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VistaVox
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Failing Cards

Fri Jul 27, 2007 11:42 pm

I've had a problem recently in 3 different APs. Two were using 8602+ cards to broadcast, and the other was using an xr2. The problem is that the cards will broadcast a SSID and it can be read by MikroTik devices, Laptops, etc., but no device can connect to the SSID. Once the card has been replaced the problem goes away.

It is quite obviously not a routerboard problem, just a card problem...any ideas? This is getting very frustrating as most of our APs are 100+ft off the ground, and it is very hard to replace those cards while strapped to a tower.
 
MyThoughts
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Re: Failing Cards

Sat Jul 28, 2007 3:29 pm

Your problem sounds like the TX side of the card is working correctly but the reciever is blown/damaged.
If you setup a small lab to test the cards, I believe you will find that they do in fact 'work', just not correctly.

If this is your problem... after setting up two test units (one with a good known working card, the other with a suspected damaged card). You will see that they will connect but on the unit with the damaged card the Rx will be ~15dB off the Tx signal strength.

What type of antennas are these cards powering? Have you had any really strong sustained winds lately? Have you had any thunderstorms around the suspect towers?

Cheers
 
cmacneill
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Re: Failing Cards

Sat Jul 28, 2007 6:34 pm

I bought 10 x EnGenius/Senao 8602 cards and had so many problems I ended up replacing them with Wistron CM9. I haven't got around to going through them methodically to determine which are good and which are bad.
 
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ghmorris
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Re: Failing Cards

Sat Jul 28, 2007 7:00 pm

You guys are doing well. We had to change out 60+ 8602s.

We are seeing some problems with R52s losing the diversity switch (20dB loss in sensitivity) in thunderstorms as well.

George
 
VistaVox
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Re: Failing Cards

Sat Jul 28, 2007 8:26 pm

What type of antennas are these cards powering? Have you had any really strong sustained winds lately? Have you had any thunderstorms around the suspect towers?
The xr2 was powering a 12dbi omni, 1 8602 was powering a 10dbi omni, 1 8602 was poewring a 12 dbi omni.

No strong winds to speak of, and only one of the 8602 cards was in the midst of thunderstorms(for about 1 whole week, strong ones too).

If I get a chance I will try out that little lab you described. Is there anything we can do to prevent/stop this, or atleast detect it before we upset customers?
 
bushy
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Re: Failing Cards

Sat Jul 28, 2007 11:51 pm

The xr2 was powering a 12dbi omni, 1 8602 was powering a 10dbi omni, 1 8602 was poewring a 12 dbi omni.
What brand of omnis are you using ? Some brands will kill mini-cards , there is a thread here somewhere about it.
 
MyThoughts
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Re: Failing Cards

Sun Jul 29, 2007 12:16 am

I've lost about 9 cards, all between 2 different sites.
5 CM9s
3 SR2s
1 NMP-8602

Interesting enough all these sites had 2 radios in the same RB532, one running a backhaul connection the other the omni. I have only lost cards that were powering the omni antenna and have never the card powering the other antenna (typcially a 2.4 GHz 24 dBi grid).

After some furthor comparison to other sites I narrowed the issue down two types of omni antenna I was using (one 12 sbi the other 15dbi). I suspect that the smooth PVC casing on the antennas (something akin to the 12 dBi Hyperlink outdoor omni), was building up a small static charge that would discharge into the radio. On one of the sites i had Atellicon gas discharge protectors in place, they did nothing to help. All i did was 'rough'n' up the antenna (sandpaper, course grit), that was a little over a year ago, and I haven't lost a radio since. I haven't the time to setup a proper experiment and prove my theory, but if anyone is up to doing it I'd be very interested in the results.

Cheers
 
cmacneill
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Re: Failing Cards

Sun Jul 29, 2007 1:59 am

The comment about smooth PVC surface on the Omni causing static build up seems to be counter intuitive. I would have thought a rough surface would cause more air resistance and hence higher static build up?

Most directional antennae have a metal backplate which would tend to act as a static drain. The trouble with an Omni is that it has to be metal free through 360 degrees.

I wonder is any of these Omnis that have caused problems have their coax cable shield grounded or not?
 
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tgrand
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Re: Failing Cards

Sun Jul 29, 2007 4:37 am

My Omnis have been modified to include 2 strands of solid copper wire lightly coiled to the top of the antenna and twisted together at the top and bottom, as well as grounded.
 
bushy
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Re: Failing Cards

Sun Jul 29, 2007 10:20 am

If you measure between the centre pin and outer of the connector of the omnis killing the cards with a meter you will probably find they are open-circuit, so there is no way to bleed away charge from the centre pin,lightning protectors won't be much use either.
You can either get different omnis or open the ones you have and add something to bleed off charge (go ask a ham radio guy how to do it I can't remember but its simple)

<edit>
have one of these type connected to cm9 card in an exposed spot for a few years with no problems .
http://www.wi-pipe.com/2360-10dbi-omni-p-48.html
 
jo2jo
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Re: Failing Cards

Sun Jul 29, 2007 11:25 am

There is a long thread on here about this exact issues with Omni's but NOT with directonal.

I think a solution of the thread was to put small copper wire in places to dissapate any charge build up.

btw, why do you have so many 2.4ghz Omni's next to each other like that (you described 3 400mw cards, coming from a RB each to Omnis)
 
MyThoughts
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Re: Failing Cards

Mon Jul 30, 2007 3:46 pm

Inreply to cmacneill's comment on the rough vs. smooth surface, I would absolutely agree with him. Smooth surfaces tend to have laminar flow over the surface, this will still create a static buildup but it will not be concentrated at any particular point. A rough surface on the other hand will have a turbulent flow (more resistence), and yes this should create more of a potential then the smooth situation. The rough surface will also have areas where the charge accumulates doesn't flow evenly over the object.

Why did I rough'n up the omni, simple... I was at a loss and just tried what I did becuase I really didn't have an easier solution, static electricity can be a strange and unpredictable beast, and I am no expert, but this seemed to work for me.
In retrospect, I may have just gotten lucky. I do remember when this happened to me there was a post regarding it and it had a solution that sounds similar to tgrand's.

this is the other topic that had a possible solution, about half way down 1st page see Gerard's post.
http://forum.mikrotik.com/viewtopic.php ... 734&hilit=

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