Community discussions

MUM Europe 2020
 
mcrose
Frequent Visitor
Frequent Visitor
Topic Author
Posts: 60
Joined: Wed May 06, 2009 8:00 pm

802.11n wireless link signal strength issues

Tue Aug 17, 2010 4:47 pm

Recently upgraded a PtP link that had been using some older Tranzeo hardware with RB433s with R52Hn cards and RouterOS 4.11 installed on them. Antenna and cabling remained in place with switchover, and the link had been working great for many years so it's extremely doubtful there are any issues with the waveguide, antennas or alignment.

Edit: Should probably mention this is a 9.5 mile link with antennas ~120' in the air across flat terrain so the fresnel zone is quite clear. There's no geographical issue precluding communication between the two sites.

Mikrotik wireless configuration is basically default settings with exception of configured SSID and encryption, and set to use the channel the old hardware was transmitting on. Nstreme is enabled. When the radios were first installed, they linked up immediately. Same RSSI as old hardware, as expected (low -60s dBm) and no interference whatsoever (-105ish dBm noise floor). CCQ was great, 100%+ both directions and I was able to pass 36mbit over the link with the bandwidth test with no issues whatsoever for ~5 minutes. There was no variation in CCQ or actual throughput at this point.

Within a day, though, the link degraded. The client started dropping off for minutes at a time with logs stating that the loss was due to extensive data loss. The client was also seeing a rx rssi different than the tx rssi -- -85ish as opposed to the -62 it was transmitting at. CCQ also drops to ~40-60% in both directions at this point. After a while, the link would come back up, the rx rssi would go back up and traffic would pass properly again.

Testing at the client end shows that the issues are as expected due to downstream traffic. I can run an upload bandwidth from the test, which maxes out at ~5-6 mbit, abd after a few minutes the link will drop. A download bandwidth test kills the link immediately.
  • We've tried:
  • Looking for other people transmitting via the freq usage feature. Noise floor is extremely low (-105 dBm+ across all frequencies) and no transmissions on any frequencies are seen.
  • Different frequencies; no effect whatsoever.
  • Dropping the channel width down; raised RSSI slightly keeping it from dropping offline continually.
  • Limiting it to 802.11a-only modulations; seemed slightly better performance but still drops for a few minutes approx every hour.
  • Disabled Nstreme; connection performance got worse and the link could barely be sustained.
Testing with the previous hardware shows a stable link so it's not that the antenna or cabling were damaged during the switch. I suspect this is due to a bum radio and we're ordering a replacement at the moment. Just in case it's not, though, due to the wide variety of opinions on 802.11n and Mikrotik hardware (seeming to range from it's the best thing since sliced bread to that it's fundamentally broken and never works) I figured I'd ask if anyone else has seen these sort of symptoms. If so, what resolved them? Thanks in advance!
 
0ldman
Forum Guru
Forum Guru
Posts: 1446
Joined: Thu Jul 27, 2006 5:01 am

Re: 802.11n wireless link signal strength issues

Wed Aug 18, 2010 1:47 am

Sounds like issues I had with an R52HN board.

Worked great during initial testing. I burn in my APs for a bit before I put them out there, so I went to test it later on and signal went from the -50s to the -80s.

Reboot, no change, powered down for maybe 10 minutes, -50s. Once it had time to get hot, -80s again.

Swapped the card, never had another problem.
 
mcrose
Frequent Visitor
Frequent Visitor
Topic Author
Posts: 60
Joined: Wed May 06, 2009 8:00 pm

Re: 802.11n wireless link signal strength issues

Thu Aug 19, 2010 8:22 pm

As far as I can tell it's not a card issue. Purchased two additional cards, swapped the radios out individually on both ends of the link. Issues persisted no matter what card pairs were in the link. However, was able to stabilize the link by doing the following:

Setting the cards to 802.11a-only mode.
Limiting modulation to a maximum of 36mbit on both ends of the link
Ignoring radio card's eeprom transmit power config and setting the card to use 22dBm at all modulations.
Setting hardware retries value to 10.

Signal strength readings are still quite wonky. The client sees -84 dBm signal, transmits at -63dBm and a noise floor of -85 dBm. Despite the apparent 1 dB SNR radio the radio still works properly at 36mbit both directions -- get ~25 mbit TCP throughput unidirectional, ~11 mbit TCP throughput bidirectional. CCQ stays at ~100%. (See attached screenshot.) The AP sees a noise floor or -108 dBm and the same signal values but in the opposite direction.

I have double-checked, system is using the latest routerboard image and OS and should not be running out of date firmware for these cards. Has anyone seen signal level issues like this that were not caused by bad hardware? Thanks in advance.
You do not have the required permissions to view the files attached to this post.
 
dainen
newbie
Posts: 38
Joined: Tue Jul 05, 2005 12:33 pm
Location: Byron Bay, Australia
Contact:

Re: 802.11n wireless link signal strength issues

Fri Aug 20, 2010 4:41 am

Worked great during initial testing. I burn in my APs for a bit before I put them out there, so I went to test it later on and signal went from the -50s to the -80s.

