisp using the same timing(slots ul/dl control) settings as well as a CMM. So really when i’m rx/tx i shouldn’t be seeing that noise level either.
I’ve already gone about deploying a secondary tower closer to town to be able to service what i have left of a customer base. Needless to say it’ hasn’t been pretty.
But i do appreciate all the help everyone has given me.