[Mikrotik] 802.11n vs 802.11a

Chuck Hogg chuck at shelbybb.com
Tue Apr 24 13:49:26 CDT 2012


To be honest, I'd bet you are in a sidelobe or very close and every so
often it drops into the sidelobe.

My techs don't believe me when I tell them that H/V signals should be very
similar within 2-3 dB of each other or they will not work properly.  Case
in point, techs installed a link that was -71/-58.  The antenna needed
final adjustment on the elevation.  Brought the signal to -60/-58 and the
link is now stable.  I have seen this issue with both UBNT and MikroTik
products.

Regards,
Chuck


On Tue, Apr 24, 2012 at 12:26 PM, Matt Larsen - Lists
<lists at manageisp.com>wrote:

> On 4/24/2012 10:02 AM, Mike Hammett wrote:
>
>> Bad card, pigtail, jumper, feedhorn?
>>
>>
> Trust me, we exhausted just about every possibility of hardware failure.
> All it did was cost me a lot of money before we figured the 802.11a
> solution out.   I can't even claim credit for that - Travis Johnson was the
> one who suggested it because he has been having the same issues with
> 802.11n.
>
> Matt Larsen
> vistabeam.com
>
>
>
>
>> -----
>> Mike Hammett
>> Intelligent Computing Solutions
>> http://www.ics-il.com
>>
>> ----- Original Message -----
>> From: "Matt Larsen - Lists"<lists at manageisp.com>
>> To: "Mikrotik discussions"<mikrotik at mail.**butchevans.com<mikrotik at mail.butchevans.com>
>> >
>> Sent: Tuesday, April 24, 2012 11:01:07 AM
>> Subject: Re: [Mikrotik] 802.11n vs 802.11a
>>
>> All of the 802.11n paths that had problems tended to have one chain out
>> of four (tx/rx on both polarities) that was much worse than the
>> others.   This lead to the big variances in CCQ, is what I have been
>> told.    I don't have a good technical explanation for it other than
>> 802.11a modulation ended up making the links much more solid and got our
>> CCQs back up to 90%+.
>>
>> We do still have one 65+ mile shot using the 802.11n modulations and it
>> appears to be working fine, but that link is on 4' Radiowaves dishes,
>> plenty of clearance along the path and has -65 signals on all of the
>> chains.    It is also a backup link at this point and not running a lot
>> of traffic so it doesn't see the same kind of load that my other links
>> are getting.   Before we figured this problem out, we were seeing great
>> results on testing on the long 802.11n links but they would start
>> getting real flaky when we put heavy loads on them.
>>
>> Matt Larsen
>> vistabeam.com
>>
>>
>> On 4/24/2012 9:43 AM, Mike Hammett wrote:
>>
>>> Wouldn't multipath be *better* for N?
>>>
>>>
>>>
>>> -----
>>> Mike Hammett
>>> Intelligent Computing Solutions
>>> http://www.ics-il.com
>>>
>>> ----- Original Message -----
>>> From: "Matt Larsen - Lists"<lists at manageisp.com>
>>> To: "Mikrotik discussions"<mikrotik at mail.**butchevans.com<mikrotik at mail.butchevans.com>
>>> >
>>> Sent: Tuesday, April 24, 2012 10:25:15 AM
>>> Subject: [Mikrotik] 802.11n vs 802.11a
>>>
>>> We are finding out that 802.11n links do some weird things when they get
>>> over 25 miles.They will run 70meg and then drop to 5 even though the
>>> signals and other RF conditions have not changed.As you can imagine,
>>> this makes latency go all over the place.We found that by setting them
>>> to 802.11a mode, we can get them to carry 30meg consistently with a much
>>> narrower range of latency results.    This is reflected in much higher
>>> CCQ% on the 802.11a links vs the 802.11n links.   Also seems like
>>> Nstreme (not NV2) with a framer policy of 'none' and CSMA disabled is
>>> the most stable setup.
>>>
>>>
>>> Just thought some folks might find this useful.   Butch has said that
>>> some of our 802.11n problems may have had to do with multipath.    YMMV.
>>>
>>>
>>> Matt Larsen
>>> vistabeam.com
>>>
>>>
>>>
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