I have a SM that is very close to an AP (mounted on a water tank). The SM has problems staying registered and through troubleshooting, I’ve determined that this is somehow related to the AP thinking the distance has changed. These are 900 MHz Advantage units.
Below are examples of readings from the AP and SM showing at one point the distance is 588 feet and then 441 feet. This constantly switches back and forth.
AP Reading 1:
LUID: 002 : MAC: 0a-00-3e-xx-xx-xx State: IN SESSION (Encrypt Active)
Site Name :
Software Version : CANOPY 7.3.6 Oct 24 2005 12:06:56
Software Boot Version : CANOPYBOOT 3.0
FPGA Version : 070605 (DES Sched) P9
Session Timeout: 0, AirDelay 4 (approximately 0.11 miles (588 feet))
Session Count: 11, Reg Count 12, Re-Reg Count 3
RSSI (Avg/Last): 1542/1544 Jitter (Avg/Last): 2/3 Power Level (Avg/Last): -62/-62
DnRate(APCAP): 20000 DnLimit(APCAP): 500000 UpRate(APCAP): 20000 UpLimit(APCAP): 500000 (kbit)
LoUpCIR(D): 0 LoDnCIR(D): 0 (kbps)
Rate : VC 18 Rate 1X/1X
SM Reading 1:
Session Status REGISTERED
Registered AP 0a-00-3e-xx-xx-xx
RSSI 1593 (-64 dBm)
Jitter 6
Air Delay 4 (approximately 0.11 miles (588 feet))
At this point, the unit disconnected and a few minutes later, registered again with a different range:
AP Reading 2:
LUID: 002 : MAC: 0a-00-3e-xx-xx-xx State: IN SESSION (Encrypt Active)
Site Name :
Software Version : CANOPY 7.3.6 Oct 24 2005 12:06:56
Software Boot Version : CANOPYBOOT 3.0
FPGA Version : 070605 (DES Sched) P9
Session Timeout: 0, AirDelay 3 (approximately 0.08 miles (441 feet))
Session Count: 13, Reg Count 14, Re-Reg Count 3
RSSI (Avg/Last): 1562/1552 Jitter (Avg/Last): 5/6 Power Level (Avg/Last): -61/-62
DnRate(APCAP): 20000 DnLimit(APCAP): 500000 UpRate(APCAP): 20000 UpLimit(APCAP): 500000 (kbit)
LoUpCIR(D): 0 LoDnCIR(D): 0 (kbps)
Rate : VC 18 Rate 1X/1X
SM Reading 2:
Session Status REGISTERED
Registered AP 0a-00-3e-xx-xx-xx
RSSI 1628 (-63 dBm)
Jitter 4
Air Delay 3 (approximately 0.08 miles (441 feet))
I’ve done quite a bit of researching on this forum and troubleshooting with lots of different settings, but I’m not completely through trying out different options.
I don’t think this is a desensitized AP because all the power levels on the AP are within a few dBm of each other.
But I’m curious if anyone else on this forum has seen a situation where the range switched back and forth without the unit physically moving. Anyone have any ideas on why the range would alternate?
If nothing else, what is the closest successful link you have?
Thanks,
John Robbins
Your Jitter (Avg/Last): 5/6 is high.
Looks like you don’t have LOS.
Change to hardware scheduling, this could help.
Do a site survey to see what you have around in the 900 MHz band, you will need 8 MHz of free not used spectrum.
I’m not sure why but I have a shot that’s a little over 9 miles and if you look at it one day it’ll say 9.17 miles, another it’ll say like 10.1 miles.
It does fluctuate quite a bit - but still works fine.
I am guessing that the AP or SM is getting a very strong early reflection from a nearby surface or the water tank itself.
What antenna are you using? I amd guessing Integrated. Try tilting the SM antenna way up, or down toward the ground. This might keep it from being able to see reflected signals.
What is the power level set on the SM? Try playing around with that a little.
Is there something else on the tower at or around the AP’s freq?
To answer everyone’s questions so far:
I am already running hardware scheduling. If you were wondering why a link so close was running 1X/1X, it’s because I set 2X mode to disabled for testing, since the link wasn’t stable.
Today the jitter has stayed around 2-3 and the link disconnected only a few times. Yesterday it was very bad, but we also had some very strong weather, so that may have aggravated the situation some (but only on this SM).
I’ve run site survey and the spectrum has some noise, but the SM is well above the floor on and around 924 MHz, so that’s what I’m set at.
I’ve tried adjusting the power on the SM and the AP, but it didn’t change the problem. Currently set at 22 dBm. The SM is connectorized with a MaxRad antenna.
I think Jerry is right about there being some reflection. I have found one other SM on another site we have (which happens to be a Water Tank as well). This SM is close (0.41 miles) to the AP as well and my logs show that the stated distance has changed at times. I have other SMs at sites that are half a mile to the AP and they don’t have problems, so it could be the specific layout of these two particular SMs and the water tanks where the APs are mounted. I will try repositioning the SM antenna and possibly the AP antenna to minimize the chances of reflection from the water tank.
If anyone has had experience with mounting APs on the sides of water tanks, I’m open to suggestions. We’re down on the hand rail, not on the top of the water tank. Any ways of mounting the AP and antenna so that reflection from the water tank itself is minimized?
Thanks for all your help on this,
John
John,
Is the SM on the water tank, Pointing against the water tank or towards the water tank?
ie… <<antenna(Water Tank) or >>Antenna(Water Tank) ?
Also, is this SM near a building?
SM is on a building pointed towards the water tank. The AP is on the hand rail of the water tank.
The building the SM is on isn’t metal roofed. It’s an older wood framed brick building with a shingled roof.
Try repositioning the SM antenna.
Was I correct in assuming Integrated 900AP? The antenna in there is a Cardiod pattern with a huge rear lobe. The big metal plane of the water tower behind the AP is reflecting the rear lobe beck into the main lobe. The distant SM’s can’t see it, but the closer SM can.
Ideally you would be on top of the water tower. Alternately an RF absorber behind the AP will reduce the rear lobe reflection which will improve performance overall. If that doesn’t work, then a connectorized AP with a Sectorized antenna in the answer as they have much smaller rear lobes and better forward sensitivity.
Hey!
Ummmm . . .
Why would you want the power level below the max (22dbm), expecially on the SM side?