Radio Card Life Span

I had a problem with one of my MeshAP's radio card. It pop out of it's PCI slot such that a PCMCIA adapter with a 200 mW radio card. I notice that the signal was starting to fade. After a months of loosing power the radio card lost many dbi's. Switching the radio cards I saw that the newer card was yet again stronger. As I brought it back to the lab and tested the radio card, it once again started to work.

Scratching my head, yet again I asked a few people about it. A number of other observers indicated that Radio cards loose power over time and then simple stop working. This concerns me as radio cards in my opinion should last a long time not a few years.

The new question is how many times will I have to change radio cards? What is the life cycle of these units? When should I expect failure to occur. Testing the wireless mesh can answer these questions.

Can the answer to these question be with a simple maintenance approach? I remember seeing a maintenance department change all the light bulbs in every floor of a building. So when I talk to the manager of the maintenance people he said that getting calls about burnt out lights was his number one problem and that two individuals full time job was to change light bulbs. I ask him how this was saving money? He said that in two weeks he changes all the light bulbs and frees up two people time for a year. Is this the answer to changing out radio cards?

Should we expect a life expectancy of 1 year and then change them out? I will review the economics but I think I will have to add this to the financial model.