Hey rculp,
Are there any Water Towers near by? Some Water Treatment and Water Quality control companies use 900 to transfmit water level and other data from the water towers to their head office. From what I’ve heard it is only checked a few times a day. Might be sometihng to look into.
Thanks for the reply.
I did find one Water Utility that has RF in the area, I talked with them yesterday. They are on a licensed 154.xxx Mhz freq. thats transmits 24-7.
Along the same lines, we have two subs that normally see the AP at -70 to -73, jitter is 3 to 4. At 1.3 miles from the AP. AP sees one at -77, the other at -82. They are across the road from each other. Prbbly 40% foliage. Both on Yagis. They both drop at the same time. I noticed that one has the “Session Timeout” perpetually at 0. The other seems to manage to renew the timeout before it reaches zero (most of the time). There are 6 other subs on this sector with no problems…
Any thoughts?
I have mentioned this in another post but it seems fitting here:
Watch for ANY cordless phones as we have seen a number of 2.4 and 5.8 phones that signal at 900MHz.
Can anyone say that a 400-800% jump in jitter even with a continued RSSI of 1800 and -62 db would be the result of interference?
SM has been up for 6 mos without re-regs. Normal jitter is 1-2 w/ 1800-2000 RSSI and -58 to -62 db’s.
Recently, the SM’s in question are getting knocked off with a jitter of 4-15.
140 re-regs overnight.
These SM’s are about 1/2 mile from AP with LOS.
At this moment the AP shows the SM’s as still registered, however I can’t access the web page or ping the SM.
Tech rolled out with a second radio rig and saw the same thing.
When you can get in the SM on occasion, a link test shows 100% uplink efficiency and a 20-30% downlink efficiency.
Is this a sure sign of interference?
I am looking at purchasing a “BumbleBee” spectrum analyzer. Has anyone had experiance with these?
Thanks in advance
Reay
Chances are extremely high that it’s interference at the SM side - the AP can receive the SM, but the SM can’t receive the AP.
Put the SM in to spectrum analyzer mode (you need to do it from the customer site) and see what the SM is picking up. You will need someone reboot the AP at the same time so you can get an accurate reading.
The simplest solution is to put the SM on a reflector and lower the SM transmit power by 18dB. This sill increase the Rx sensitivity of the SM and isolate off-axis noise.
Alternately you may find you need to move the AP to another frequency.
Thank you Jerry,
Sure enough we found the interference source.
Our local Walmart superstore has just installed a 900Mhz RFID system.
According to the label on the unit itself, this system runs from 902-928 Mhz.
It is used for scanning inventory as it comes in the doors.
We found an antenae at each point of entry at the loading docks on this store.
Db’s are -39 on all freqs from 1/2 mile away.
Could not find anyone in the store who knew enough about it to change freqs or lower the power levels.
Any ideas??
-39dB? Yikes!
You will need to find out who installed the RFID system, and convince them that running it at 100% power is not necessary.
Even though you were there first, FCC will tell you to bug off. Eventually you will be able to get the FCC involved after many letters and no help from Wally - in the mean time you are suffering.
If it’s affecting one customer, an 18dB Yagi should offer enough off-axis isolation to take care of it (unless the WalMart is between the tower and the customer.) You’ll want to reduce the Tx power on the SM so you don’t blast the AP.
Jerry,
Thanks for the reply.
Of course the Walmart is between the tower and several customers.
The install was done by Walmart corp maintenance personell.
I have written an e-mail to corporate asking for cooperation on power levels or freq’s…It will be curious to see if that bears any fruit.
This will cause issues for a lot of us providers if this is a company wide project.
I could power up a 900 AP about 30 yards away, pointed to their back doors. Maybe that would get their attention
Now Now, be nice.
You catch more flies with honey than vinegar.
Of course when the little buggers don’t cooperate, that’s when the can of Raid comes out…
Yes I know,
It just sounds like so much fun.
Hey Jerry, thanks for all you do on this forum. I for one really do appreciate it. Your expertise has helped us on several occassions.
I will keep everyone posted on the Walmart cooperation or lack of.
Reay
Wait hold the phone…………………………….
A Walmart engineer just called, he said that he remotely turned the RFID system off, and would call me tomorrow to work out a permanent solution. He stated that he was familiar with Canopy and would work around us somehow.
He did and my customers are back up.
Wow, I’m impressed!!!
Well how about that?
very nice
The Walmart Engineer called back this morning.
Apparently, they have had quite a few interference issues with Canopy 900 gear in the last two weeks.
They use a 902-930 “circular” polarization @ 8 db gain.
The equipment manufacturer is TYCO. It is called RFID technology in case you’r interested.
According to TYCO’s website, Walmart is their #1 customer so watch out everybody.
At this poit in time they are not willing to change freq’s or lower power, however he stated that they are looking at narrowing their freq range.
He asked for the compass bearing and distance to affected SM’s. and aksed if we would be willing to just use one portion of the spectrum.
I agreed to attempt to keep every SM in the vicinity @ 906.
He did agree to leave their system down untill a solution is reached.
I expect to hear from him again next Tuesday. I will keep this thread updated with any news.
Reay
Ask him if there is a Tx power setting for his system. If it’s -39dB at 1/4 mile, it’s probably -30dB at the store which may be more than they need.
If he can use 924 and you use 906 for that sector, you will probably be alright.
Here is a link to the product. Not much info there.
http://catalog.tycoelectronics.com/TE/b … 3#features
At least he is being cooperative
Walmart Update
The Engineer called back this morning, they are going to leave the system off untill they can modify their config to use only the top 1/3rd of the 902-930 spectrum.
He also gave me a HOTLINE phone number that is always carried by one of their Engineers in case of any future interference issues.
He stated that the power levels are needed to penetrate the packaging of some inventory.
Can I get that Hotline phone number? I’ve got a mess of customers who just lost connectivity today!