Swapped the card, never had another problem.
We had the exact same problem.
We have a 33km link with 433AH (ROS 4.11) and R5H running at 5ghz with nstreme getting around -65 / -65 noise floor around -105. Its been in use for over 6 months with no issues.
Replaced the station end with a R52Hn signal was -68/-65 then a few minutes later the RX would jump to -88
We put the R5H back in and its all running perfectly again.

Not sure if its an incompatibility between the cards or something else...
 
danielillu
Member Candidate
Member Candidate
Posts: 110
Joined: Sun Aug 27, 2006 5:37 am
Location: Barcelona, Spain

Re: 802.11n wireless link signal strength issues

Fri Aug 20, 2010 2:39 pm

Same problem here. I have a very short link that can only be used at 802.11A with both chains active because when using 11N it announces very low CCQs and signal jump 20dBi.

I bought that link as soon as my distributor had R52HN in stock. Maybe there were many defective units then?

I think you gave me another way to test. I'm desesperating with this link.

Link info: about 5 km. Dual polarity (JRC-24 duplex), <1m coaxial. It should work flawslessly at about -65 if I remember well.

On the other side of the tower there's another link with same specs (hardware, distance, geography) sync'ed at 150mbps stable. It should push up to 300mbps but it doesn't, it get jumping all time.

During september I will change that radios. just to try it.
 
taduikis
Member
Member
Posts: 423
Joined: Sat Jul 07, 2007 12:09 pm

Re: 802.11n wireless link signal strength issues

Fri Aug 27, 2010 11:54 pm

This post finally approves my concerns about R52N (h or not, whatever) cards. I've been experiencing all mentioned odd behavior and could tell even more bad things about them. As a result, all my bought R52H cards are now lying in the drawer unused.. So I almost done my conclusions about this card. Which in one word would describe as "crap".

Currently, the best card I've had in my hands is R5H. No problems with them whatsoever. They all perform just brilliantly. If you don't need N of course.
 
MyThoughts
Member Candidate
Member Candidate
Posts: 210
Joined: Sat Sep 17, 2005 9:07 pm

Re: 802.11n wireless link signal strength issues

Sat Aug 28, 2010 5:09 am

See my post http://forum.mikrotik.com/viewtopic.php?f=1&t=44299

Is the link you upgraded using a single antenna and now a single chain on the r52Hn?

If you are using a single chain and using v4.1x then your problem may be the RouterOS software. From my testing when using a single chain on a 'N' based card that is configured as an AP with v4.1x there is a bug in RouterOS that prevents the card from functioning properly without at least a 2nd chain physically connected to an appropriate antenna (note only connected, RouterOS can still be set to use only a single chain).

If you only have a single chain connected to an antenna, try updating to v5.0b6 as this solved the problem in my testing. You may have still see signal issues (again see my link above) but the link should actually work.

I have emailed Mikrotik support with the issue, but have been out of town and have been unable to re-setup my test and give them the necessary Supout files. If anyone else verifies my results please get a supout file for the before and after sent to Mikrotik.

Cheers

Note: my tests were preformed on Ubiquiti SR71-5s, and Ubiquiti SR71-As
 
mcrose
Frequent Visitor
Frequent Visitor
Topic Author
Posts: 60
Joined: Wed May 06, 2009 8:00 pm

Re: 802.11n wireless link signal strength issues

Fri Sep 10, 2010 6:14 pm

It is. second chain has nothing connected to it whatsoever.

However, with the changes we've made (802.11a only, 36 mbit max modulation, no n modulations, force 22 dbm tx power for all modulations, 10 hw retries, etc etc) even with the odd rssi reporting issues it's at least staying up and mostly stable, and disconnections are only a few hundredths of a second at most. It's not a fast link, but it's good enough for my purposes.
 
alelogman
just joined
Posts: 1
Joined: Thu Nov 04, 2010 8:05 am

Re: 802.11n wireless link signal strength issues

Sat Nov 06, 2010 9:09 am

Sounds complicated to me but trying to figure out a prob here. Signal readings twists my brains.....
 
nordex
Frequent Visitor
Frequent Visitor
Posts: 91
Joined: Fri Mar 23, 2007 7:46 pm
Location: Croatia

Re: 802.11n wireless link signal strength issues

Mon Jan 24, 2011 8:30 pm

So, I see that others still have this 'signal jumping' issue.
I've tried with the latest RouterOS version but the problem is still active.

Is there any solution for R52hn card problem ?
 
User avatar
talo1019
Frequent Visitor
Frequent Visitor
Posts: 54
Joined: Sun Jan 24, 2010 6:48 am
Location: Taiwan
Contact:

Re: 802.11n wireless link signal strength issues

Wed Mar 23, 2011 6:32 am

May I ask the Rx issues that people are experiencing. Is this only for the 5ghz or 2.4ghz as well?

Who is online

Users browsing this forum: No registered users and 12 guests