we have a 4-port miniPCI / PCI Adapter with four CM9 cards.
Three of them running on 5GHz with sector-antennas. One is connected to a 2,4Ghz Omni.
The one connected to the omni had a amplifier failure after 15 hours. We replaced it and the new card’s amplifier failed also after about 15 hours.
Now we’re searching for an reason for that failure. We don’t want to try another card because we think that it’ll failure also.
Before the failure, the cards worked fine… a “scan” showed up to 70 wlan’s .. after the failure we now see only 25 wlan’s and the best of them has a signal of -80db.
I really doubt this is an “amplifier” failure. My money is on the diversity switch getting damaged - most likely due to ESD. I’ve had that happen to quite a few CM9’s for various reasons - all more than likely due to improper or missing Earth grounding.
You may want to see if your omni antenna is designed such that the center conductor is at the same potential as the shell - most manufacturers refer to this as the antenna being “DC grounded” or something similar. The easiest way to tell if it is or not in the field is to use a multimeter or continuity probe and check for resistance or continuity from the center pin to shell of the antenna’s RF connector. If it reads as a short, then it’s the “DC grounded” variety - which is what you want.
If you don’t have that kind of antenna design, you can put in a “shorted stub” style 1/4 wave lightning arrestor instead. RF Linx carries them - http://www.rflinx.com/products/lightning-arrestors/ , but other vendors do as well if you look around.
The theory behind these failures is static buildup due to wind blowing over the antenna, or from nearby lightning, will eventually cause a static arc-over and pop the diversity switch. In my experience, this usually manifested itself as the radio going “deaf” - it transmitted nearly as well as before, but couldn’t hear (receive). This sounds much like what you’ve reported as well.
Well, that’s my experience, for what it’s worth. Let us know how it turns out.
we talked about this issue today and i also thought that there is some grounding problem so esd-issues arise. so i absolutely agree to what bradg says and i think it’s the only possible thing.
Another possibility is a bad SWR (Standing Wave Ratio) being presented to the output of the card.
Meaning that there may be a problem somewhere from the RF connector of the card up to and possibly including the antenna itself… eg: bad pigtail, connector, coax or antenna.
True, this is possible as well. But, the symptoms of 1) working well initially, then 2) not working well after a period of time, and finally 3) not being able to “hear” makes me believe it’s the diversity switch issue.
And, since the CM9’s are known to exhibit this problem when the switch gets a healthy dose of ESD, that seems to be the most likely culprit to me.
My colleague checked the antenna now and it is NOT dc grounded!
We will now try to use a Compex wlan card instead of the cm9 because we have a AP at another location which has exactly the same omni antenna (but with a Compex card) and it’s working since 1/2 year without any problems.
I’ve had the same problem on a similar card that has the same diversity antenna switch IC. It only happened on my outdoor APs and it was usually after foul weather. I was able to repair the cards by replacing the diversity antenna switch IC. Since then I have installed PolyPhaser high pass filter / multi-strike lightning arrestors and have had no problems for over a year now.
